graphql-engine/server/src-lib/Hasura/Backends/Postgres/Translate/Select/Internal/Process.hs

-- | This module defines functions that translate from the Postgres IR into
-- Postgres SQL AST.
--
-- NOTE: These functions 'processAnnAggregateSelect', 'processAnnSimpleSelect',
-- 'processConnectionSelect', are all mutually recursive.
--
-- These functions are generally called from the top level functions in
-- Translate.Select, and the call stack looks like:
--
--     * 'selectQuerySQL' -> 'mkSQLSelect' -> 'processAnnSimpleSelect' -> 'processSelectParams'/'processAnnFields'
--
--     * 'selectAggregateQuerySQL' -> 'mkAggregateSelect' -> 'processAnnAggregateSelect' -> 'processSelectParams'/'processAnnFields'
--
--     * 'connetionSelectQuerySQL' -> 'mkConnectionSelect' -> 'processConnectionSelection' -> 'processSelectParams'
--
-- 'SelectSource' consists of a prefix, a source, a boolean conditional
-- expression, and info on whether sorting or slicing is done (needed to handle
-- the LIMIT optimisation)
module Hasura.Backends.Postgres.Translate.Select.Internal.Process
  ( processAnnAggregateSelect,
    processAnnSimpleSelect,
    processConnectionSelect,
  )
where

import Data.HashMap.Strict qualified as HashMap
import Data.List.NonEmpty qualified as NE
import Data.Text.Extended (ToTxt (toTxt))
import Hasura.Backends.Postgres.SQL.DML qualified as S
import Hasura.Backends.Postgres.SQL.Types
  ( IsIdentifier (toIdentifier),
    PGCol (..),
    QualifiedObject (QualifiedObject),
    QualifiedTable,
    SchemaName (getSchemaTxt),
    TableIdentifier (..),
    identifierToTableIdentifier,
    qualifiedObjectToText,
    tableIdentifierToIdentifier,
  )
import Hasura.Backends.Postgres.Translate.BoolExp (toSQLBoolExp)
import Hasura.Backends.Postgres.Translate.Column (toJSONableExp)
import Hasura.Backends.Postgres.Translate.Select.AnnotatedFieldJSON
import Hasura.Backends.Postgres.Translate.Select.Internal.Aliases
  ( contextualizeBaseTableColumn,
    mkAnnOrderByAlias,
    mkArrayRelationAlias,
    mkArrayRelationSourcePrefix,
    mkBaseTableIdentifier,
    mkComputedFieldTableIdentifier,
    mkObjectRelationTableAlias,
    mkOrderByFieldName,
  )
import Hasura.Backends.Postgres.Translate.Select.Internal.Extractor
  ( aggregateFieldsToExtractorExps,
    asJsonAggExtr,
    withJsonAggExtr,
  )
import Hasura.Backends.Postgres.Translate.Select.Internal.Helpers
  ( cursorIdentifier,
    cursorsSelectAliasIdentifier,
    encodeBase64,
    endCursorIdentifier,
    fromTableRowArgs,
    hasNextPageIdentifier,
    hasPreviousPageIdentifier,
    nativeQueryNameToAlias,
    pageInfoSelectAliasIdentifier,
    selectFromToFromItem,
    startCursorIdentifier,
    withForceAggregation,
  )
import Hasura.Backends.Postgres.Translate.Select.Internal.JoinTree
  ( withWriteArrayConnection,
    withWriteArrayRelation,
    withWriteComputedFieldTableSet,
    withWriteObjectRelation,
  )
import Hasura.Backends.Postgres.Translate.Select.Internal.OrderBy (processOrderByItems)
import Hasura.Backends.Postgres.Translate.Types
import Hasura.GraphQL.Schema.NamingCase (NamingCase)
import Hasura.GraphQL.Schema.Node (currentNodeIdVersion, nodeIdVersionInt)
import Hasura.NativeQuery.IR (NativeQuery (..))
import Hasura.Prelude
import Hasura.RQL.IR.BoolExp
import Hasura.RQL.IR.OrderBy (OrderByItemG (OrderByItemG, obiColumn))
import Hasura.RQL.IR.Select
import Hasura.RQL.Types.Backend
import Hasura.RQL.Types.BackendType
import Hasura.RQL.Types.Column
import Hasura.RQL.Types.Common
import Hasura.RQL.Types.Relationships.Local
import Hasura.RQL.Types.Schema.Options qualified as Options

