server: add IR support for DB-to-DB joins

GJ IR changes cherry-picked from the original GJ branch. There is a separate (can be merged independently) PR for metadata changes (#1727) and there will be a different PR upcoming PR for execution changes.

https://github.com/hasura/graphql-engine-mono/pull/1810

Co-authored-by: Vamshi Surabhi <6562944+0x777@users.noreply.github.com>
GitOrigin-RevId: c31956af29dc9c9b75d002aba7d93c230697c5f4

server/src-lib/Hasura/Backends/BigQuery/FromIr.hs

@@ -791,17 +791,6 @@ fromAnnFieldsG existingJoins stringifyNumbers (Rql.FieldName name, field) =
         (\aliasedThing ->
            JoinFieldSource (Aliased {aliasedThing, aliasedAlias = name}))
         (fromArraySelectG arraySelectG)
-    -- this will be gone once the code which collects remote joins from the IR
-    -- emits a modified IR where remote relationships can't be reached
-    Ir.AFRemote _ ->
-      pure
-        (ExpressionFieldSource
-           Aliased
-             { aliasedThing = BigQuery.ValueExpression (StringValue "null: remote field selected")
-             , aliasedAlias = name
-             })
-    -- TODO: implement this
-    Ir.AFDBRemote _ -> error "FIXME"
 
 
 -- | Here is where we project a field as a column expression. If

server/src-lib/Hasura/Backends/BigQuery/Instances/Schema.hs

@@ -77,7 +77,7 @@ bqBuildTableRelayQueryFields
   -> G.Name
   -> NESeq (ColumnInfo 'BigQuery)
   -> SelPermInfo  'BigQuery
-  -> m [FieldParser n (QueryRootField UnpreparedValue UnpreparedValue)]
+  -> m [FieldParser n (QueryRootField UnpreparedValue)]
 bqBuildTableRelayQueryFields _sourceName _sourceInfo _tableName _tableInfo _gqlName _pkeyColumns _selPerms =
   pure []
 
@@ -91,7 +91,7 @@ bqBuildTableInsertMutationFields
   -> InsPermInfo 'BigQuery
   -> Maybe (SelPermInfo 'BigQuery)
   -> Maybe (UpdPermInfo 'BigQuery)
-  -> m [FieldParser n (MutationRootField UnpreparedValue UnpreparedValue)]
+  -> m [FieldParser n (MutationRootField UnpreparedValue)]
 bqBuildTableInsertMutationFields _sourceName _sourceInfo _tableName _tableInfo _gqlName _insPerms _selPerms _updPerms =
   pure []
 
@@ -104,7 +104,7 @@ bqBuildTableUpdateMutationFields
   -> G.Name
   -> UpdPermInfo 'BigQuery
   -> Maybe (SelPermInfo 'BigQuery)
-  -> m [FieldParser n (MutationRootField UnpreparedValue UnpreparedValue)]
+  -> m [FieldParser n (MutationRootField UnpreparedValue)]
 bqBuildTableUpdateMutationFields _sourceName _sourceInfo _tableName _tableInfo _gqlName _updPerns _selPerms =
   pure []
 
@@ -117,7 +117,7 @@ bqBuildTableDeleteMutationFields
   -> G.Name
   -> DelPermInfo 'BigQuery
   -> Maybe (SelPermInfo 'BigQuery)
-  -> m [FieldParser n (MutationRootField UnpreparedValue UnpreparedValue)]
+  -> m [FieldParser n (MutationRootField UnpreparedValue)]
 bqBuildTableDeleteMutationFields _sourceName _sourceInfo _tableName _tableInfo _gqlName _delPerns _selPerms =
   pure []
 
@@ -129,7 +129,7 @@ bqBuildFunctionQueryFields
     -> FunctionInfo 'BigQuery
     -> TableName 'BigQuery
     -> SelPermInfo 'BigQuery
-    -> m [FieldParser n (QueryRootField UnpreparedValue UnpreparedValue)]
+    -> m [FieldParser n (QueryRootField UnpreparedValue)]
 bqBuildFunctionQueryFields _ _ _ _ _ _ =
   pure []
 
@@ -142,7 +142,7 @@ bqBuildFunctionRelayQueryFields
   -> TableName    'BigQuery
   -> NESeq (ColumnInfo 'BigQuery)
   -> SelPermInfo  'BigQuery
-  -> m [FieldParser n (QueryRootField UnpreparedValue UnpreparedValue)]
+  -> m [FieldParser n (QueryRootField UnpreparedValue)]
 bqBuildFunctionRelayQueryFields _sourceName _sourceInfo _functionName _functionInfo _tableName _pkeyColumns _selPerms =
   pure []
 
@@ -154,7 +154,7 @@ bqBuildFunctionMutationFields
     -> FunctionInfo 'BigQuery
     -> TableName 'BigQuery
     -> SelPermInfo 'BigQuery
-    -> m [FieldParser n (MutationRootField UnpreparedValue UnpreparedValue)]
+    -> m [FieldParser n (MutationRootField UnpreparedValue)]
 bqBuildFunctionMutationFields _ _ _ _ _ _ =
   pure []
 

server/src-lib/Hasura/Backends/MSSQL/FromIr.hs

@@ -727,18 +727,6 @@ fromAnnFieldsG existingJoins stringifyNumbers (IR.FieldName name, field) =
         (\aliasedThing ->
            JoinFieldSource (Aliased {aliasedThing, aliasedAlias = name}))
         (fromArraySelectG arraySelectG)
-    -- this will be gone once the code which collects remote joins from the IR
-    -- emits a modified IR where remote relationships can't be reached
-    IR.AFRemote _ ->
-      pure
-        (ExpressionFieldSource
-           Aliased
-             { aliasedThing = TSQL.ValueExpression
-                              (ODBC.TextValue "null: remote field selected")
-             , aliasedAlias = name
-             })
-    -- TODO: implement this
-    IR.AFDBRemote _ -> error "FIXME"
 
 -- | Here is where we project a field as a column expression. If
 -- number stringification is on, then we wrap it in a

server/src-lib/Hasura/Backends/MSSQL/Instances/Schema.hs

@@ -79,7 +79,7 @@ msBuildTableRelayQueryFields
   -> G.Name
   -> NESeq (ColumnInfo 'MSSQL)
   -> SelPermInfo  'MSSQL
-  -> m [FieldParser n (QueryRootField UnpreparedValue UnpreparedValue)]
+  -> m [FieldParser n (QueryRootField UnpreparedValue)]
 msBuildTableRelayQueryFields _sourceName _sourceInfo _tableName _tableInfo _gqlName _pkeyColumns _selPerms =
   pure []
 
@@ -93,7 +93,7 @@ msBuildTableInsertMutationFields
   -> InsPermInfo 'MSSQL
   -> Maybe (SelPermInfo 'MSSQL)
   -> Maybe (UpdPermInfo 'MSSQL)
-  -> m [FieldParser n (MutationRootField UnpreparedValue UnpreparedValue)]
+  -> m [FieldParser n (MutationRootField UnpreparedValue)]
 msBuildTableInsertMutationFields _sourceName _sourceInfo _tableName _tableInfo _gqlName _insPerms _selPerms _updPerms =
   pure []
 
@@ -106,7 +106,7 @@ msBuildTableUpdateMutationFields
   -> G.Name
   -> UpdPermInfo 'MSSQL
   -> Maybe (SelPermInfo 'MSSQL)
-  -> m [FieldParser n (MutationRootField UnpreparedValue UnpreparedValue)]
+  -> m [FieldParser n (MutationRootField UnpreparedValue)]
 msBuildTableUpdateMutationFields _sourceName _sourceInfo _tableName _tableInfo _gqlName _updPerns _selPerms =
   pure []
 
@@ -119,7 +119,7 @@ msBuildTableDeleteMutationFields
   -> G.Name
   -> DelPermInfo 'MSSQL
   -> Maybe (SelPermInfo 'MSSQL)
-  -> m [FieldParser n (MutationRootField UnpreparedValue UnpreparedValue)]
+  -> m [FieldParser n (MutationRootField UnpreparedValue)]
 msBuildTableDeleteMutationFields _sourceName _sourceInfo _tableName _tableInfo _gqlName _delPerns _selPerms =
   pure []
 
@@ -131,7 +131,7 @@ msBuildFunctionQueryFields
     -> FunctionInfo 'MSSQL
     -> TableName 'MSSQL
     -> SelPermInfo 'MSSQL
-    -> m [FieldParser n (QueryRootField UnpreparedValue UnpreparedValue)]
+    -> m [FieldParser n (QueryRootField UnpreparedValue)]
 msBuildFunctionQueryFields _ _ _ _ _ _ =
   pure []
 
@@ -144,7 +144,7 @@ msBuildFunctionRelayQueryFields
   -> TableName    'MSSQL
   -> NESeq (ColumnInfo 'MSSQL)
   -> SelPermInfo  'MSSQL
-  -> m [FieldParser n (QueryRootField UnpreparedValue UnpreparedValue)]
+  -> m [FieldParser n (QueryRootField UnpreparedValue)]
 msBuildFunctionRelayQueryFields _sourceName _sourceInfo _functionName _functionInfo _tableName _pkeyColumns _selPerms =
   pure []
 
