graphql-engine/server/src-lib/Hasura/RQL/DDL/Schema/Cache.hs

{-# LANGUAGE Arrows               #-}
{-# LANGUAGE OverloadedLabels     #-}
{-# LANGUAGE UndecidableInstances #-}

{-| Top-level functions concerned specifically with operations on the schema cache, such as
rebuilding it from the catalog and incorporating schema changes. See the module documentation for
"Hasura.RQL.DDL.Schema" for more details.

__Note__: this module is __mutually recursive__ with other @Hasura.RQL.DDL.Schema.*@ modules, which
both define pieces of the implementation of building the schema cache and define handlers that
trigger schema cache rebuilds. -}
module Hasura.RQL.DDL.Schema.Cache
  ( RebuildableSchemaCache
  , lastBuiltSchemaCache
  , buildRebuildableSchemaCache
  , buildRebuildableSchemaCacheWithReason
  , CacheRWT
  , runCacheRWT

  , withMetadataCheck
  ) where

import           Hasura.Prelude

import qualified Data.Environment                         as Env
import qualified Data.HashMap.Strict.Extended             as M
import qualified Data.HashMap.Strict.InsOrd               as OMap
import qualified Data.HashSet                             as HS
import qualified Data.HashSet.InsOrd                      as HSIns
import qualified Database.PG.Query                        as Q

import           Control.Arrow.Extended
import           Control.Lens                             hiding ((.=))
import           Control.Monad.Trans.Control              (MonadBaseControl)
import           Control.Monad.Unique
import           Data.Aeson
import           Data.Text.Extended
import           Network.HTTP.Client.Extended

import qualified Hasura.Incremental                       as Inc
import qualified Hasura.Tracing                           as Tracing

import           Hasura.Backends.Postgres.Connection
import           Hasura.Backends.Postgres.SQL.Types
import           Hasura.GraphQL.Execute.Types
import           Hasura.GraphQL.Schema                    (buildGQLContext)
import           Hasura.Metadata.Class
import           Hasura.RQL.DDL.Action
import           Hasura.RQL.DDL.CustomTypes
import           Hasura.RQL.DDL.Deps
import           Hasura.RQL.DDL.EventTrigger
import           Hasura.RQL.DDL.RemoteSchema
import           Hasura.RQL.DDL.RemoteSchema.Permission   (resolveRoleBasedRemoteSchema)
import           Hasura.RQL.DDL.ScheduledTrigger
import           Hasura.RQL.DDL.Schema.Cache.Common
import           Hasura.RQL.DDL.Schema.Cache.Dependencies
import           Hasura.RQL.DDL.Schema.Cache.Fields
import           Hasura.RQL.DDL.Schema.Cache.Permission
import           Hasura.RQL.DDL.Schema.Common
import           Hasura.RQL.DDL.Schema.Diff
import           Hasura.RQL.DDL.Schema.Function
import           Hasura.RQL.DDL.Schema.Source
import           Hasura.RQL.DDL.Schema.Table
import           Hasura.RQL.Types                         hiding (fmFunction, tmTable)
import           Hasura.Server.Version                    (HasVersion)
import           Hasura.Session


buildRebuildableSchemaCache
  :: (HasVersion)
  => Env.Environment
  -> Metadata
  -> CacheBuild RebuildableSchemaCache
buildRebuildableSchemaCache =
  buildRebuildableSchemaCacheWithReason CatalogSync

buildRebuildableSchemaCacheWithReason
  :: (HasVersion)
  => BuildReason
  -> Env.Environment
  -> Metadata
  -> CacheBuild RebuildableSchemaCache
buildRebuildableSchemaCacheWithReason reason env metadata = do
  result <- flip runReaderT reason $
    Inc.build (buildSchemaCacheRule env) (metadata, initialInvalidationKeys)
  pure $ RebuildableSchemaCache (Inc.result result) initialInvalidationKeys (Inc.rebuildRule result)

newtype CacheRWT m a
  -- The CacheInvalidations component of the state could actually be collected using WriterT, but
  -- WriterT implementations prior to transformers-0.5.6.0 (which added
  -- Control.Monad.Trans.Writer.CPS) are leaky, and we don’t have that yet.
  = CacheRWT (StateT (RebuildableSchemaCache, CacheInvalidations) m a)
  deriving
    ( Functor, Applicative, Monad, MonadIO, MonadUnique, MonadReader r, MonadError e, MonadTx
    , UserInfoM, HasHttpManagerM, HasSQLGenCtx, HasSystemDefined, MonadMetadataStorage
    , MonadMetadataStorageQueryAPI, HasRemoteSchemaPermsCtx, Tracing.MonadTrace)