processSelectParams ::
  forall pgKind m.
  ( MonadReader Options.StringifyNumbers m,
    MonadWriter SelectWriter m,
    Backend ('Postgres pgKind)
  ) =>
  SourcePrefixes ->
  FieldName ->
  SimilarArrayFields ->
  SelectFrom ('Postgres pgKind) ->
  PermissionLimitSubQuery ->
  TablePerm ('Postgres pgKind) ->
  SelectArgs ('Postgres pgKind) ->
  m
    ( SelectSource,
      [(S.ColumnAlias, S.SQLExp)],
      Maybe S.SQLExp -- Order by cursor
    )
processSelectParams
  sourcePrefixes
  fieldAlias
  similarArrFields
  selectFrom
  permLimitSubQ
  tablePermissions
  tableArgs = do
    (additionalExtrs, selectSorting, cursorExp) <-
      processOrderByItems (identifierToTableIdentifier thisSourcePrefix) fieldAlias similarArrFields distM orderByM
    whereSource <- selectFromToQual selectFrom
    let fromItem = selectFromToFromItem (identifierToTableIdentifier $ _pfBase sourcePrefixes) selectFrom
        finalWhere =
          toSQLBoolExp whereSource $
            maybe permFilter (andAnnBoolExps permFilter) whereM
        sortingAndSlicing = SortingAndSlicing selectSorting selectSlicing
        selectSource =
          SelectSource
            thisSourcePrefix
            fromItem
            finalWhere
            sortingAndSlicing
    pure
      ( selectSource,
        additionalExtrs,
        cursorExp
      )
    where
      thisSourcePrefix = _pfThis sourcePrefixes
      SelectArgs whereM orderByM inpLimitM offsetM distM = tableArgs
      TablePerm permFilter permLimit = tablePermissions
      selectSlicing = SelectSlicing finalLimit offsetM
      finalLimit =
        -- if sub query is required, then only use input limit
        --    because permission limit is being applied in subquery
        -- else compare input and permission limits
        case permLimitSubQ of
          PLSQRequired _ -> inpLimitM
          PLSQNotRequired -> compareLimits

      compareLimits =
        case (inpLimitM, permLimit) of
          (inpLim, Nothing) -> inpLim
          (Nothing, permLim) -> permLim
          (Just inp, Just perm) -> Just (min inp perm)

      -- You should be able to retrieve this information
      -- from the FromItem generated with selectFromToFromItem
      -- however given from S.FromItem is modelled, it is not
      -- possible currently.
      --
      -- More precisely, 'selectFromToFromItem' is injective but not surjective, so
      -- any S.FromItem -> S.Qual function would have to be partial.
      selectFromToQual :: SelectFrom ('Postgres pgKind) -> m S.Qual
      selectFromToQual = \case
        FromTable table -> pure $ S.QualTable table
        FromIdentifier i -> pure $ S.QualifiedIdentifier (TableIdentifier $ unFIIdentifier i) Nothing
        FromFunction qf _ _ -> pure $ S.QualifiedIdentifier (TableIdentifier $ qualifiedObjectToText qf) Nothing
        FromStoredProcedure {} -> error "selectFromToQual: FromStoredProcedure"
        FromNativeQuery nq -> do
          -- we are going to cram our SQL in a CTE, and this is what we will call it
          let cteName = nativeQueryNameToAlias (nqRootFieldName nq)

          -- emit the query itself to the Writer
          tell $
            mempty
              { _swCustomSQLCTEs =
                  CustomSQLCTEs (HashMap.singleton cteName (nqInterpolatedQuery nq))
              }