@@ -156,7 +156,7 @@ msBuildFunctionMutationFields
     -> FunctionInfo 'MSSQL
     -> TableName 'MSSQL
     -> SelPermInfo 'MSSQL
-    -> m [FieldParser n (MutationRootField UnpreparedValue UnpreparedValue)]
+    -> m [FieldParser n (MutationRootField UnpreparedValue)]
 msBuildFunctionMutationFields _ _ _ _ _ _ =
   pure []
 

server/src-lib/Hasura/Backends/MySQL/Instances/Schema.hs

@@ -79,7 +79,7 @@ buildTableRelayQueryFields' ::
   G.Name ->
   NESeq (ColumnInfo 'MySQL) ->
   SelPermInfo 'MySQL ->
-  m [FieldParser n (QueryRootField UnpreparedValue UnpreparedValue)]
+  m [FieldParser n (QueryRootField UnpreparedValue)]
 buildTableRelayQueryFields' _sourceName _sourceInfo _tableName _tableInfo _gqlName _pkeyColumns _selPerms =
   pure []
 
@@ -94,7 +94,7 @@ buildTableInsertMutationFields' ::
   InsPermInfo 'MySQL ->
   Maybe (SelPermInfo 'MySQL) ->
   Maybe (UpdPermInfo 'MySQL) ->
-  m [FieldParser n (MutationRootField UnpreparedValue UnpreparedValue)]
+  m [FieldParser n (MutationRootField UnpreparedValue)]
 buildTableInsertMutationFields' _sourceName _sourceInfo _tableName _tableInfo _gqlName _insPerms _selPerms _updPerms =
   pure []
 
@@ -108,7 +108,7 @@ buildTableUpdateMutationFields' ::
   G.Name ->
   UpdPermInfo 'MySQL ->
   Maybe (SelPermInfo 'MySQL) ->
-  m [FieldParser n (MutationRootField UnpreparedValue UnpreparedValue)]
+  m [FieldParser n (MutationRootField UnpreparedValue)]
 buildTableUpdateMutationFields' _sourceName _sourceInfo _tableName _tableInfo _gqlName _updPerns _selPerms =
   pure []
 
@@ -122,7 +122,7 @@ buildTableDeleteMutationFields' ::
   G.Name ->
   DelPermInfo 'MySQL ->
   Maybe (SelPermInfo 'MySQL) ->
-  m [FieldParser n (MutationRootField UnpreparedValue UnpreparedValue)]
+  m [FieldParser n (MutationRootField UnpreparedValue)]
 buildTableDeleteMutationFields' _sourceName _sourceInfo _tableName _tableInfo _gqlName _delPerns _selPerms =
   pure []
 
@@ -135,7 +135,7 @@ buildFunctionQueryFields' ::
   FunctionInfo 'MySQL ->
   RQL.TableName 'MySQL ->
   SelPermInfo 'MySQL ->
-  m [FieldParser n (QueryRootField UnpreparedValue UnpreparedValue)]
+  m [FieldParser n (QueryRootField UnpreparedValue)]
 buildFunctionQueryFields' _ _ _ _ _ _ =
   pure []
 
@@ -149,7 +149,7 @@ buildFunctionRelayQueryFields' ::
   RQL.TableName 'MySQL ->
   NESeq (ColumnInfo 'MySQL) ->
   SelPermInfo 'MySQL ->
-  m [(FieldParser n (QueryRootField UnpreparedValue UnpreparedValue))]
+  m [FieldParser n (QueryRootField UnpreparedValue)]
 buildFunctionRelayQueryFields' _sourceName _sourceInfo _functionName _functionInfo _tableName _pkeyColumns _selPerms =
   pure []
 
@@ -162,7 +162,7 @@ buildFunctionMutationFields' ::
   FunctionInfo 'MySQL ->
   RQL.TableName 'MySQL ->
   SelPermInfo 'MySQL ->
-  m [FieldParser n (MutationRootField UnpreparedValue UnpreparedValue)]
+  m [FieldParser n (MutationRootField UnpreparedValue)]
 buildFunctionMutationFields' _ _ _ _ _ _ =
   pure []
 

server/src-lib/Hasura/Backends/Postgres/Instances/Schema.hs

@@ -67,7 +67,7 @@ class PostgresSchema (pgKind :: PostgresKind) where
     -> G.Name
     -> NESeq (ColumnInfo ('Postgres pgKind))
     -> SelPermInfo ('Postgres pgKind)
-    -> m [FieldParser n (QueryRootField UnpreparedValue UnpreparedValue)]
+    -> m [FieldParser n (QueryRootField UnpreparedValue)]
   pgkBuildFunctionRelayQueryFields
     :: BS.MonadBuildSchema ('Postgres pgKind) r m n
     => SourceName
@@ -77,7 +77,7 @@ class PostgresSchema (pgKind :: PostgresKind) where
     -> TableName ('Postgres pgKind)
     -> NESeq (ColumnInfo ('Postgres pgKind))
     -> SelPermInfo ('Postgres pgKind)
-    -> m [FieldParser n (QueryRootField UnpreparedValue UnpreparedValue)]
+    -> m [FieldParser n (QueryRootField UnpreparedValue)]
   pgkRelayExtension
     :: Maybe (XRelay ('Postgres pgKind))
   pgkNode
@@ -161,7 +161,7 @@ buildTableRelayQueryFields
   -> G.Name
   -> NESeq (ColumnInfo ('Postgres pgKind))
   -> SelPermInfo  ('Postgres pgKind)
-  -> m [FieldParser n (QueryRootField UnpreparedValue UnpreparedValue)]
+  -> m [FieldParser n (QueryRootField UnpreparedValue)]
 buildTableRelayQueryFields sourceName sourceInfo tableName tableInfo gqlName pkeyColumns selPerms = do
   let
     mkRF = RFDB sourceName
@@ -184,7 +184,7 @@ buildFunctionRelayQueryFields
   -> TableName    ('Postgres pgKind)
   -> NESeq (ColumnInfo ('Postgres pgKind))
   -> SelPermInfo  ('Postgres pgKind)
-  -> m [FieldParser n (QueryRootField UnpreparedValue UnpreparedValue)]
+  -> m [FieldParser n (QueryRootField UnpreparedValue)]
 buildFunctionRelayQueryFields sourceName sourceInfo functionName functionInfo tableName pkeyColumns selPerms = do
   funcName <- functionGraphQLName @('Postgres pgKind) functionName `onLeft` throwError
   let

server/src-lib/Hasura/Backends/Postgres/Translate/Select.hs

@@ -876,10 +876,6 @@ processAnnFields sourcePrefix fieldAlias similarArrFields annFields = do
 
       AFColumn c -> toSQLCol c
 
-      -- this will be gone once the code which collects remote joins from the IR
-      -- emits a modified IR where remote relationships can't be reached
-      AFRemote _ -> pure $ S.SELit "null: remote field selected"
-
       AFObjectRelation objSel -> withWriteObjectRelation $ do
         let AnnRelationSelectG relName relMapping annObjSel = objSel
             AnnObjectSelectG objAnnFields tableFrom tableFilter = annObjSel
@@ -928,9 +924,6 @@ processAnnFields sourcePrefix fieldAlias similarArrFields annFields = do
              , S.mkQIdenExp computedFieldSourcePrefix fieldName
              )
 
-      -- TODO: implement this
-      AFDBRemote _ -> error "FIXME"
-
 
   pure $ annRowToJson @pgKind fieldAlias fieldExps
 

server/src-lib/Hasura/GraphQL/Context.hs

@@ -30,8 +30,8 @@ data RoleContext a
 $(deriveToJSON hasuraJSON ''RoleContext)
 
 data GQLContext = GQLContext
-  { gqlQueryParser    ::        ParserFn (InsOrdHashMap G.Name (IR.QueryRootField    UnpreparedValue UnpreparedValue))
+  { gqlQueryParser    ::        ParserFn (InsOrdHashMap G.Name (IR.QueryRootField    UnpreparedValue))
-  , gqlMutationParser :: Maybe (ParserFn (InsOrdHashMap G.Name (IR.MutationRootField UnpreparedValue UnpreparedValue)))
+  , gqlMutationParser :: Maybe (ParserFn (InsOrdHashMap G.Name (IR.MutationRootField UnpreparedValue)))
   }
 
 instance J.ToJSON GQLContext where

server/src-lib/Hasura/GraphQL/Execute.hs

@@ -131,7 +131,7 @@ getExecPlanPartial userInfo sc queryType req =
 
 -- The graphql query is resolved into a sequence of execution operations
 data ResolvedExecutionPlan
-  = QueryExecutionPlan EB.ExecutionPlan [IR.QueryRootField UnpreparedValue UnpreparedValue] DirectiveMap
+  = QueryExecutionPlan EB.ExecutionPlan [IR.QueryRootField UnpreparedValue] DirectiveMap
   -- ^ query execution; remote schemas and introspection possible
   | MutationExecutionPlan EB.ExecutionPlan
   -- ^ mutation execution; only __typename introspection supported
@@ -157,7 +157,7 @@ data SubscriptionExecution
 buildSubscriptionPlan
   :: (MonadError QErr m)
   => UserInfo
-  -> InsOrdHashMap G.Name (IR.QueryRootField UnpreparedValue UnpreparedValue)
+  -> InsOrdHashMap G.Name (IR.QueryRootField UnpreparedValue)
   -> m SubscriptionExecution
 buildSubscriptionPlan userInfo rootFields = do
   (onSourceFields, noRelationActionFields) <- foldlM go (mempty, mempty) (OMap.toList rootFields)

server/src-lib/Hasura/GraphQL/Execute/Mutation.hs

@@ -84,7 +84,7 @@ convertMutationSelectionSet env logger gqlContext SQLGenCtx{stringifyNum} userIn
   (resolvedDirectives, resolvedSelSet) <- resolveVariables varDefs (fromMaybe Map.empty varValsM) directives fields
   -- Parse the GraphQL query into the RQL AST
   (unpreparedQueries, _reusability)
-    :: (OMap.InsOrdHashMap G.Name (MutationRootField UnpreparedValue UnpreparedValue), QueryReusability)
+    :: (OMap.InsOrdHashMap G.Name (MutationRootField UnpreparedValue), QueryReusability)
     <-(mutationParser >>> (`onLeft` reportParseErrors)) resolvedSelSet
 