deriving instance (MonadBase IO m) => MonadBase IO (CacheRWT m)
deriving instance (MonadBaseControl IO m) => MonadBaseControl IO (CacheRWT m)

runCacheRWT
  :: Functor m
  => RebuildableSchemaCache -> CacheRWT m a -> m (a, RebuildableSchemaCache, CacheInvalidations)
runCacheRWT cache (CacheRWT m) =
  runStateT m (cache, mempty) <&> \(v, (newCache, invalidations)) -> (v, newCache, invalidations)

instance MonadTrans CacheRWT where
  lift = CacheRWT . lift

instance (Monad m) => CacheRM (CacheRWT m) where
  askSchemaCache = CacheRWT $ gets (lastBuiltSchemaCache . (^. _1))

instance (MonadIO m, MonadError QErr m, HasHttpManagerM m, HasSQLGenCtx m
         , HasRemoteSchemaPermsCtx m, MonadResolveSource m) => CacheRWM (CacheRWT m) where
  buildSchemaCacheWithOptions buildReason invalidations metadata = CacheRWT do
    (RebuildableSchemaCache _ invalidationKeys rule, oldInvalidations) <- get
    let newInvalidationKeys = invalidateKeys invalidations invalidationKeys
    result <- lift $ runCacheBuildM $ flip runReaderT buildReason $
              Inc.build rule (metadata, newInvalidationKeys)
    let schemaCache = Inc.result result
        prunedInvalidationKeys = pruneInvalidationKeys schemaCache newInvalidationKeys
        !newCache = RebuildableSchemaCache schemaCache prunedInvalidationKeys (Inc.rebuildRule result)
        !newInvalidations = oldInvalidations <> invalidations
    put (newCache, newInvalidations)
    where
      -- Prunes invalidation keys that no longer exist in the schema to avoid leaking memory by
      -- hanging onto unnecessary keys.
      pruneInvalidationKeys schemaCache = over ikRemoteSchemas $ M.filterWithKey \name _ ->
        -- see Note [Keep invalidation keys for inconsistent objects]
        name `elem` getAllRemoteSchemas schemaCache

buildSchemaCacheRule
  -- Note: by supplying BuildReason via MonadReader, it does not participate in caching, which is
  -- what we want!
  :: ( HasVersion, ArrowChoice arr, Inc.ArrowDistribute arr, Inc.ArrowCache m arr
     , MonadIO m, MonadUnique m, MonadBaseControl IO m, MonadError QErr m
     , MonadReader BuildReason m, HasHttpManagerM m, HasSQLGenCtx m , HasRemoteSchemaPermsCtx m, MonadResolveSource m)
  => Env.Environment
  -> (Metadata, InvalidationKeys) `arr` SchemaCache
buildSchemaCacheRule env = proc (metadata, invalidationKeys) -> do
  invalidationKeysDep <- Inc.newDependency -< invalidationKeys

  -- Step 1: Process metadata and collect dependency information.
  (outputs, collectedInfo) <-
    runWriterA buildAndCollectInfo -< (metadata, invalidationKeysDep)
  let (inconsistentObjects, unresolvedDependencies) = partitionCollectedInfo collectedInfo

  -- Step 2: Resolve dependency information and drop dangling dependents.
  (resolvedOutputs, dependencyInconsistentObjects, resolvedDependencies) <-
    resolveDependencies -< (outputs, unresolvedDependencies)

  -- Step 3: Build the GraphQL schema.
  (gqlContext, gqlSchemaInconsistentObjects) <- runWriterA buildGQLContext -<
    ( QueryHasura
    , _boSources resolvedOutputs
    , _boRemoteSchemas resolvedOutputs
    , _boActions resolvedOutputs
    , _actNonObjects $ _boCustomTypes resolvedOutputs
    )