          pure $ S.QualifiedIdentifier (S.tableAliasToIdentifier cteName) Nothing

processAnnAggregateSelect ::
  forall pgKind m.
  ( MonadReader Options.StringifyNumbers m,
    MonadWriter SelectWriter m,
    Backend ('Postgres pgKind),
    PostgresAnnotatedFieldJSON pgKind
  ) =>
  SourcePrefixes ->
  FieldName ->
  AnnAggregateSelect ('Postgres pgKind) ->
  m
    ( SelectSource,
      HashMap.HashMap S.ColumnAlias S.SQLExp,
      S.Extractor
    )
processAnnAggregateSelect sourcePrefixes fieldAlias annAggSel = do
  (selectSource, orderByAndDistinctExtrs, _) <-
    processSelectParams
      sourcePrefixes
      fieldAlias
      similarArrayFields
      tableFrom
      permLimitSubQuery
      tablePermissions
      tableArgs
  let thisSourcePrefix = identifierToTableIdentifier $ _pfThis sourcePrefixes
  processedFields <- forM aggSelFields $ \(fieldName, field) ->
    (fieldName,)
      <$> case field of
        TAFAgg aggFields ->
          pure
            ( aggregateFieldsToExtractorExps thisSourcePrefix aggFields,
              aggregateFieldToExp aggFields strfyNum
            )
        TAFNodes _ annFields -> do
          annFieldExtr <- processAnnFields thisSourcePrefix fieldName similarArrayFields annFields tCase
          pure
            ( [annFieldExtr],
              withJsonAggExtr permLimitSubQuery (orderByForJsonAgg selectSource) $
                S.toColumnAlias $
                  toIdentifier fieldName
            )
        TAFExp e ->
          pure
            ( [],
              withForceAggregation S.textTypeAnn $ S.SELit e
            )

  let topLevelExtractor =
        flip S.Extractor (Just $ S.toColumnAlias $ toIdentifier fieldAlias) $
          S.applyJsonBuildObj $
            flip concatMap (map (second snd) processedFields) $
              \(FieldName fieldText, fieldExp) -> [S.SELit fieldText, fieldExp]
      nodeExtractors =
        HashMap.fromList $
          concatMap (fst . snd) processedFields <> orderByAndDistinctExtrs

  pure (selectSource, nodeExtractors, topLevelExtractor)
  where
    AnnSelectG aggSelFields tableFrom tablePermissions tableArgs strfyNum tCase = annAggSel
    permLimit = _tpLimit tablePermissions
    orderBy = _saOrderBy tableArgs
    permLimitSubQuery = mkPermissionLimitSubQuery permLimit aggSelFields orderBy
    similarArrayFields = HashMap.unions $
      flip map (map snd aggSelFields) $ \case
        TAFAgg _ -> mempty
        TAFNodes _ annFlds ->
          mkSimilarArrayFields annFlds orderBy
        TAFExp _ -> mempty

    mkPermissionLimitSubQuery ::
      Maybe Int ->
      TableAggregateFields ('Postgres pgKind) ->
      Maybe (NE.NonEmpty (AnnotatedOrderByItem ('Postgres pgKind))) ->
      PermissionLimitSubQuery
    mkPermissionLimitSubQuery permLimit' aggFields orderBys =
      case permLimit' of
        Nothing -> PLSQNotRequired
        Just limit ->
          if hasAggregateField || hasAggOrderBy
            then PLSQRequired limit
            else PLSQNotRequired
      where
        hasAggregateField = flip any (map snd aggFields) $
          \case
            TAFAgg _ -> True
            _ -> False

        hasAggOrderBy = case orderBys of
          Nothing -> False
          Just l -> flip any (concatMap toList $ toList l) $
            \case
              AOCArrayAggregation {} -> True
              _ -> False

processAnnFields ::
  forall pgKind m.
  ( MonadReader Options.StringifyNumbers m,
    MonadWriter SelectWriter m,
    Backend ('Postgres pgKind),
    PostgresAnnotatedFieldJSON pgKind
  ) =>
  TableIdentifier ->
  FieldName ->
  SimilarArrayFields ->
  AnnFields ('Postgres pgKind) ->
  Maybe NamingCase ->
  m (S.ColumnAlias, S.SQLExp)
processAnnFields sourcePrefix fieldAlias similarArrFields annFields tCase = do
  fieldExps <- forM annFields $ \(fieldName, field) ->
    (fieldName,)
      <$> case field of
        AFExpression t -> pure $ S.SELit t
        AFNodeId _ sn tn pKeys -> pure $ mkNodeId sn tn pKeys
        AFColumn c -> toSQLCol c
        AFObjectRelation objSel -> withWriteObjectRelation $ do
          let AnnRelationSelectG relName relMapping annObjSel = objSel
              AnnObjectSelectG objAnnFields target targetFilter = annObjSel
              objRelSourcePrefix = mkObjectRelationTableAlias sourcePrefix relName
              sourcePrefixes = mkSourcePrefixes objRelSourcePrefix
          annFieldsExtr <- processAnnFields (identifierToTableIdentifier $ _pfThis sourcePrefixes) fieldName HashMap.empty objAnnFields tCase
          case target of
            FromNativeQuery nq -> do
              let cteName = nativeQueryNameToAlias (nqRootFieldName nq)