   -- Process directives on the mutation
@@ -95,7 +95,7 @@ convertMutationSelectionSet env logger gqlContext SQLGenCtx{stringifyNum} userIn
   txs <- for unpreparedQueries \case
     RFDB sourceName exists ->
       AB.dispatchAnyBackend @BackendExecute exists
-        \(SourceConfigWith sourceConfig (MDBR db :: MutationDBRoot UnpreparedValue UnpreparedValue b)) -> do
+        \(SourceConfigWith (sourceConfig :: SourceConfig b) (MDBR db)) -> do
           let (noRelsDBAST, remoteJoins) = RJ.getRemoteJoinsMutationDB db
           dbStepInfo <- mkDBMutationPlan @b userInfo stringifyNum sourceName sourceConfig noRelsDBAST
           pure $ ExecStepDB [] (AB.mkAnyBackend dbStepInfo) remoteJoins

server/src-lib/Hasura/GraphQL/Execute/Query.hs

@@ -41,7 +41,7 @@ parseGraphQLQuery
   -> Maybe (HashMap G.Name J.Value)
   -> [G.Directive G.Name]
   -> G.SelectionSet G.NoFragments G.Name
-  -> m ( InsOrdHashMap G.Name (QueryRootField UnpreparedValue UnpreparedValue)
+  -> m ( InsOrdHashMap G.Name (QueryRootField UnpreparedValue)
        , QueryReusability
        , [G.Directive Variable]
        , G.SelectionSet G.NoFragments Variable
@@ -69,7 +69,7 @@ convertQuerySelSet
   -> [G.VariableDefinition]
   -> Maybe GH.VariableValues
   -> SetGraphqlIntrospectionOptions
-  -> m (ExecutionPlan, [QueryRootField UnpreparedValue UnpreparedValue], G.SelectionSet G.NoFragments Variable, DirectiveMap)
+  -> m (ExecutionPlan, [QueryRootField UnpreparedValue], G.SelectionSet G.NoFragments Variable, DirectiveMap)
 convertQuerySelSet env logger gqlContext userInfo manager reqHeaders directives fields varDefs varValsM
   introspectionDisabledRoles = do
   -- Parse the GraphQL query into the RQL AST
@@ -86,7 +86,7 @@ convertQuerySelSet env logger gqlContext userInfo manager reqHeaders directives
   executionPlan <- for unpreparedQueries \case
     RFDB sourceName exists ->
       AB.dispatchAnyBackend @BackendExecute exists
-        \(SourceConfigWith sourceConfig (QDBR db :: QueryDBRoot UnpreparedValue UnpreparedValue b)) -> do
+        \(SourceConfigWith (sourceConfig :: (SourceConfig b)) (QDBR db)) -> do
           let (noRelsDBAST, remoteJoins) = RJ.getRemoteJoins db
           dbStepInfo <- mkDBQueryPlan @b userInfo sourceName sourceConfig noRelsDBAST
           pure $ ExecStepDB [] (AB.mkAnyBackend dbStepInfo) remoteJoins

server/src-lib/Hasura/GraphQL/Execute/RemoteJoin/Collect.hs

@@ -52,8 +52,8 @@ import           Hasura.RQL.Types
 
 -- | Collects remote joins from the AST and also adds the necessary join fields
 getRemoteJoins
-  :: (Backend b)
+  :: Backend b
-  => QueryDB b r (UnpreparedValue b)
+  => QueryDB b (RemoteSelect UnpreparedValue) (UnpreparedValue b)
   -> (QueryDB b (Const Void) (UnpreparedValue b), Maybe RemoteJoins)
 getRemoteJoins = \case
   QDBMultipleRows s -> first QDBMultipleRows $ getRemoteJoinsSelect s
@@ -63,32 +63,32 @@ getRemoteJoins = \case
 
 -- | Traverse through 'AnnSimpleSel' and collect remote join fields (if any).
 getRemoteJoinsSelect
-  :: (Backend b)
+  :: Backend b
-  => AnnSimpleSelectG b r (UnpreparedValue b)
+  => AnnSimpleSelectG b (RemoteSelect UnpreparedValue) (UnpreparedValue b)
   -> (AnnSimpleSelectG b (Const Void) (UnpreparedValue b), Maybe RemoteJoins)
 getRemoteJoinsSelect =
   second mapToNonEmpty . flip runState mempty . transformSelect mempty
 
 -- | Traverse through @'AnnAggregateSelect' and collect remote join fields (if any).
 getRemoteJoinsAggregateSelect
-  :: (Backend b)
+  :: Backend b
-  => AnnAggregateSelectG b r (UnpreparedValue b)
+  => AnnAggregateSelectG b (RemoteSelect UnpreparedValue) (UnpreparedValue b)
   -> (AnnAggregateSelectG b (Const Void) (UnpreparedValue b), Maybe RemoteJoins)
 getRemoteJoinsAggregateSelect =
   second mapToNonEmpty . flip runState mempty . transformAggregateSelect mempty
 
 -- | Traverse through @'ConnectionSelect' and collect remote join fields (if any).
 getRemoteJoinsConnectionSelect
-  :: (Backend b)
+  :: Backend b
-  => ConnectionSelect b r (UnpreparedValue b)
+  => ConnectionSelect b (RemoteSelect UnpreparedValue) (UnpreparedValue b)
   -> (ConnectionSelect b (Const Void) (UnpreparedValue b), Maybe RemoteJoins)
 getRemoteJoinsConnectionSelect =
   second mapToNonEmpty . flip runState mempty . transformConnectionSelect mempty
 
 -- | Traverse through 'MutationOutput' and collect remote join fields (if any)
 getRemoteJoinsMutationOutput
-  :: (Backend b)
+  :: Backend b
-  => MutationOutputG b r (UnpreparedValue b)
+  => MutationOutputG b (RemoteSelect UnpreparedValue) (UnpreparedValue b)
   -> (MutationOutputG b (Const Void) (UnpreparedValue b), Maybe RemoteJoins)
 getRemoteJoinsMutationOutput =
   second mapToNonEmpty . flip runState mempty . transformMutationOutput mempty
@@ -111,15 +111,15 @@ getRemoteJoinsMutationOutput =
 -- local helpers
 
 getRemoteJoinsAnnFields
-  :: (Backend b)
+  :: Backend b
-  => AnnFieldsG b r (UnpreparedValue b)
+  => AnnFieldsG b (RemoteSelect UnpreparedValue) (UnpreparedValue b)
   -> (AnnFieldsG b (Const Void) (UnpreparedValue b), Maybe RemoteJoins)
 getRemoteJoinsAnnFields =
   second mapToNonEmpty . flip runState mempty . transformAnnFields mempty
 
 getRemoteJoinsMutationDB
-  :: (Backend b)
+  :: Backend b
-  => MutationDB b r (UnpreparedValue b)
+  => MutationDB b (RemoteSelect UnpreparedValue) (UnpreparedValue b)
   -> (MutationDB b (Const Void) (UnpreparedValue b), Maybe RemoteJoins)
 getRemoteJoinsMutationDB = \case
   MDBInsert insert ->
@@ -145,7 +145,7 @@ getRemoteJoinsMutationDB = \case
 
 getRemoteJoinsSyncAction
   :: (Backend b)
-  => AnnActionExecution b r (UnpreparedValue b)
+  => AnnActionExecution b (RemoteSelect UnpreparedValue) (UnpreparedValue b)
   -> (AnnActionExecution b (Const Void) (UnpreparedValue b), Maybe RemoteJoins)
 getRemoteJoinsSyncAction actionExecution =
   let (fields', remoteJoins) = getRemoteJoinsAnnFields $ _aaeFields actionExecution
@@ -153,7 +153,7 @@ getRemoteJoinsSyncAction actionExecution =
 
 getRemoteJoinsActionQuery
   :: (Backend b)
-  => ActionQuery b r (UnpreparedValue b)
+  => ActionQuery b (RemoteSelect UnpreparedValue) (UnpreparedValue b)
   -> (ActionQuery b (Const Void) (UnpreparedValue b), Maybe RemoteJoins)
 getRemoteJoinsActionQuery = \case
   AQQuery sync ->
@@ -180,7 +180,7 @@ getRemoteJoinsActionQuery = \case
 