  -- Step 4: Build the relay GraphQL schema
  (relayContext, relaySchemaInconsistentObjects) <- runWriterA buildGQLContext -<
    ( QueryRelay
    , _boSources resolvedOutputs
    , _boRemoteSchemas resolvedOutputs
    , _boActions resolvedOutputs
    , _actNonObjects $ _boCustomTypes resolvedOutputs
    )

  returnA -< SchemaCache
    { scPostgres = _boSources resolvedOutputs
    , scActions = _boActions resolvedOutputs
    -- TODO this is not the right value: we should track what part of the schema
    -- we can stitch without consistencies, I think.
    , scRemoteSchemas = fmap fst (_boRemoteSchemas resolvedOutputs) -- remoteSchemaMap
    , scAllowlist = _boAllowlist resolvedOutputs
    -- , scCustomTypes = _boCustomTypes resolvedOutputs
    , scGQLContext = fst gqlContext
    , scUnauthenticatedGQLContext = snd gqlContext
    , scRelayContext = fst relayContext
    , scUnauthenticatedRelayContext = snd relayContext
    -- , scGCtxMap = gqlSchema
    -- , scDefaultRemoteGCtx = remoteGQLSchema
    , scDepMap = resolvedDependencies
    , scCronTriggers = _boCronTriggers resolvedOutputs
    , scInconsistentObjs =
           inconsistentObjects
        <> dependencyInconsistentObjects
        <> toList gqlSchemaInconsistentObjects
        <> toList relaySchemaInconsistentObjects
    }
  where
    resolveSourceIfNeeded
      :: ( ArrowChoice arr, Inc.ArrowCache m arr
         , ArrowWriter (Seq CollectedInfo) arr
         , MonadIO m, MonadBaseControl IO m
         , MonadResolveSource m
         )
      => ( Inc.Dependency (HashMap SourceName Inc.InvalidationKey)
         , SourceMetadata
         ) `arr` Maybe ResolvedPGSource
    resolveSourceIfNeeded = Inc.cache proc (invalidationKeys, sourceMetadata) -> do
      let sourceName = _smName sourceMetadata
          metadataObj = MetadataObject (MOSource sourceName) $ toJSON sourceName
      Inc.dependOn -< Inc.selectKeyD sourceName invalidationKeys
      (| withRecordInconsistency (
           liftEitherA <<< bindA -< resolveSource sourceName $ _smConfiguration sourceMetadata)
       |) metadataObj

    buildSource
      :: ( ArrowChoice arr, Inc.ArrowDistribute arr, Inc.ArrowCache m arr
         , ArrowWriter (Seq CollectedInfo) arr, MonadBaseControl IO m
         , HasSQLGenCtx m, MonadIO m, MonadError QErr m, MonadReader BuildReason m)
      => ( SourceMetadata
         , SourceConfig 'Postgres
         , DBTablesMetadata 'Postgres
         , PostgresFunctionsMetadata
         , RemoteSchemaMap
         , Inc.Dependency InvalidationKeys
         ) `arr` SourceInfo 'Postgres
    buildSource = proc (sourceMetadata, sourceConfig, pgTables, pgFunctions, remoteSchemaMap, invalidationKeys) -> do
      let SourceMetadata source tables functions _ = sourceMetadata
          (tableInputs, nonColumnInputs, permissions) = unzip3 $ map mkTableInputs $ OMap.elems tables
          eventTriggers = map (_tmTable &&& (OMap.elems . _tmEventTriggers)) (OMap.elems tables)
          -- HashMap k a -> HashMap k b -> HashMap k (a, b)
          alignTableMap = M.intersectionWith (,)
          metadataInvalidationKey = Inc.selectD #_ikMetadata invalidationKeys

      -- tables
      tableRawInfos <- buildTableCache -< ( source, sourceConfig, pgTables
                                          , tableInputs, metadataInvalidationKey
                                          )