                  nativeQueryIdentifier = S.tableAliasToIdentifier cteName

              -- emit the query itself to the Writer
              tell $
                mempty
                  { _swCustomSQLCTEs =
                      CustomSQLCTEs (HashMap.singleton cteName (nqInterpolatedQuery nq))
                  }

              let selectSource =
                    ObjectSelectSource
                      (_pfThis sourcePrefixes)
                      (S.FIIdentifier nativeQueryIdentifier)
                      (toSQLBoolExp (S.QualifiedIdentifier nativeQueryIdentifier Nothing) targetFilter)
                  objRelSource = ObjectRelationSource relName relMapping selectSource
              pure
                ( objRelSource,
                  HashMap.fromList [annFieldsExtr],
                  S.mkQIdenExp objRelSourcePrefix fieldName
                )
            FromTable tableFrom -> do
              let selectSource =
                    ObjectSelectSource
                      (_pfThis sourcePrefixes)
                      (S.FISimple tableFrom Nothing)
                      (toSQLBoolExp (S.QualTable tableFrom) targetFilter)
                  objRelSource = ObjectRelationSource relName relMapping selectSource
              pure
                ( objRelSource,
                  HashMap.fromList [annFieldsExtr],
                  S.mkQIdenExp objRelSourcePrefix fieldName
                )
            other -> error $ "processAnnFields: " <> show other
        AFArrayRelation arrSel -> do
          let arrRelSourcePrefix = mkArrayRelationSourcePrefix sourcePrefix fieldAlias similarArrFields fieldName
              arrRelAlias = mkArrayRelationAlias fieldAlias similarArrFields fieldName
          processArrayRelation (mkSourcePrefixes arrRelSourcePrefix) fieldName arrRelAlias arrSel tCase
          pure $ S.mkQIdenExp arrRelSourcePrefix fieldName
        AFComputedField _ _ (CFSScalar scalar caseBoolExpMaybe) -> do
          computedFieldSQLExp <- fromScalarComputedField scalar
          -- The computed field is conditionally outputed depending
          -- on the presence of `caseBoolExpMaybe` and the value it
          -- evaluates to. `caseBoolExpMaybe` will be set only in the
          -- case of an inherited role.
          -- See [SQL generation for inherited role]
          case caseBoolExpMaybe of
            Nothing -> pure computedFieldSQLExp
            Just caseBoolExp ->
              let boolExp =
                    S.simplifyBoolExp $
                      toSQLBoolExp (S.QualifiedIdentifier baseTableIdentifier Nothing) $
                        _accColCaseBoolExpField <$> caseBoolExp
               in pure $ S.SECond boolExp computedFieldSQLExp S.SENull
        AFComputedField _ _ (CFSTable selectTy sel) -> withWriteComputedFieldTableSet $ do
          let computedFieldSourcePrefix =
                mkComputedFieldTableIdentifier sourcePrefix fieldName
          (selectSource, nodeExtractors) <-
            processAnnSimpleSelect
              (mkSourcePrefixes computedFieldSourcePrefix)
              fieldName
              PLSQNotRequired
              sel
          let computedFieldTableSetSource = ComputedFieldTableSetSource fieldName selectSource
              extractor =
                asJsonAggExtr selectTy (S.toColumnAlias fieldName) PLSQNotRequired $
                  orderByForJsonAgg selectSource
          pure
            ( computedFieldTableSetSource,
              extractor,
              nodeExtractors,
              S.mkQIdenExp computedFieldSourcePrefix fieldName
            )

  pure $ annRowToJson @pgKind fieldAlias fieldExps
  where
    mkSourcePrefixes newPrefix = SourcePrefixes (tableIdentifierToIdentifier newPrefix) (tableIdentifierToIdentifier sourcePrefix)

    baseTableIdentifier = mkBaseTableIdentifier sourcePrefix

    toSQLCol :: AnnColumnField ('Postgres pgKind) S.SQLExp -> m S.SQLExp
    toSQLCol (AnnColumnField col typ asText colOpM caseBoolExpMaybe) = do
      strfyNum <- ask
      let sqlExpression =
            withColumnOp colOpM $
              S.mkQIdenExp baseTableIdentifier col
          finalSQLExpression =
            -- Check out [SQL generation for inherited role]
            case caseBoolExpMaybe of
              Nothing -> sqlExpression
              Just caseBoolExp ->
                let boolExp =
                      S.simplifyBoolExp $
                        toSQLBoolExp (S.QualifiedIdentifier baseTableIdentifier Nothing) $
                          _accColCaseBoolExpField <$> caseBoolExp
                 in S.SECond boolExp sqlExpression S.SENull
      pure $ toJSONableExp strfyNum typ asText tCase finalSQLExpression