 getRemoteJoinsActionMutation
   :: (Backend b)
-  => ActionMutation b r (UnpreparedValue b)
+  => ActionMutation b (RemoteSelect UnpreparedValue) (UnpreparedValue b)
   -> (ActionMutation b (Const Void) (UnpreparedValue b), Maybe RemoteJoins)
 getRemoteJoinsActionMutation = \case
   AMSync sync   -> first AMSync $ getRemoteJoinsSyncAction sync
@@ -190,7 +190,7 @@ getRemoteJoinsActionMutation = \case
 transformSelect
   :: (Backend b)
   => FieldPath
-  -> AnnSimpleSelectG b r (UnpreparedValue b)
+  -> AnnSimpleSelectG b (RemoteSelect UnpreparedValue) (UnpreparedValue b)
   -> State RemoteJoinMap (AnnSimpleSelectG b (Const Void) (UnpreparedValue b))
 transformSelect path sel = do
   let fields = _asnFields sel
@@ -201,7 +201,7 @@ transformSelect path sel = do
 transformAggregateSelect
   :: (Backend b)
   => FieldPath
-  -> AnnAggregateSelectG b r (UnpreparedValue b)
+  -> AnnAggregateSelectG b (RemoteSelect UnpreparedValue) (UnpreparedValue b)
   -> State RemoteJoinMap (AnnAggregateSelectG b (Const Void) (UnpreparedValue b))
 transformAggregateSelect path sel = do
   let aggFields = _asnFields sel
@@ -215,7 +215,7 @@ transformAggregateSelect path sel = do
 transformConnectionSelect
   :: (Backend b)
   => FieldPath
-  -> ConnectionSelect b r (UnpreparedValue b)
+  -> ConnectionSelect b (RemoteSelect UnpreparedValue) (UnpreparedValue b)
   -> State RemoteJoinMap (ConnectionSelect b (Const Void) (UnpreparedValue b))
 transformConnectionSelect path ConnectionSelect{..} = do
   let connectionFields = _asnFields _csSelect
@@ -238,7 +238,7 @@ transformConnectionSelect path ConnectionSelect{..} = do
 transformObjectSelect
   :: (Backend b)
   => FieldPath
-  -> AnnObjectSelectG b r (UnpreparedValue b)
+  -> AnnObjectSelectG b (RemoteSelect UnpreparedValue) (UnpreparedValue b)
   -> State RemoteJoinMap (AnnObjectSelectG b (Const Void) (UnpreparedValue b))
 transformObjectSelect path sel = do
   let fields = _aosFields sel
@@ -246,10 +246,9 @@ transformObjectSelect path sel = do
   pure sel{_aosFields = transformedFields}
 
 transformAnnFields
-  :: forall b r
+  :: forall b . Backend b
-   . (Backend b)
   => FieldPath
-  -> AnnFieldsG b r (UnpreparedValue b)
+  -> AnnFieldsG b (RemoteSelect UnpreparedValue) (UnpreparedValue b)
   -> State RemoteJoinMap (AnnFieldsG b (Const Void) (UnpreparedValue b))
 transformAnnFields path fields = do
 
@@ -260,9 +259,14 @@ transformAnnFields path fields = do
 
   let columnsInSelSet = HS.fromList $ map (pgiColumn . _acfInfo . snd) $ getFields _AFColumn fields
       scalarComputedFieldsInSelSet = HS.fromList $ map ((^. _2) . snd) $ getFields _AFComputedField fields
-      remoteSelects = getFields (_AFRemote) fields
+
+      remoteSelects = getFields (_AFRemote.to getRemoteSchemaSelect) fields
+      getRemoteSchemaSelect = \case
+        RemoteSelectRemoteSchema s -> s
+        RemoteSelectSource _s      -> error "remote source relationshsip found"
+
       remoteJoins = remoteSelects <&> \(fieldName, remoteSelect) ->
-        let RemoteSelect argsMap selSet hasuraFields remoteFields rsi = remoteSelect
+        let RemoteSchemaSelect argsMap selSet hasuraFields remoteFields rsi = remoteSelect
             hasuraFieldNames = HS.map dbJoinFieldToName hasuraFields
 
             -- See Note [Phantom fields in Remote Joins]
@@ -291,10 +295,11 @@ transformAnnFields path fields = do
         AFComputedField x n <$> case computedField of
           CFSScalar cfss cbe  -> pure $ CFSScalar cfss cbe
           CFSTable jas annSel -> CFSTable jas <$> transformSelect fieldPath annSel
-      AFRemote rs -> pure $ AFRemote rs
+      -- we generate this so that the response has a key with the relationship,
+      -- without which preserving the order of fields in the final response
+      -- would require a lot of bookkeeping
+      AFRemote _rs -> pure $ AFExpression "remote relationship placeholder"
       AFExpression t -> pure $ AFExpression t
-      -- TODO: implement this
-      AFDBRemote _ -> error "FIXME"
 
   case NE.nonEmpty remoteJoins of
     Nothing -> pure transformedFields

server/src-lib/Hasura/GraphQL/Explain.hs

@@ -53,7 +53,7 @@ explainQueryField
      )
   => UserInfo
   -> G.Name
-  -> QueryRootField UnpreparedValue UnpreparedValue
+  -> QueryRootField UnpreparedValue
   -> m EncJSON
 explainQueryField userInfo fieldName rootField = do
   case rootField of

server/src-lib/Hasura/GraphQL/Schema.hs

@@ -207,9 +207,9 @@ buildRoleContext
     getMutationRemotes = concatMap (concat . piMutation)
 
     buildSource :: forall b. BackendSchema b => SourceInfo b ->
-      ConcreteSchemaT m ( [FieldParser (P.ParseT Identity) (QueryRootField    UnpreparedValue UnpreparedValue)]
+      ConcreteSchemaT m ( [FieldParser (P.ParseT Identity) (QueryRootField    UnpreparedValue)]
-                        , [FieldParser (P.ParseT Identity) (MutationRootField UnpreparedValue UnpreparedValue)]
+                        , [FieldParser (P.ParseT Identity) (MutationRootField UnpreparedValue)]
-                        , [FieldParser (P.ParseT Identity) (MutationRootField UnpreparedValue UnpreparedValue)]
+                        , [FieldParser (P.ParseT Identity) (MutationRootField UnpreparedValue)]
                         )
     buildSource (SourceInfo sourceName tables functions sourceConfig) = do
       let validFunctions = takeValidFunctions functions
@@ -276,9 +276,9 @@ buildRelayRoleContext
 
   where
     buildSource :: forall b. BackendSchema b => SourceInfo b ->
-        ConcreteSchemaT m ( [FieldParser (P.ParseT Identity) (QueryRootField    UnpreparedValue UnpreparedValue)]
+        ConcreteSchemaT m ( [FieldParser (P.ParseT Identity) (QueryRootField    UnpreparedValue)]
-                          , [FieldParser (P.ParseT Identity) (MutationRootField UnpreparedValue UnpreparedValue)]
+                          , [FieldParser (P.ParseT Identity) (MutationRootField UnpreparedValue)]
-                          , [FieldParser (P.ParseT Identity) (MutationRootField UnpreparedValue UnpreparedValue)]
+                          , [FieldParser (P.ParseT Identity) (MutationRootField UnpreparedValue)]
                           )
     buildSource (SourceInfo sourceName tables functions sourceConfig) = do
       let validFunctions = takeValidFunctions functions
@@ -296,8 +296,8 @@ buildFullestDBSchema
   -> SourceCache
   -> [ActionInfo]
   -> NonObjectTypeMap
-  -> m (        Parser 'Output (P.ParseT Identity) (OMap.InsOrdHashMap G.Name (QueryRootField    UnpreparedValue UnpreparedValue))
+  -> m ( Parser 'Output (P.ParseT Identity) (OMap.InsOrdHashMap G.Name (QueryRootField UnpreparedValue))
-       , Maybe (Parser 'Output (P.ParseT Identity) (OMap.InsOrdHashMap G.Name (MutationRootField UnpreparedValue UnpreparedValue)))
+       , Maybe (Parser 'Output (P.ParseT Identity) (OMap.InsOrdHashMap G.Name (MutationRootField UnpreparedValue)))
        )
 buildFullestDBSchema queryContext sources allActionInfos nonObjectCustomTypes =
   runMonadSchema adminRoleName queryContext sources do
@@ -317,8 +317,8 @@ buildFullestDBSchema queryContext sources allActionInfos nonObjectCustomTypes =
 