      -- relationships and computed fields
      let nonColumnsByTable = mapFromL _nctiTable nonColumnInputs
      tableCoreInfos <-
        (| Inc.keyed (\_ (tableRawInfo, nonColumnInput) -> do
             let columns = _tciFieldInfoMap tableRawInfo
             allFields <- addNonColumnFields -< (source, tableRawInfos, columns, remoteSchemaMap, pgFunctions, nonColumnInput)
             returnA -< (tableRawInfo {_tciFieldInfoMap = allFields}))
         |) (tableRawInfos `alignTableMap` nonColumnsByTable)

      tableCoreInfosDep <- Inc.newDependency -< tableCoreInfos
      -- permissions and event triggers
      tableCache <-
        (| Inc.keyed (\_ ((tableCoreInfo, permissionInputs), (_, eventTriggerConfs)) -> do
             let tableFields = _tciFieldInfoMap tableCoreInfo
             permissionInfos <- buildTablePermissions -< (source, tableCoreInfosDep, tableFields, permissionInputs)
             eventTriggerInfos <- buildTableEventTriggers -< (source, sourceConfig, tableCoreInfo, eventTriggerConfs, metadataInvalidationKey)
             returnA -< TableInfo tableCoreInfo permissionInfos eventTriggerInfos
            )
         |) (tableCoreInfos `alignTableMap` mapFromL _tpiTable permissions `alignTableMap` mapFromL fst eventTriggers)

      -- sql functions
      functionCache <- (mapFromL _fmFunction (OMap.elems functions) >- returnA)
        >-> (| Inc.keyed (\_ (FunctionMetadata qf config) -> do
                 let systemDefined = SystemDefined False
                     definition = toJSON $ TrackFunction qf
                     metadataObject = MetadataObject (MOSourceObjId source $ SMOFunction qf) definition
                     schemaObject = SOSourceObj source $ SOIFunction qf
                     addFunctionContext e = "in function " <> qf <<> ": " <> e
                 (| withRecordInconsistency (
                    (| modifyErrA (do
                         let funcDefs = fromMaybe [] $ M.lookup qf pgFunctions
                         rawfi <- bindErrorA -< handleMultipleFunctions qf funcDefs
                         (fi, dep) <- bindErrorA -< mkFunctionInfo source qf systemDefined config rawfi
                         recordDependencies -< (metadataObject, schemaObject, [dep])
                         returnA -< fi)
                    |) addFunctionContext)
                  |) metadataObject) |)
        >-> (\infos -> M.catMaybes infos >- returnA)

      returnA -< SourceInfo source tableCache functionCache sourceConfig

    buildAndCollectInfo
      :: ( ArrowChoice arr, Inc.ArrowDistribute arr, Inc.ArrowCache m arr
         , ArrowWriter (Seq CollectedInfo) arr, MonadIO m, MonadUnique m, MonadError QErr m
         , MonadReader BuildReason m, MonadBaseControl IO m
         , HasHttpManagerM m, HasSQLGenCtx m, MonadResolveSource m)
      => (Metadata, Inc.Dependency InvalidationKeys) `arr` BuildOutputs
    buildAndCollectInfo = proc (metadata, invalidationKeys) -> do
      let Metadata sources remoteSchemas collections allowlists
            customTypes actions cronTriggers = metadata
          remoteSchemaPermissions =
            let remoteSchemaPermsList = OMap.toList $ _rsmPermissions <$> remoteSchemas
            in concat $ flip map remoteSchemaPermsList $
                 (\(remoteSchemaName, remoteSchemaPerms) ->
                    flip map remoteSchemaPerms $ \(RemoteSchemaPermissionMetadata role defn comment) ->
                     AddRemoteSchemaPermissions remoteSchemaName role defn comment
                 )

      -- remote schemas
      let remoteSchemaInvalidationKeys = Inc.selectD #_ikRemoteSchemas invalidationKeys
      remoteSchemaMap <- buildRemoteSchemas -< (remoteSchemaInvalidationKeys, (OMap.elems remoteSchemas))

      -- remote schema permissions
      remoteSchemaCache <- (remoteSchemaMap >- returnA)
        >-> (\info -> (info, M.groupOn _arspRemoteSchema remoteSchemaPermissions)
                     >- alignExtraRemoteSchemaInfo mkRemoteSchemaPermissionMetadataObject)
        >-> (| Inc.keyed (\_ ((remoteSchemaCtx, metadataObj), remoteSchemaPerms) -> do
                   permissionInfo <-
                     buildRemoteSchemaPermissions -< (remoteSchemaCtx, remoteSchemaPerms)
                   returnA -< (remoteSchemaCtx
                               { _rscPermissions = permissionInfo
                               }
                              , metadataObj)
                   )
             |)