    fromScalarComputedField :: ComputedFieldScalarSelect ('Postgres pgKind) S.SQLExp -> m S.SQLExp
    fromScalarComputedField computedFieldScalar = do
      strfyNum <- ask
      pure $
        toJSONableExp strfyNum (ColumnScalar ty) False Nothing $
          withColumnOp colOpM $
            S.SEFunction $
              S.FunctionExp fn (fromTableRowArgs sourcePrefix args) Nothing
      where
        ComputedFieldScalarSelect fn args ty colOpM = computedFieldScalar

    withColumnOp :: Maybe S.ColumnOp -> S.SQLExp -> S.SQLExp
    withColumnOp colOpM sqlExp = case colOpM of
      Nothing -> sqlExp
      Just (S.ColumnOp opText cExp) -> S.mkSQLOpExp opText sqlExp cExp

    mkNodeId :: SourceName -> QualifiedTable -> PrimaryKeyColumns ('Postgres pgKind) -> S.SQLExp
    mkNodeId _sourceName (QualifiedObject tableSchema tableName) pkeyColumns =
      let columnInfoToSQLExp pgColumnInfo =
            toJSONableExp Options.Don'tStringifyNumbers (ciType pgColumnInfo) False Nothing $
              S.mkQIdenExp (mkBaseTableIdentifier sourcePrefix) $
                ciColumn pgColumnInfo
       in -- See Note [Relay Node id].
          encodeBase64 $
            flip S.SETyAnn S.textTypeAnn $
              S.applyJsonBuildArray $
                [ S.intToSQLExp $ nodeIdVersionInt currentNodeIdVersion,
                  S.SELit (getSchemaTxt tableSchema),
                  S.SELit (toTxt tableName)
                ]
                  <> map columnInfoToSQLExp (toList pkeyColumns)

mkSimilarArrayFields ::
  forall pgKind v.
  (Backend ('Postgres pgKind), Eq v) =>
  AnnFieldsG ('Postgres pgKind) Void v ->
  Maybe (NE.NonEmpty (AnnotatedOrderByItemG ('Postgres pgKind) v)) ->
  SimilarArrayFields
mkSimilarArrayFields annFields maybeOrderBys =
  HashMap.fromList $
    flip map allTuples $
      \(relNameAndArgs, fieldName) -> (fieldName, getSimilarFields relNameAndArgs)
  where
    getSimilarFields relNameAndArgs = map snd $ filter ((== relNameAndArgs) . fst) allTuples
    allTuples = arrayRelationTuples <> aggOrderByRelationTuples
    arrayRelationTuples =
      let arrayFields = mapMaybe getAnnArr annFields
       in flip map arrayFields $
            \(f, relSel) -> (getArrayRelNameAndSelectArgs relSel, f)

    getAnnArr ::
      (a, AnnFieldG ('Postgres pgKind) r v) ->
      Maybe (a, ArraySelectG ('Postgres pgKind) r v)
    getAnnArr (f, annFld) = case annFld of
      AFArrayRelation (ASConnection _) -> Nothing
      AFArrayRelation ar -> Just (f, ar)
      _ -> Nothing

    aggOrderByRelationTuples =
      let mkItem (relName, fieldName) =
            ( (relName, noSelectArgs),
              fieldName
            )
       in map mkItem $
            maybe
              []
              (mapMaybe (fetchAggOrderByRels . obiColumn) . toList)
              maybeOrderBys

    fetchAggOrderByRels (AOCArrayAggregation ri _ _) =
      Just (riName ri, mkOrderByFieldName $ riName ri)
    fetchAggOrderByRels _ = Nothing

    getArrayRelNameAndSelectArgs ::
      ArraySelectG ('Postgres pgKind) r v ->
      (RelName, SelectArgsG ('Postgres pgKind) v)
    getArrayRelNameAndSelectArgs = \case
      ASSimple r -> (_aarRelationshipName r, _asnArgs $ _aarAnnSelect r)
      ASAggregate r -> (_aarRelationshipName r, _asnArgs $ _aarAnnSelect r)
      ASConnection r -> (_aarRelationshipName r, _asnArgs $ _csSelect $ _aarAnnSelect r)