   where
     buildSource :: forall b. BackendSchema b => SourceInfo b ->
-        ConcreteSchemaT m ( [FieldParser (P.ParseT Identity) (QueryRootField    UnpreparedValue UnpreparedValue)]
+        ConcreteSchemaT m ( [FieldParser (P.ParseT Identity) (QueryRootField    UnpreparedValue)]
-                          , [FieldParser (P.ParseT Identity) (MutationRootField UnpreparedValue UnpreparedValue)]
+                          , [FieldParser (P.ParseT Identity) (MutationRootField UnpreparedValue)]
                           )
     buildSource (SourceInfo sourceName tables functions sourceConfig) = do
       let validFunctions = takeValidFunctions functions
@@ -432,7 +432,7 @@ buildQueryFields
   -> SourceConfig b
   -> TableCache b
   -> FunctionCache b
-  -> m [P.FieldParser n (QueryRootField UnpreparedValue UnpreparedValue)]
+  -> m [P.FieldParser n (QueryRootField UnpreparedValue)]
 buildQueryFields sourceName sourceConfig tables (takeExposedAs FEAQuery -> functions) = do
   roleName <- askRoleName
   functionPermsCtx <- asks $ qcFunctionPermsContext . getter
@@ -459,7 +459,7 @@ buildRelayQueryFields
   -> SourceConfig b
   -> TableCache b
   -> FunctionCache b
-  -> m [P.FieldParser n (QueryRootField UnpreparedValue UnpreparedValue)]
+  -> m [P.FieldParser n (QueryRootField UnpreparedValue)]
 buildRelayQueryFields sourceName sourceConfig tables (takeExposedAs FEAQuery -> functions) = do
   tableConnectionFields <- for (Map.toList tables) \(tableName, tableInfo) -> runMaybeT do
     tableGQLName <- getTableGQLName @b tableInfo
@@ -484,7 +484,7 @@ buildMutationFields
   -> SourceConfig b
   -> TableCache b
   -> FunctionCache b
-  -> m [P.FieldParser n (MutationRootField UnpreparedValue UnpreparedValue)]
+  -> m [P.FieldParser n (MutationRootField UnpreparedValue)]
 buildMutationFields scenario sourceName sourceConfig tables (takeExposedAs FEAMutation -> functions) = do
   roleName <- askRoleName
   tableMutations <- for (Map.toList tables) \(tableName, tableInfo) -> do
@@ -540,13 +540,13 @@ buildQueryParser
      , MonadRole r m
      , Has QueryContext r
      )
-  => [P.FieldParser n (QueryRootField UnpreparedValue UnpreparedValue)]
+  => [P.FieldParser n (QueryRootField UnpreparedValue)]
   -> [P.FieldParser n RemoteField]
   -> [ActionInfo]
   -> NonObjectTypeMap
-  -> Maybe (Parser 'Output n (OMap.InsOrdHashMap G.Name (MutationRootField UnpreparedValue UnpreparedValue)))
+  -> Maybe (Parser 'Output n (OMap.InsOrdHashMap G.Name (MutationRootField UnpreparedValue)))
-  -> Parser 'Output n (OMap.InsOrdHashMap G.Name (QueryRootField UnpreparedValue UnpreparedValue))
+  -> Parser 'Output n (OMap.InsOrdHashMap G.Name (QueryRootField UnpreparedValue))
-  -> m (Parser 'Output n (OMap.InsOrdHashMap G.Name (QueryRootField UnpreparedValue UnpreparedValue)))
+  -> m (Parser 'Output n (OMap.InsOrdHashMap G.Name (QueryRootField UnpreparedValue)))
 buildQueryParser pgQueryFields remoteFields allActions nonObjectCustomTypes mutationParser subscriptionParser = do
   actionQueryFields <- concat <$> traverse (buildActionQueryFields nonObjectCustomTypes) allActions
   let allQueryFields = pgQueryFields <> actionQueryFields <> map (fmap RFRemote) remoteFields
@@ -554,10 +554,10 @@ buildQueryParser pgQueryFields remoteFields allActions nonObjectCustomTypes muta
 
 queryWithIntrospectionHelper
   :: forall n m. (MonadSchema n m, MonadError QErr m)
-  => [P.FieldParser n (QueryRootField UnpreparedValue UnpreparedValue)]
+  => [P.FieldParser n (QueryRootField UnpreparedValue)]
-  -> Maybe (Parser 'Output n (OMap.InsOrdHashMap G.Name (MutationRootField UnpreparedValue UnpreparedValue)))
+  -> Maybe (Parser 'Output n (OMap.InsOrdHashMap G.Name (MutationRootField UnpreparedValue)))
-  -> Parser 'Output n (OMap.InsOrdHashMap G.Name (QueryRootField UnpreparedValue UnpreparedValue))
+  -> Parser 'Output n (OMap.InsOrdHashMap G.Name (QueryRootField UnpreparedValue))
-  -> m (Parser 'Output n (OMap.InsOrdHashMap G.Name (QueryRootField UnpreparedValue UnpreparedValue)))
+  -> m (Parser 'Output n (OMap.InsOrdHashMap G.Name (QueryRootField UnpreparedValue)))
 queryWithIntrospectionHelper basicQueryFP mutationP subscriptionP = do
   basicQueryP <- queryRootFromFields basicQueryFP
   emptyIntro  <- emptyIntrospection
@@ -588,15 +588,15 @@ queryWithIntrospectionHelper basicQueryFP mutationP subscriptionP = do
 queryRootFromFields
   :: forall n m
    . (MonadError QErr m, MonadParse n)
-  => [P.FieldParser n (QueryRootField UnpreparedValue UnpreparedValue)]
+  => [P.FieldParser n (QueryRootField UnpreparedValue)]
-  -> m (Parser 'Output n (OMap.InsOrdHashMap G.Name (QueryRootField UnpreparedValue UnpreparedValue)))
+  -> m (Parser 'Output n (OMap.InsOrdHashMap G.Name (QueryRootField UnpreparedValue)))
 queryRootFromFields fps =
   P.safeSelectionSet queryRoot Nothing fps <&> fmap (fmap typenameToRawRF)
 
 emptyIntrospection
   :: forall m n
    . (MonadSchema n m, MonadError QErr m)
-  => m [P.FieldParser n (QueryRootField UnpreparedValue UnpreparedValue)]
+  => m [P.FieldParser n (QueryRootField UnpreparedValue)]
 emptyIntrospection = do
   emptyQueryP <- queryRootFromFields @n []
   introspectionTypes <- collectTypes (P.parserType emptyQueryP)
@@ -630,9 +630,9 @@ buildSubscriptionParser
      , MonadRole r m
      , Has QueryContext r
      )
-  => [P.FieldParser n (QueryRootField UnpreparedValue UnpreparedValue)]
+  => [P.FieldParser n (QueryRootField UnpreparedValue)]
   -> [ActionInfo]
-  -> m (Parser 'Output n (OMap.InsOrdHashMap G.Name (QueryRootField UnpreparedValue UnpreparedValue)))
+  -> m (Parser 'Output n (OMap.InsOrdHashMap G.Name (QueryRootField UnpreparedValue)))
 buildSubscriptionParser queryFields allActions = do
   actionSubscriptionFields <- concat <$> traverse buildActionSubscriptionFields allActions
   let subscriptionFields = queryFields <> actionSubscriptionFields
@@ -648,8 +648,8 @@ buildMutationParser
   => [P.FieldParser n RemoteField]
   -> [ActionInfo]
   -> NonObjectTypeMap
-  -> [P.FieldParser n (MutationRootField UnpreparedValue UnpreparedValue)]
+  -> [P.FieldParser n (MutationRootField UnpreparedValue)]
-  -> m (Maybe (Parser 'Output n (OMap.InsOrdHashMap G.Name (MutationRootField UnpreparedValue UnpreparedValue))))
+  -> m (Maybe (Parser 'Output n (OMap.InsOrdHashMap G.Name (MutationRootField UnpreparedValue))))
 buildMutationParser allRemotes allActions nonObjectCustomTypes mutationFields = do
   actionParsers <- concat <$> traverse (buildActionMutationFields nonObjectCustomTypes) allActions
   let mutationFieldsParser =

server/src-lib/Hasura/GraphQL/Schema/Action.hs

@@ -47,7 +47,7 @@ actionExecute
    . MonadBuildSchema ('Postgres 'Vanilla) r m n
   => NonObjectTypeMap
   -> ActionInfo
-  -> m (Maybe (FieldParser n (AnnActionExecution ('Postgres 'Vanilla) UnpreparedValue (UnpreparedValue ('Postgres 'Vanilla)))))
+  -> m (Maybe (FieldParser n (AnnActionExecution ('Postgres 'Vanilla) (RQL.RemoteSelect UnpreparedValue) (UnpreparedValue ('Postgres 'Vanilla)))))
 actionExecute nonObjectTypeMap actionInfo = runMaybeT do
   roleName <- askRoleName
   guard (roleName == adminRoleName || roleName `Map.member` permissions)
@@ -113,7 +113,7 @@ actionAsyncQuery
   :: forall r m n
    . MonadBuildSchema ('Postgres 'Vanilla) r m n
   => ActionInfo
-  -> m (Maybe (FieldParser n (AnnActionAsyncQuery ('Postgres 'Vanilla) UnpreparedValue (UnpreparedValue ('Postgres 'Vanilla)))))
+  -> m (Maybe (FieldParser n (AnnActionAsyncQuery ('Postgres 'Vanilla) (RQL.RemoteSelect UnpreparedValue) (UnpreparedValue ('Postgres 'Vanilla)))))
 actionAsyncQuery actionInfo = runMaybeT do
   roleName <- askRoleName
   guard $ roleName == adminRoleName || roleName `Map.member` permissions
@@ -172,7 +172,7 @@ actionOutputFields
    . MonadBuildSchema ('Postgres 'Vanilla) r m n
   => G.GType
   -> AnnotatedObjectType
-  -> m (Parser 'Output n (RQL.AnnFieldsG ('Postgres 'Vanilla) UnpreparedValue (UnpreparedValue ('Postgres 'Vanilla))))
+  -> m (Parser 'Output n (AnnotatedFields ('Postgres 'Vanilla)))
 actionOutputFields outputType annotatedObject = do
   let outputObject = _aotDefinition annotatedObject
       scalarOrEnumFields = map outputFieldParser $ toList $ _otdFields outputObject
@@ -194,7 +194,7 @@ actionOutputFields outputType annotatedObject = do
 
     outputFieldParser
       :: ObjectFieldDefinition (G.GType, AnnotatedObjectFieldType)
-      -> FieldParser n (RQL.AnnFieldG ('Postgres 'Vanilla) UnpreparedValue (UnpreparedValue ('Postgres 'Vanilla)))
+      -> FieldParser n (AnnotatedField ('Postgres 'Vanilla))
     outputFieldParser (ObjectFieldDefinition name _ description (gType, objectFieldType)) =
       let fieldName   = unObjectFieldName name
           selection   = P.selection_ fieldName description $ case objectFieldType of
@@ -211,7 +211,7 @@ actionOutputFields outputType annotatedObject = do
 