      sourcesOutput <-
        (| Inc.keyed (\_ sourceMetadata -> do
             let sourceInvalidationsKeys = Inc.selectD #_ikSources invalidationKeys
             maybeResolvedSource <- resolveSourceIfNeeded -< (sourceInvalidationsKeys, sourceMetadata)
             case maybeResolvedSource of
               Nothing -> returnA -< Nothing
               Just (ResolvedPGSource pgSourceConfig tablesMeta functionsMeta pgScalars) -> do
                 so <- buildSource -< ( sourceMetadata, pgSourceConfig, tablesMeta, functionsMeta
                                      , M.map fst remoteSchemaMap, invalidationKeys
                                      )
                 returnA -< Just (so, pgScalars))
         |) (M.fromList $ OMap.toList sources)
        >-> (\infos -> M.catMaybes infos >- returnA)

      -- allow list
      let allowList = allowlists
            & HSIns.toList
            & map _crCollection
            & map (\cn -> maybe [] (_cdQueries . _ccDefinition) $ OMap.lookup cn collections)
            & concat
            & map (queryWithoutTypeNames . getGQLQuery . _lqQuery)
            & HS.fromList

      -- custom types
      let pgScalars = mconcat $ map snd $ M.elems sourcesOutput
          sourcesCache = M.map fst sourcesOutput
      maybeResolvedCustomTypes <-
        (| withRecordInconsistency
             (bindErrorA -< resolveCustomTypes sourcesCache customTypes pgScalars)
         |) (MetadataObject MOCustomTypes $ toJSON customTypes)

      -- -- actions
      let actionList = OMap.elems actions
      (actionCache, annotatedCustomTypes) <- case maybeResolvedCustomTypes of
        Just resolvedCustomTypes -> do
          actionCache' <- buildActions -< ((resolvedCustomTypes, pgScalars), actionList)
          returnA -< (actionCache', resolvedCustomTypes)

        -- If the custom types themselves are inconsistent, we can’t really do
        -- anything with actions, so just mark them all inconsistent.
        Nothing -> do
          recordInconsistencies -< ( map mkActionMetadataObject actionList
                                   , "custom types are inconsistent" )
          returnA -< (M.empty, emptyAnnotatedCustomTypes)

      cronTriggersMap <- buildCronTriggers -< ((), OMap.elems cronTriggers)

      returnA -< BuildOutputs
        { _boSources = M.map fst sourcesOutput
        , _boActions = actionCache
        , _boRemoteSchemas = remoteSchemaCache
        , _boAllowlist = allowList
        , _boCustomTypes = annotatedCustomTypes
        , _boCronTriggers = cronTriggersMap
        }

    mkEventTriggerMetadataObject (_, source, _, table, eventTriggerConf) =
      let objectId = MOSourceObjId source $
                     SMOTableObj table $ MTOTrigger $ etcName eventTriggerConf
          definition = object ["table" .= table, "configuration" .= eventTriggerConf]
      in MetadataObject objectId definition

    mkCronTriggerMetadataObject catalogCronTrigger =
      let definition = toJSON catalogCronTrigger
      in MetadataObject (MOCronTrigger (ctName catalogCronTrigger))
                        definition

    mkActionMetadataObject (ActionMetadata name comment defn _) =
      MetadataObject (MOAction name) (toJSON $ CreateAction name defn comment)

    mkRemoteSchemaMetadataObject remoteSchema =
      MetadataObject (MORemoteSchema (_rsmName remoteSchema)) (toJSON remoteSchema)

    alignExtraRemoteSchemaInfo
      :: forall a b arr
       . (ArrowChoice arr, Inc.ArrowDistribute arr, ArrowWriter (Seq CollectedInfo) arr)
      => (b -> MetadataObject)
      -> ( M.HashMap RemoteSchemaName a
         , M.HashMap RemoteSchemaName [b]
         ) `arr` M.HashMap RemoteSchemaName (a, [b])
    alignExtraRemoteSchemaInfo mkMetadataObject = proc (baseInfo, extraInfo) -> do
      combinedInfo <-
        (| Inc.keyed (\remoteSchemaName infos -> combine -< (remoteSchemaName, infos))
        |) (align baseInfo extraInfo)
      returnA -< M.catMaybes combinedInfo
      where
        combine :: (RemoteSchemaName, These a [b]) `arr` Maybe (a, [b])
        combine = proc (remoteSchemaName, infos) -> case infos of
          This  base        -> returnA -< Just (base, [])
          These base extras -> returnA -< Just (base, extras)
          That       extras -> do
            let errorMessage = "remote schema  " <> unRemoteSchemaName remoteSchemaName <<> " does not exist"
            recordInconsistencies -< (map mkMetadataObject extras, errorMessage)
            returnA -< Nothing