processArrayRelation ::
  forall pgKind m.
  ( MonadReader Options.StringifyNumbers m,
    MonadWriter SelectWriter m,
    Backend ('Postgres pgKind),
    PostgresAnnotatedFieldJSON pgKind
  ) =>
  SourcePrefixes ->
  FieldName ->
  S.TableAlias ->
  ArraySelect ('Postgres pgKind) ->
  Maybe NamingCase ->
  m ()
processArrayRelation sourcePrefixes fieldAlias relAlias arrSel _tCase =
  case arrSel of
    ASSimple annArrRel -> withWriteArrayRelation $ do
      let AnnRelationSelectG _ colMapping sel = annArrRel
          permLimitSubQuery =
            maybe PLSQNotRequired PLSQRequired $ _tpLimit $ _asnPerm sel
      (source, nodeExtractors) <-
        processAnnSimpleSelect sourcePrefixes fieldAlias permLimitSubQuery sel
      let topExtr =
            asJsonAggExtr
              JASMultipleRows
              (S.toColumnAlias fieldAlias)
              permLimitSubQuery
              $ orderByForJsonAgg source
      pure
        ( ArrayRelationSource relAlias colMapping source,
          topExtr,
          nodeExtractors,
          ()
        )
    ASAggregate aggSel -> withWriteArrayRelation $ do
      let AnnRelationSelectG _ colMapping sel = aggSel
      (source, nodeExtractors, topExtr) <-
        processAnnAggregateSelect sourcePrefixes fieldAlias sel
      pure
        ( ArrayRelationSource relAlias colMapping source,
          topExtr,
          nodeExtractors,
          ()
        )
    ASConnection connSel -> withWriteArrayConnection $ do
      let AnnRelationSelectG _ colMapping sel = connSel
      (source, topExtractor, nodeExtractors) <-
        processConnectionSelect sourcePrefixes fieldAlias relAlias colMapping sel
      pure
        ( source,
          topExtractor,
          nodeExtractors,
          ()
        )

aggregateFieldToExp :: AggregateFields ('Postgres pgKind) -> Options.StringifyNumbers -> S.SQLExp
aggregateFieldToExp aggFlds strfyNum = jsonRow
  where
    jsonRow = S.applyJsonBuildObj (concatMap aggToFlds aggFlds)
    withAls fldName sqlExp = [S.SELit fldName, sqlExp]
    aggToFlds (FieldName t, fld) = withAls t $ case fld of
      AFCount cty -> S.SECount cty
      AFOp aggOp -> aggOpToObj aggOp
      AFExp e -> S.SELit e

    aggOpToObj (AggregateOp opText flds) =
      S.applyJsonBuildObj $ concatMap (colFldsToExtr opText) flds

    colFldsToExtr opText (FieldName t, CFCol col ty) =
      [ S.SELit t,
        toJSONableExp strfyNum ty False Nothing $
          S.SEFnApp opText [S.SEIdentifier $ toIdentifier col] Nothing
      ]
    colFldsToExtr _ (FieldName t, CFExp e) =
      [S.SELit t, S.SELit e]

processAnnSimpleSelect ::
  forall pgKind m.
  ( MonadReader Options.StringifyNumbers m,
    MonadWriter SelectWriter m,
    Backend ('Postgres pgKind),
    PostgresAnnotatedFieldJSON pgKind
  ) =>
  SourcePrefixes ->
  FieldName ->
  PermissionLimitSubQuery ->
  AnnSimpleSelect ('Postgres pgKind) ->
  m
    ( SelectSource,
      HashMap.HashMap S.ColumnAlias S.SQLExp
    )
processAnnSimpleSelect sourcePrefixes fieldAlias permLimitSubQuery annSimpleSel = do
  (selectSource, orderByAndDistinctExtrs, _) <-
    processSelectParams
      sourcePrefixes
      fieldAlias
      similarArrayFields
      tableFrom
      permLimitSubQuery
      tablePermissions
      tableArgs
  annFieldsExtr <-
    processAnnFields
      (identifierToTableIdentifier $ _pfThis sourcePrefixes)
      fieldAlias
      similarArrayFields
      annSelFields
      tCase
  let allExtractors = HashMap.fromList $ annFieldsExtr : orderByAndDistinctExtrs
  pure (selectSource, allExtractors)
  where
    AnnSelectG annSelFields tableFrom tablePermissions tableArgs _ tCase = annSimpleSel
    similarArrayFields =
      mkSimilarArrayFields annSelFields $ _saOrderBy tableArgs