     relationshipFieldParser
       :: TypeRelationship (TableInfo ('Postgres 'Vanilla)) (ColumnInfo ('Postgres 'Vanilla))
-      -> m (Maybe [FieldParser n (RQL.AnnFieldG ('Postgres 'Vanilla) UnpreparedValue (UnpreparedValue ('Postgres 'Vanilla)))])
+      -> m (Maybe [FieldParser n (AnnotatedField ('Postgres 'Vanilla))])
     relationshipFieldParser (TypeRelationship relName relType sourceName tableInfo fieldMapping) = runMaybeT do
       let tableName     = _tciName $ _tiCoreInfo tableInfo
           fieldName     = unRelationshipName relName

server/src-lib/Hasura/GraphQL/Schema/Backend.hs

@@ -72,7 +72,7 @@ class Backend b => BackendSchema (b :: BackendType) where
     -> TableInfo b
     -> G.Name
     -> SelPermInfo b
-    -> m [FieldParser n (QueryRootField UnpreparedValue UnpreparedValue)]
+    -> m [FieldParser n (QueryRootField UnpreparedValue)]
   buildTableRelayQueryFields
     :: MonadBuildSchema b r m n
     => SourceName
@@ -82,7 +82,7 @@ class Backend b => BackendSchema (b :: BackendType) where
     -> G.Name
     -> NESeq (ColumnInfo b)
     -> SelPermInfo b
-    -> m [FieldParser n (QueryRootField UnpreparedValue UnpreparedValue)]
+    -> m [FieldParser n (QueryRootField UnpreparedValue)]
   buildTableInsertMutationFields
     :: MonadBuildSchema b r m n
     => SourceName
@@ -93,7 +93,7 @@ class Backend b => BackendSchema (b :: BackendType) where
     -> InsPermInfo b
     -> Maybe (SelPermInfo b)
     -> Maybe (UpdPermInfo b)
-    -> m [FieldParser n (MutationRootField UnpreparedValue UnpreparedValue)]
+    -> m [FieldParser n (MutationRootField UnpreparedValue)]
   buildTableUpdateMutationFields
     :: MonadBuildSchema b r m n
     => SourceName
@@ -103,7 +103,7 @@ class Backend b => BackendSchema (b :: BackendType) where
     -> G.Name
     -> UpdPermInfo b
     -> Maybe (SelPermInfo b)
-    -> m [FieldParser n (MutationRootField UnpreparedValue UnpreparedValue)]
+    -> m [FieldParser n (MutationRootField UnpreparedValue)]
   buildTableDeleteMutationFields
     :: MonadBuildSchema b r m n
     => SourceName
@@ -113,7 +113,7 @@ class Backend b => BackendSchema (b :: BackendType) where
     -> G.Name
     -> DelPermInfo b
     -> Maybe (SelPermInfo b)
-    -> m [FieldParser n (MutationRootField UnpreparedValue UnpreparedValue)]
+    -> m [FieldParser n (MutationRootField UnpreparedValue)]
   buildFunctionQueryFields
     :: MonadBuildSchema b r m n
     => SourceName
@@ -122,7 +122,7 @@ class Backend b => BackendSchema (b :: BackendType) where
     -> FunctionInfo b
     -> TableName b
     -> SelPermInfo b
-    -> m [FieldParser n (QueryRootField UnpreparedValue UnpreparedValue)]
+    -> m [FieldParser n (QueryRootField UnpreparedValue)]
   buildFunctionRelayQueryFields
     :: MonadBuildSchema b r m n
     => SourceName
@@ -132,7 +132,7 @@ class Backend b => BackendSchema (b :: BackendType) where
     -> TableName b
     -> NESeq (ColumnInfo b)
     -> SelPermInfo b
-    -> m [FieldParser n (QueryRootField UnpreparedValue UnpreparedValue)]
+    -> m [FieldParser n (QueryRootField UnpreparedValue)]
   buildFunctionMutationFields
     :: MonadBuildSchema b r m n
     => SourceName
@@ -141,7 +141,7 @@ class Backend b => BackendSchema (b :: BackendType) where
     -> FunctionInfo b
     -> TableName b
     -> SelPermInfo b
-    -> m [FieldParser n (MutationRootField UnpreparedValue UnpreparedValue)]
+    -> m [FieldParser n (MutationRootField UnpreparedValue)]
 
   -- table components
   tableArguments

server/src-lib/Hasura/GraphQL/Schema/Build.hs

@@ -30,7 +30,7 @@ buildTableQueryFields
   -> TableInfo b
   -> G.Name
   -> SelPermInfo b
-  -> m [FieldParser n (QueryRootField UnpreparedValue UnpreparedValue)]
+  -> m [FieldParser n (QueryRootField UnpreparedValue)]
 buildTableQueryFields sourceName sourceInfo tableName tableInfo gqlName selPerms = do
   let
     mkRF = RFDB sourceName
@@ -64,7 +64,7 @@ buildTableInsertMutationFields
   -> InsPermInfo b
   -> Maybe (SelPermInfo b)
   -> Maybe (UpdPermInfo b)
-  -> m [FieldParser n (MutationRootField UnpreparedValue UnpreparedValue)]
+  -> m [FieldParser n (MutationRootField UnpreparedValue)]
 buildTableInsertMutationFields sourceName sourceInfo tableName tableInfo gqlName insPerms mSelPerms mUpdPerms = do
   let
     mkRF = RFDB sourceName
@@ -96,7 +96,7 @@ buildTableUpdateMutationFields
   -> G.Name
   -> UpdPermInfo b
   -> Maybe (SelPermInfo b)
-  -> m [FieldParser n (MutationRootField UnpreparedValue UnpreparedValue)]
+  -> m [FieldParser n (MutationRootField UnpreparedValue)]
 buildTableUpdateMutationFields sourceName sourceInfo tableName tableInfo gqlName updPerms mSelPerms = do
   let
     mkRF = RFDB sourceName
@@ -127,7 +127,7 @@ buildTableDeleteMutationFields
   -> G.Name
   -> DelPermInfo b
   -> Maybe (SelPermInfo b)
-  -> m [FieldParser n (MutationRootField UnpreparedValue UnpreparedValue)]
+  -> m [FieldParser n (MutationRootField UnpreparedValue)]
 buildTableDeleteMutationFields sourceName sourceInfo tableName tableInfo gqlName delPerms mSelPerms = do
   let
     mkRF = RFDB sourceName
@@ -157,7 +157,7 @@ buildFunctionQueryFields
   -> FunctionInfo b
   -> TableName b
   -> SelPermInfo b
-  -> m [FieldParser n (QueryRootField UnpreparedValue UnpreparedValue)]
+  -> m [FieldParser n (QueryRootField UnpreparedValue)]
 buildFunctionQueryFields sourceName sourceInfo functionName functionInfo tableName selPerms = do
   funcName <- functionGraphQLName @b functionName `onLeft` throwError
   let
@@ -188,7 +188,7 @@ buildFunctionMutationFields
   -> FunctionInfo b
   -> TableName b
   -> SelPermInfo b
-  -> m [FieldParser n (MutationRootField UnpreparedValue UnpreparedValue)]
+  -> m [FieldParser n (MutationRootField UnpreparedValue)]
 buildFunctionMutationFields sourceName sourceInfo functionName functionInfo tableName selPerms = do
   funcName <- functionGraphQLName @b functionName `onLeft` throwError
   let

server/src-lib/Hasura/GraphQL/Schema/Common.hs

@@ -21,13 +21,15 @@ import           Hasura.GraphQL.Parser              (UnpreparedValue)
 import           Hasura.RQL.Types
 
 
-type SelectExp           b = IR.AnnSimpleSelectG    b UnpreparedValue (UnpreparedValue b)
+type SelectExp           b = IR.AnnSimpleSelectG    b (IR.RemoteSelect UnpreparedValue) (UnpreparedValue b)
-type AggSelectExp        b = IR.AnnAggregateSelectG b UnpreparedValue (UnpreparedValue b)
+type AggSelectExp        b = IR.AnnAggregateSelectG b (IR.RemoteSelect UnpreparedValue) (UnpreparedValue b)
-type ConnectionSelectExp b = IR.ConnectionSelect    b UnpreparedValue (UnpreparedValue b)
+type ConnectionSelectExp b = IR.ConnectionSelect    b (IR.RemoteSelect UnpreparedValue) (UnpreparedValue b)
-type SelectArgs          b = IR.SelectArgsG         b                 (UnpreparedValue b)
+type SelectArgs          b = IR.SelectArgsG         b                                   (UnpreparedValue b)
-type TablePerms          b = IR.TablePermG          b                 (UnpreparedValue b)
+type TablePerms          b = IR.TablePermG          b                                   (UnpreparedValue b)
-type AnnotatedFields     b = IR.AnnFieldsG          b UnpreparedValue (UnpreparedValue b)
+type AnnotatedFields     b = IR.AnnFieldsG          b (IR.RemoteSelect UnpreparedValue) (UnpreparedValue b)
-type AnnotatedField      b = IR.AnnFieldG           b UnpreparedValue (UnpreparedValue b)
+type AnnotatedField      b = IR.AnnFieldG           b (IR.RemoteSelect UnpreparedValue) (UnpreparedValue b)
+type ConnectionFields    b = IR.ConnectionFields    b (IR.RemoteSelect UnpreparedValue) (UnpreparedValue b)
+type EdgeFields          b = IR.EdgeFields          b (IR.RemoteSelect UnpreparedValue) (UnpreparedValue b)
 