    buildRemoteSchemaPermissions
      :: ( ArrowChoice arr, Inc.ArrowDistribute arr, ArrowWriter (Seq CollectedInfo) arr
         , Inc.ArrowCache m arr, MonadError QErr m)
      => (RemoteSchemaCtx, [AddRemoteSchemaPermissions]) `arr` (M.HashMap RoleName IntrospectionResult)
    buildRemoteSchemaPermissions = buildInfoMap _arspRole mkRemoteSchemaPermissionMetadataObject buildRemoteSchemaPermission
      where
        buildRemoteSchemaPermission = proc (remoteSchemaCtx, remoteSchemaPerm) -> do
          let AddRemoteSchemaPermissions rsName roleName defn _ = remoteSchemaPerm
              metadataObject = mkRemoteSchemaPermissionMetadataObject remoteSchemaPerm
              schemaObject = SORemoteSchemaPermission rsName roleName
              providedSchemaDoc = _rspdSchema defn
              addPermContext err = "in remote schema permission for role " <> roleName <<> ": " <> err
          (| withRecordInconsistency (
             (| modifyErrA (do
                 bindErrorA -< when (roleName == adminRoleName) $
                   throw400 ConstraintViolation $ "cannot define permission for admin role"
                 (resolvedSchemaIntrospection, dependencies) <-
                    bindErrorA -< resolveRoleBasedRemoteSchema providedSchemaDoc remoteSchemaCtx
                 recordDependencies -< (metadataObject, schemaObject, dependencies)
                 returnA -< resolvedSchemaIntrospection)
             |) addPermContext)
           |) metadataObject

    buildTableEventTriggers
      :: ( ArrowChoice arr, Inc.ArrowDistribute arr, ArrowWriter (Seq CollectedInfo) arr
         , Inc.ArrowCache m arr, MonadIO m, MonadError QErr m, MonadBaseControl IO m
         , MonadReader BuildReason m, HasSQLGenCtx m)
      => ( SourceName, SourceConfig 'Postgres, TableCoreInfo 'Postgres
         , [EventTriggerConf], Inc.Dependency Inc.InvalidationKey
         ) `arr` EventTriggerInfoMap
    buildTableEventTriggers = proc (source, sourceConfig, tableInfo, eventTriggerConfs, metadataInvalidationKey) ->
      buildInfoMap (etcName . (^. _5)) mkEventTriggerMetadataObject buildEventTrigger
        -< (tableInfo, map (metadataInvalidationKey, source, sourceConfig, _tciName tableInfo,) eventTriggerConfs)
      where
        buildEventTrigger = proc (tableInfo, (metadataInvalidationKey, source, sourceConfig, table, eventTriggerConf)) -> do
          let triggerName = etcName eventTriggerConf
              metadataObject = mkEventTriggerMetadataObject (metadataInvalidationKey, source, sourceConfig, table, eventTriggerConf)
              schemaObjectId = SOSourceObj source $
                               SOITableObj table $ TOTrigger triggerName
              addTriggerContext e = "in event trigger " <> triggerName <<> ": " <> e
          (| withRecordInconsistency (
             (| modifyErrA (do
                  (info, dependencies) <- bindErrorA -< mkEventTriggerInfo env source table eventTriggerConf
                  let tableColumns = M.mapMaybe (^? _FIColumn) (_tciFieldInfoMap tableInfo)
                  recreateTriggerIfNeeded -< (metadataInvalidationKey, table, M.elems tableColumns, triggerName, etcDefinition eventTriggerConf, sourceConfig)
                  recordDependencies -< (metadataObject, schemaObjectId, dependencies)
                  returnA -< info)
             |) (addTableContext table . addTriggerContext))
           |) metadataObject