processConnectionSelect ::
  forall pgKind m.
  ( MonadReader Options.StringifyNumbers m,
    MonadWriter SelectWriter m,
    Backend ('Postgres pgKind),
    PostgresAnnotatedFieldJSON pgKind
  ) =>
  SourcePrefixes ->
  FieldName ->
  S.TableAlias ->
  HashMap.HashMap PGCol PGCol ->
  ConnectionSelect ('Postgres pgKind) Void S.SQLExp ->
  m
    ( ArrayConnectionSource,
      S.Extractor,
      HashMap.HashMap S.ColumnAlias S.SQLExp
    )
processConnectionSelect sourcePrefixes fieldAlias relAlias colMapping connectionSelect = do
  (selectSource, orderByAndDistinctExtrs, maybeOrderByCursor) <-
    processSelectParams
      sourcePrefixes
      fieldAlias
      similarArrayFields
      selectFrom
      permLimitSubQuery
      tablePermissions
      tableArgs

  let mkCursorExtractor = (S.toColumnAlias cursorIdentifier,) . (`S.SETyAnn` S.textTypeAnn)
      cursorExtractors = case maybeOrderByCursor of
        Just orderByCursor -> [mkCursorExtractor orderByCursor]
        Nothing ->
          -- Extract primary key columns from base select along with cursor expression.
          -- Those columns are required to perform connection split via a WHERE clause.
          mkCursorExtractor primaryKeyColumnsObjectExp : primaryKeyColumnExtractors
  (topExtractorExp, exps) <- flip runStateT [] $ processFields selectSource
  let topExtractor = S.Extractor topExtractorExp $ Just $ S.toColumnAlias fieldIdentifier
      allExtractors = HashMap.fromList $ cursorExtractors <> exps <> orderByAndDistinctExtrs
      arrayConnectionSource =
        ArrayConnectionSource
          relAlias
          colMapping
          (mkSplitBoolExp <$> maybeSplit)
          maybeSlice
          selectSource
  pure
    ( arrayConnectionSource,
      topExtractor,
      allExtractors
    )
  where
    ConnectionSelect _ primaryKeyColumns maybeSplit maybeSlice select = connectionSelect
    AnnSelectG fields selectFrom tablePermissions tableArgs _ tCase = select
    fieldIdentifier = toIdentifier fieldAlias
    thisPrefix = identifierToTableIdentifier $ _pfThis sourcePrefixes
    permLimitSubQuery = PLSQNotRequired

    primaryKeyColumnsObjectExp =
      S.applyJsonBuildObj $
        flip concatMap (toList primaryKeyColumns) $
          \pgColumnInfo ->
            [ S.SELit $ getPGColTxt $ ciColumn pgColumnInfo,
              toJSONableExp Options.Don'tStringifyNumbers (ciType pgColumnInfo) False tCase $
                S.mkQIdenExp (mkBaseTableIdentifier thisPrefix) $
                  ciColumn pgColumnInfo
            ]

    primaryKeyColumnExtractors =
      flip map (toList primaryKeyColumns) $
        \pgColumnInfo ->
          let pgColumn = ciColumn pgColumnInfo
           in ( contextualizeBaseTableColumn thisPrefix pgColumn,
                S.mkQIdenExp (mkBaseTableIdentifier thisPrefix) pgColumn
              )

    mkSplitBoolExp (firstSplit NE.:| rest) =
      S.BEBin S.OrOp (mkSplitCompareExp firstSplit) $ mkBoolExpFromRest firstSplit rest
      where
        mkBoolExpFromRest previousSplit =
          S.BEBin S.AndOp (mkEqualityCompareExp previousSplit) . \case
            [] -> S.BELit False
            (thisSplit : remainingSplit) -> mkSplitBoolExp (thisSplit NE.:| remainingSplit)

        mkSplitCompareExp (ConnectionSplit kind v (OrderByItemG obTyM obCol _)) =
          let obAlias = mkAnnOrderByAlias thisPrefix fieldAlias similarArrayFields obCol
              obTy = fromMaybe S.OTAsc obTyM
              compareOp = case (kind, obTy) of
                (CSKAfter, S.OTAsc) -> S.SGT
                (CSKAfter, S.OTDesc) -> S.SLT
                (CSKBefore, S.OTAsc) -> S.SLT
                (CSKBefore, S.OTDesc) -> S.SGT
           in S.BECompare compareOp (S.SEIdentifier $ toIdentifier obAlias) v