 data QueryContext =
   QueryContext

server/src-lib/Hasura/GraphQL/Schema/Mutation.hs

@@ -22,6 +22,7 @@ import qualified Hasura.GraphQL.Parser         as P
 import qualified Hasura.RQL.IR.Delete          as IR
 import qualified Hasura.RQL.IR.Insert          as IR
 import qualified Hasura.RQL.IR.Returning       as IR
+import qualified Hasura.RQL.IR.Select          as IR
 import qualified Hasura.RQL.IR.Update          as IR
 
 import           Hasura.GraphQL.Parser         (FieldParser, InputFieldsParser, Kind (..), Parser,
@@ -48,7 +49,7 @@ insertIntoTable
   -> InsPermInfo b          -- ^ insert permissions of the table
   -> Maybe (SelPermInfo b)  -- ^ select permissions of the table (if any)
   -> Maybe (UpdPermInfo b)  -- ^ update permissions of the table (if any)
-  -> m (FieldParser n (IR.AnnInsert b UnpreparedValue (UnpreparedValue b)))
+  -> m (FieldParser n (IR.AnnInsert b (IR.RemoteSelect UnpreparedValue) (UnpreparedValue b)))
 insertIntoTable sourceName tableInfo fieldName description insertPerms selectPerms updatePerms = do
   let columns = tableColumns tableInfo
   selectionParser <- mutationSelectionSet sourceName tableInfo selectPerms
@@ -86,7 +87,7 @@ insertOneIntoTable
   -> InsPermInfo b          -- ^ insert permissions of the table
   -> SelPermInfo b          -- ^ select permissions of the table
   -> Maybe (UpdPermInfo b)  -- ^ update permissions of the table (if any)
-  -> m (FieldParser n (IR.AnnInsert b UnpreparedValue (UnpreparedValue b)))
+  -> m (FieldParser n (IR.AnnInsert b (IR.RemoteSelect UnpreparedValue) (UnpreparedValue b)))
 insertOneIntoTable sourceName tableInfo fieldName description insertPerms selectPerms updatePerms = do
   let columns = tableColumns tableInfo
   selectionParser <- tableSelectionSet sourceName tableInfo selectPerms
@@ -298,7 +299,7 @@ updateTable
   -> Maybe G.Description      -- ^ field description, if any
   -> UpdPermInfo b            -- ^ update permissions of the table
   -> Maybe (SelPermInfo b)    -- ^ select permissions of the table (if any)
-  -> m (Maybe (FieldParser n (IR.AnnUpdG b UnpreparedValue (UnpreparedValue b))))
+  -> m (Maybe (FieldParser n (IR.AnnUpdG b (IR.RemoteSelect UnpreparedValue) (UnpreparedValue b))))
 updateTable sourceName tableInfo fieldName description updatePerms selectPerms = runMaybeT $ do
   let whereName = $$(G.litName "where")
       whereDesc = "filter the rows which have to be updated"
@@ -324,7 +325,7 @@ updateTableByPk
   -> Maybe G.Description  -- ^ field description, if any
   -> UpdPermInfo b        -- ^ update permissions of the table
   -> SelPermInfo b        -- ^ select permissions of the table
-  -> m (Maybe (FieldParser n (IR.AnnUpdG b UnpreparedValue (UnpreparedValue b))))
+  -> m (Maybe (FieldParser n (IR.AnnUpdG b (IR.RemoteSelect UnpreparedValue) (UnpreparedValue b))))
 updateTableByPk sourceName tableInfo fieldName description updatePerms selectPerms = runMaybeT $ do
   tableGQLName <- getTableGQLName tableInfo
   let columns = tableColumns tableInfo
@@ -350,9 +351,9 @@ mkUpdateObject
   -> ( ( [(Column b, IR.UpdOpExpG (UnpreparedValue b))]
        , AnnBoolExp b (UnpreparedValue b)
        )
-     , IR.MutationOutputG b UnpreparedValue (UnpreparedValue b)
+     , IR.MutationOutputG b (IR.RemoteSelect UnpreparedValue) (UnpreparedValue b)
      )
-  -> IR.AnnUpdG b UnpreparedValue (UnpreparedValue b)
+  -> IR.AnnUpdG b (IR.RemoteSelect UnpreparedValue) (UnpreparedValue b)
 mkUpdateObject table columns updatePerms ((opExps, whereExp), mutationOutput) =
   IR.AnnUpd { IR.uqp1Table   = table
             , IR.uqp1OpExps  = opExps
@@ -379,7 +380,7 @@ deleteFromTable
   -> Maybe G.Description    -- ^ field description, if any
   -> DelPermInfo b          -- ^ delete permissions of the table
   -> Maybe (SelPermInfo b)  -- ^ select permissions of the table (if any)
-  -> m (FieldParser n (IR.AnnDelG b UnpreparedValue (UnpreparedValue b)))
+  -> m (FieldParser n (IR.AnnDelG b (IR.RemoteSelect UnpreparedValue) (UnpreparedValue b)))
 deleteFromTable sourceName tableInfo fieldName description deletePerms selectPerms = do
   let whereName = $$(G.litName "where")
       whereDesc = "filter the rows which have to be deleted"
@@ -401,7 +402,7 @@ deleteFromTableByPk
   -> Maybe G.Description  -- ^ field description, if any
   -> DelPermInfo b        -- ^ delete permissions of the table
   -> SelPermInfo b        -- ^ select permissions of the table
-  -> m (Maybe (FieldParser n (IR.AnnDelG b UnpreparedValue (UnpreparedValue b))))
+  -> m (Maybe (FieldParser n (IR.AnnDelG b (IR.RemoteSelect UnpreparedValue) (UnpreparedValue b))))
 deleteFromTableByPk sourceName tableInfo fieldName description deletePerms selectPerms = runMaybeT $ do
   let columns = tableColumns tableInfo
   pkArgs    <- MaybeT $ primaryKeysArguments tableInfo selectPerms
@@ -414,8 +415,8 @@ mkDeleteObject
   => TableName b
   -> [ColumnInfo b]
   -> DelPermInfo b
-  -> (AnnBoolExp b (UnpreparedValue b), IR.MutationOutputG b UnpreparedValue (UnpreparedValue b))
+  -> (AnnBoolExp b (UnpreparedValue b), IR.MutationOutputG b (IR.RemoteSelect UnpreparedValue) (UnpreparedValue b))
-  -> IR.AnnDelG b UnpreparedValue (UnpreparedValue b)
+  -> IR.AnnDelG b (IR.RemoteSelect UnpreparedValue) (UnpreparedValue b)
 mkDeleteObject table columns deletePerms (whereExp, mutationOutput) =
   IR.AnnDel { IR.dqp1Table   = table
             , IR.dqp1Where   = (permissionFilter, whereExp)
@@ -436,7 +437,7 @@ mutationSelectionSet
   => SourceName
   -> TableInfo b
   -> Maybe (SelPermInfo b)
-  -> m (Parser 'Output n (IR.MutFldsG b UnpreparedValue (UnpreparedValue b)))
+  -> m (Parser 'Output n (IR.MutFldsG b (IR.RemoteSelect UnpreparedValue) (UnpreparedValue b)))
 mutationSelectionSet sourceName tableInfo selectPerms =
   memoizeOn 'mutationSelectionSet (sourceName, tableName) do
   tableGQLName <- getTableGQLName tableInfo

server/src-lib/Hasura/GraphQL/Schema/Postgres.hs

@@ -20,7 +20,7 @@ buildActionQueryFields
   :: MonadBuildSchema ('Postgres 'Vanilla) r m n
   => NonObjectTypeMap
   -> ActionInfo
-  -> m [FieldParser n (QueryRootField UnpreparedValue UnpreparedValue)]
+  -> m [FieldParser n (QueryRootField UnpreparedValue)]
 buildActionQueryFields nonObjectCustomTypes actionInfo =
   maybeToList <$> case _adType (_aiDefinition actionInfo) of
     ActionQuery                       ->
@@ -33,7 +33,7 @@ buildActionMutationFields
   :: MonadBuildSchema ('Postgres 'Vanilla) r m n
   => NonObjectTypeMap
   -> ActionInfo
-  -> m [FieldParser n (MutationRootField UnpreparedValue UnpreparedValue)]
+  -> m [FieldParser n (MutationRootField UnpreparedValue)]
 buildActionMutationFields nonObjectCustomTypes actionInfo =
   maybeToList <$> case _adType (_aiDefinition actionInfo) of
     ActionQuery -> pure Nothing
@@ -45,8 +45,7 @@ buildActionMutationFields nonObjectCustomTypes actionInfo =
 buildActionSubscriptionFields
   :: MonadBuildSchema ('Postgres 'Vanilla) r m n
   => ActionInfo
-  -> m [FieldParser n (QueryRootField UnpreparedValue
+  -> m [FieldParser n (QueryRootField UnpreparedValue)]
-                       UnpreparedValue)]
 buildActionSubscriptionFields actionInfo =
   maybeToList <$> case _adType (_aiDefinition actionInfo) of
     ActionQuery                       -> pure Nothing