        recreateTriggerIfNeeded = Inc.cache proc (metadataInvalidationKey, tableName, tableColumns
                                                 , triggerName, triggerDefinition, sourceConfig) -> do
          -- We want to make sure we re-create event triggers in postgres database on
          -- `reload_metadata` metadata query request
          Inc.dependOn -< metadataInvalidationKey
          bindA -< do
            buildReason <- ask
            when (buildReason == CatalogUpdate) $
              liftEitherM $ runPgSourceWriteTx sourceConfig $
                createPostgresTableEventTrigger tableName tableColumns triggerName triggerDefinition

    buildCronTriggers
      :: ( ArrowChoice arr
         , Inc.ArrowDistribute arr
         , ArrowWriter (Seq CollectedInfo) arr
         , Inc.ArrowCache m arr
         , MonadError QErr m)
      => ((),[CronTriggerMetadata])
         `arr` HashMap TriggerName CronTriggerInfo
    buildCronTriggers = buildInfoMap ctName mkCronTriggerMetadataObject buildCronTrigger
      where
        buildCronTrigger = proc (_,cronTrigger) -> do
          let triggerName = triggerNameToTxt $ ctName cronTrigger
              addCronTriggerContext e = "in cron trigger " <> triggerName <> ": " <> e
          (| withRecordInconsistency (
            (| modifyErrA (bindErrorA -< resolveCronTrigger env cronTrigger)
             |) addCronTriggerContext)
           |) (mkCronTriggerMetadataObject cronTrigger)

    buildActions
      :: ( ArrowChoice arr, Inc.ArrowDistribute arr, Inc.ArrowCache m arr
         , ArrowWriter (Seq CollectedInfo) arr)
      => ( (AnnotatedCustomTypes 'Postgres, HashSet PGScalarType)
         , [ActionMetadata]
         ) `arr` HashMap ActionName (ActionInfo 'Postgres)
    buildActions = buildInfoMap _amName mkActionMetadataObject buildAction
      where
        buildAction = proc ((resolvedCustomTypes, pgScalars), action) -> do
          let ActionMetadata name comment def actionPermissions = action
              addActionContext e = "in action " <> name <<> "; " <> e
          (| withRecordInconsistency (
             (| modifyErrA (do
                  (resolvedDef, outObject) <- liftEitherA <<< bindA -<
                    runExceptT $ resolveAction env resolvedCustomTypes def pgScalars
                  let permissionInfos = map (ActionPermissionInfo . _apmRole) actionPermissions
                      permissionMap = mapFromL _apiRole permissionInfos
                  returnA -< ActionInfo name outObject resolvedDef permissionMap comment)
              |) addActionContext)
           |) (mkActionMetadataObject action)

    buildRemoteSchemas
      :: ( ArrowChoice arr, Inc.ArrowDistribute arr, ArrowWriter (Seq CollectedInfo) arr
         , Inc.ArrowCache m arr , MonadIO m, MonadUnique m, HasHttpManagerM m )
      => ( Inc.Dependency (HashMap RemoteSchemaName Inc.InvalidationKey)
         , [RemoteSchemaMetadata]
         ) `arr` HashMap RemoteSchemaName (RemoteSchemaCtx, MetadataObject)
    buildRemoteSchemas =
      buildInfoMapPreservingMetadata _rsmName mkRemoteSchemaMetadataObject buildRemoteSchema
      where
        -- We want to cache this call because it fetches the remote schema over HTTP, and we don’t
        -- want to re-run that if the remote schema definition hasn’t changed.
        buildRemoteSchema = Inc.cache proc (invalidationKeys, remoteSchema@(RemoteSchemaMetadata name defn comment _)) -> do
          let addRemoteSchemaQuery = AddRemoteSchemaQuery name defn comment
          Inc.dependOn -< Inc.selectKeyD name invalidationKeys
          (| withRecordInconsistency (liftEitherA <<< bindA -<
               runExceptT $ addRemoteSchemaP2Setup env addRemoteSchemaQuery)
           |) (mkRemoteSchemaMetadataObject remoteSchema)

-- | @'withMetadataCheck' cascade action@ runs @action@ and checks if the schema changed as a
-- result. If it did, it checks to ensure the changes do not violate any integrity constraints, and
-- if not, incorporates them into the schema cache.
withMetadataCheck
  :: (MonadIO m, MonadBaseControl IO m, MonadError QErr m, CacheRWM m, HasSQLGenCtx m, MetadataM m)
  => SourceName -> Bool -> Q.TxAccess -> LazyTxT QErr m a -> m a
withMetadataCheck source cascade txAccess action = do
  SourceInfo _ preActionTables preActionFunctions sourceConfig <- askPGSourceCache source