        mkEqualityCompareExp (ConnectionSplit _ v orderByItem) =
          let obAlias =
                mkAnnOrderByAlias thisPrefix fieldAlias similarArrayFields $
                  obiColumn orderByItem
           in S.BECompare S.SEQ (S.SEIdentifier $ toIdentifier obAlias) v

    similarArrayFields = HashMap.unions $
      flip map (map snd fields) $ \case
        ConnectionTypename {} -> mempty
        ConnectionPageInfo {} -> mempty
        ConnectionEdges edges -> HashMap.unions $
          flip map (map snd edges) $ \case
            EdgeTypename {} -> mempty
            EdgeCursor {} -> mempty
            EdgeNode annFields ->
              mkSimilarArrayFields annFields $ _saOrderBy tableArgs

    mkSimpleJsonAgg rowExp ob =
      let jsonAggExp = S.SEFnApp "json_agg" [rowExp] ob
       in S.SEFnApp "coalesce" [jsonAggExp, S.SELit "[]"] Nothing

    processFields ::
      forall n.
      ( MonadReader Options.StringifyNumbers n,
        MonadWriter SelectWriter n,
        MonadState [(S.ColumnAlias, S.SQLExp)] n
      ) =>
      SelectSource ->
      n S.SQLExp
    processFields selectSource =
      fmap (S.applyJsonBuildObj . concat) $
        forM fields $
          \(FieldName fieldText, field) ->
            (S.SELit fieldText :) . pure
              <$> case field of
                ConnectionTypename t -> pure $ withForceAggregation S.textTypeAnn $ S.SELit t
                ConnectionPageInfo pageInfoFields -> pure $ processPageInfoFields pageInfoFields
                ConnectionEdges edges ->
                  fmap (flip mkSimpleJsonAgg (orderByForJsonAgg selectSource) . S.applyJsonBuildObj . concat) $
                    forM edges $
                      \(FieldName edgeText, edge) ->
                        (S.SELit edgeText :) . pure
                          <$> case edge of
                            EdgeTypename t -> pure $ S.SELit t
                            EdgeCursor -> pure $ encodeBase64 $ S.SEIdentifier (toIdentifier cursorIdentifier)
                            EdgeNode annFields -> do
                              let edgeFieldName =
                                    FieldName $
                                      getFieldNameTxt fieldAlias <> "." <> fieldText <> "." <> edgeText
                                  edgeFieldIdentifier = toIdentifier edgeFieldName
                              annFieldsExtrExp <- processAnnFields thisPrefix edgeFieldName similarArrayFields annFields tCase
                              modify' (<> [annFieldsExtrExp])
                              pure $ S.SEIdentifier edgeFieldIdentifier

    processPageInfoFields infoFields =
      S.applyJsonBuildObj $
        flip concatMap infoFields $
          \(FieldName fieldText, field) -> (:) (S.SELit fieldText) $ pure case field of
            PageInfoTypename t -> withForceAggregation S.textTypeAnn $ S.SELit t
            PageInfoHasNextPage ->
              withForceAggregation S.boolTypeAnn $
                mkSingleFieldSelect (S.SEIdentifier hasNextPageIdentifier) pageInfoSelectAliasIdentifier
            PageInfoHasPreviousPage ->
              withForceAggregation S.boolTypeAnn $
                mkSingleFieldSelect (S.SEIdentifier hasPreviousPageIdentifier) pageInfoSelectAliasIdentifier
            PageInfoStartCursor ->
              withForceAggregation S.textTypeAnn $
                encodeBase64 $
                  mkSingleFieldSelect (S.SEIdentifier startCursorIdentifier) cursorsSelectAliasIdentifier
            PageInfoEndCursor ->
              withForceAggregation S.textTypeAnn $
                encodeBase64 $
                  mkSingleFieldSelect (S.SEIdentifier endCursorIdentifier) cursorsSelectAliasIdentifier
      where
        mkSingleFieldSelect field fromIdentifier =
          S.SESelect
            S.mkSelect
              { S.selExtr = [S.Extractor field Nothing],
                S.selFrom = Just $ S.FromExp [S.FIIdentifier fromIdentifier]
              }