server/src-lib/Hasura/GraphQL/Schema/Select.hs

@@ -398,7 +398,7 @@ tableConnectionSelectionSet
   => SourceName
   -> TableInfo b
   -> SelPermInfo b
-  -> m (Parser 'Output n (IR.ConnectionFields b UnpreparedValue (UnpreparedValue b)))
+  -> m (Parser 'Output n (ConnectionFields b))
 tableConnectionSelectionSet sourceName tableInfo selectPermissions = memoizeOn 'tableConnectionSelectionSet (sourceName, tableName) do
   tableGQLName <- getTableGQLName tableInfo
   edgesParser  <- tableEdgesSelectionSet tableGQLName
@@ -432,7 +432,7 @@ tableConnectionSelectionSet sourceName tableInfo selectPermissions = memoizeOn '
          <&> parsedSelectionsToFields IR.PageInfoTypename
 
     tableEdgesSelectionSet
-      :: G.Name -> m (Parser 'Output n (IR.EdgeFields b UnpreparedValue (UnpreparedValue b)))
+      :: G.Name -> m (Parser 'Output n (EdgeFields b))
     tableEdgesSelectionSet tableGQLName = do
       edgeNodeParser      <- P.nonNullableParser <$> tableSelectionSet sourceName tableInfo selectPermissions
       let edgesType = tableGQLName <> $$(G.litName "Edge")
@@ -1155,7 +1155,7 @@ remoteRelationshipField remoteFieldInfo = runMaybeT do
             `P.bindField` \G.Field{ G._fArguments = args, G._fSelectionSet = selSet } -> do
               let remoteArgs =
                     Map.toList args <&> \(argName, argVal) -> IR.RemoteFieldArgument argName $ P.GraphQLValue $ argVal
-              pure $ IR.AFRemote $ IR.RemoteSelect
+              pure $ IR.AFRemote $ IR.RemoteSelectRemoteSchema $ IR.RemoteSchemaSelect
                 { _rselArgs          = remoteArgs
                 , _rselSelection     = selSet
                 , _rselHasuraFields  = _rfiHasuraFields remoteSchema
@@ -1410,7 +1410,7 @@ nodePG = memoizeOn 'nodePG () do
 nodeField
   :: forall m n r
    . MonadBuildSchema ('Postgres 'Vanilla) r m n
-  => m (P.FieldParser n (IR.QueryRootField UnpreparedValue UnpreparedValue))
+  => m (P.FieldParser n (IR.QueryRootField UnpreparedValue))
 nodeField = do
   let idDescription = G.Description "A globally unique id"
       idArgument = P.field $$(G.litName "id") (Just idDescription) P.identifier

server/src-lib/Hasura/GraphQL/Transport/HTTP.hs

@@ -167,7 +167,7 @@ runSessVarPred = filterSessionVariables . unSessVarPred
 -- | Filter out only those session variables used by the query AST provided
 filterVariablesFromQuery
   :: Backend backend
-  => [RootField (QueryDBRoot UnpreparedValue UnpreparedValue) RemoteField (ActionQuery backend UnpreparedValue (UnpreparedValue backend)) d]
+  => [RootField (QueryDBRoot (RemoteSelect UnpreparedValue) UnpreparedValue) RemoteField (ActionQuery backend (RemoteSelect UnpreparedValue) (UnpreparedValue backend)) d]
   -> SessVarPred
 filterVariablesFromQuery query = fold $ rootToSessVarPreds =<< query
   where

server/src-lib/Hasura/RQL/IR/Root.hs

@@ -72,7 +72,14 @@ data ActionMutation (b :: BackendType) (r :: BackendType -> Type) v
 newtype QueryDBRoot    r v b = QDBR (QueryDB    b r (v b))
 newtype MutationDBRoot r v b = MDBR (MutationDB b r (v b))
 
+-- | Represents a query root field to an action
+type QueryActionRoot v
+  = ActionQuery ('Postgres 'Vanilla) (RemoteSelect v) (v ('Postgres 'Vanilla))
 
-type QueryRootField        r v = RootField (QueryDBRoot    r v) RQL.RemoteField (ActionQuery    ('Postgres 'Vanilla) r (v ('Postgres 'Vanilla))) JO.Value
+-- | Represents a mutation root field to an action
-type MutationRootField     r v = RootField (MutationDBRoot r v) RQL.RemoteField (ActionMutation ('Postgres 'Vanilla) r (v ('Postgres 'Vanilla))) JO.Value
+type MutationActionRoot v
-type SubscriptionRootField r v = RootField (QueryDBRoot    r v) Void            Void                                                             Void
+  = ActionMutation ('Postgres 'Vanilla) (RemoteSelect v) (v ('Postgres 'Vanilla))
+
+type QueryRootField        v = RootField (QueryDBRoot    (RemoteSelect v) v) RQL.RemoteField (QueryActionRoot v)    JO.Value
+type MutationRootField     v = RootField (MutationDBRoot (RemoteSelect v) v) RQL.RemoteField (MutationActionRoot v) JO.Value
+type SubscriptionRootField v = RootField (QueryDBRoot    (RemoteSelect v) v) Void            Void                   Void

server/src-lib/Hasura/RQL/IR/Select.hs

@@ -188,8 +188,11 @@ data AnnFieldG (b :: BackendType) (r :: BackendType -> Type) v
   | AFObjectRelation !(ObjectRelationSelectG b r v)
   | AFArrayRelation !(ArraySelectG b r v)
   | AFComputedField !(XComputedField b) !ComputedFieldName !(ComputedFieldSelect b r v)
-  | AFRemote !(RemoteSelect b)
+  -- | A relationship to a remote source/remote schema. Its kind is
-  | AFDBRemote !(AB.AnyBackend (DBRemoteSelect b r))
+  -- (r :: BackendType -> Type) so that AFRemote can capture something
+  -- that is specific to the backend AnnFieldG. See RemoteSelect. When
+  -- remote joins are extracted from the structure, 'r' becomes 'Const Void'
+  | AFRemote !(r b)
   | AFNodeId !(XRelay b) !(TableName b) !(PrimaryKeyColumns b)
   | AFExpression !Text
   deriving (Functor, Foldable, Traversable)
@@ -361,7 +364,7 @@ type ArraySelect b = ArraySelectG b (Const Void) (SQLExpression b)
 type ArraySelectFieldsG b r v = Fields (ArraySelectG b r v)
 
 
--- Remote schema relationship
+-- Remote schema relationships
 
 data RemoteFieldArgument
   = RemoteFieldArgument
@@ -369,8 +372,8 @@ data RemoteFieldArgument
   , _rfaValue    :: !(InputValue RemoteSchemaVariable)
   } deriving (Eq,Show)
 
-data RemoteSelect (b :: BackendType)
+data RemoteSchemaSelect (b :: BackendType)
-  = RemoteSelect
+  = RemoteSchemaSelect
   { _rselArgs         :: ![RemoteFieldArgument]
   , _rselSelection    :: !(G.SelectionSet G.NoFragments RemoteSchemaVariable)
   , _rselHasuraFields :: !(HashSet (DBJoinField b))
@@ -378,16 +381,45 @@ data RemoteSelect (b :: BackendType)
   , _rselRemoteSchema :: !RemoteSchemaInfo
   }
 
+-- | Captures the selection set of a remote source relationship.
+data SourceRelationshipSelection
+    (b :: BackendType)
+    (r :: BackendType -> Type)
+    (vf :: BackendType -> Type)
+  = SourceRelationshipObject !(AnnObjectSelectG b r (vf b))
+  | SourceRelationshipArray !(AnnSimpleSelectG b r (vf b))
+  | SourceRelationshipArrayAggregate !(AnnAggregateSelectG b r (vf b))
 
--- Remote db relationship
+-- | A relationship to a remote source. 'vf' (could use a better name) is
-
+-- analogous to 'v' in other IR types such as 'AnnFieldG'. vf's kind is
-data DBRemoteSelect (src :: BackendType) (r :: BackendType -> Type) (tgt :: BackendType)
+-- (BackendType -> Type) instead of v's 'Type' so that 'v' of 'AnnFieldG' can
-  = DBRemoteSelect
+-- be specific to the backend that it captures ('b' of an AnnFieldG changes as
-  { _dbrselHasuraColumns :: ![(ColumnInfo src, ColumnInfo tgt)]
+-- we walk down the IR branches which capture relationships to other databases)
-  , _dbrselTargetQuery   :: !(QueryDB tgt r (r tgt))
+data RemoteSourceSelect
-  , _dbrselTargetConfig  :: !(SourceConfig tgt)
+    (src :: BackendType)
-  }
+    (vf :: BackendType -> Type)
+    (tgt :: BackendType)
+  = RemoteSourceSelect
+    { _rssSourceName   :: !SourceName
+    , _rssSourceConfig :: !(SourceConfig tgt)
+    , _rssSelection    :: !(SourceRelationshipSelection tgt (RemoteSelect vf) vf)
+    , _rssJoinMapping  :: !(HM.HashMap FieldName (ColumnInfo src, ScalarType tgt, Column tgt))
+    -- ^ Additional information about the source's join columns:
+    -- (ColumnInfo src) so that we can add the join column to the AST
+    -- (ScalarType tgt) so that the remote can interpret the join values coming
+    -- from src
+    -- (Column tgt) so that an appropriate join condition / IN clause can be built
+    -- by the remote
+    }
 
+-- | A remote relationship to either a remote schema or a remote source.
+-- See RemoteSourceSelect for explanation on 'vf'.
+data RemoteSelect
+    (vf :: BackendType -> Type)
+    (src :: BackendType)
+  = RemoteSelectRemoteSchema !(RemoteSchemaSelect src)
+  -- ^ AnyBackend is used here to capture a relationship to an arbitrary target
+  | RemoteSelectSource !(AB.AnyBackend (RemoteSourceSelect src vf))
 
 -- Permissions