  (actionResult, metadataUpdater) <-
    liftEitherM $ runExceptT $ runLazyTx (_pscExecCtx sourceConfig) txAccess $ do
      -- Drop event triggers so no interference is caused to the sql query
      forM_ (M.elems preActionTables) $ \tableInfo -> do
        let eventTriggers = _tiEventTriggerInfoMap tableInfo
        forM_ (M.keys eventTriggers) (liftTx . delTriggerQ)

      -- Get the metadata before the sql query, everything, need to filter this
      (preActionTableMeta, preActionFunctionMeta) <- fetchMeta preActionTables preActionFunctions

      -- Run the action
      actionResult <- action
      -- Get the metadata after the sql query
      (postActionTableMeta, postActionFunctionMeta) <- fetchMeta preActionTables preActionFunctions

      let preActionTableMeta' = filter (flip M.member preActionTables . tmTable) preActionTableMeta
          schemaDiff = getSchemaDiff preActionTableMeta' postActionTableMeta
          FunctionDiff droppedFuncs alteredFuncs = getFuncDiff preActionFunctionMeta postActionFunctionMeta
          overloadedFuncs = getOverloadedFuncs (M.keys preActionFunctions) postActionFunctionMeta

      -- Do not allow overloading functions
      unless (null overloadedFuncs) $
        throw400 NotSupported $ "the following tracked function(s) cannot be overloaded: "
        <> commaSeparated overloadedFuncs

      indirectDeps <- getSchemaChangeDeps source schemaDiff

      -- Report back with an error if cascade is not set
      when (indirectDeps /= [] && not cascade) $ reportDepsExt indirectDeps []

      metadataUpdater <- execWriterT $ do
        -- Purge all the indirect dependents from state
        mapM_ (purgeDependentObject >=> tell) indirectDeps

        -- Purge all dropped functions
        let purgedFuncs = flip mapMaybe indirectDeps $ \case
              SOSourceObj _ (SOIFunction qf) -> Just qf
              _                              -> Nothing

        forM_ (droppedFuncs \\ purgedFuncs) $ tell . dropFunctionInMetadata source

        -- Process altered functions
        forM_ alteredFuncs $ \(qf, newTy) -> do
          when (newTy == FTVOLATILE) $
            throw400 NotSupported $
            "type of function " <> qf <<> " is altered to \"VOLATILE\" which is not supported now"

        -- update the metadata with the changes
        processSchemaChanges preActionTables schemaDiff

      pure (actionResult, metadataUpdater)

  -- Build schema cache with updated metadata
  withNewInconsistentObjsCheck $
    buildSchemaCacheWithInvalidations mempty{ciSources = HS.singleton source} metadataUpdater

  postActionSchemaCache <- askSchemaCache

  -- Recreate event triggers in hdb_catalog
  let postActionTables = maybe mempty _pcTables $ M.lookup source $ scPostgres postActionSchemaCache
  liftEitherM $ runPgSourceWriteTx sourceConfig $
    forM_ (M.elems postActionTables) $ \(TableInfo coreInfo _ eventTriggers) -> do
      let table = _tciName coreInfo
          columns = getCols $ _tciFieldInfoMap coreInfo
      forM_ (M.toList eventTriggers) $ \(triggerName, eti) -> do
        let opsDefinition = etiOpsDef eti
        mkAllTriggersQ triggerName table columns opsDefinition

  pure actionResult
  where
    processSchemaChanges
      :: ( MonadError QErr m
         , CacheRM m
         , MonadWriter MetadataModifier m
         )
      => TableCache 'Postgres -> SchemaDiff 'Postgres -> m ()
    processSchemaChanges preActionTables schemaDiff = do
      -- Purge the dropped tables
      forM_ droppedTables $
        \tn -> tell $ MetadataModifier $ metaSources.ix source.smTables %~ OMap.delete tn

      for_ alteredTables $ \(oldQtn, tableDiff) -> do
        ti <- onNothing
          (M.lookup oldQtn preActionTables)
          (throw500 $ "old table metadata not found in cache : " <>> oldQtn)
        processTableChanges source (_tiCoreInfo ti) tableDiff
      where
        SchemaDiff droppedTables alteredTables = schemaDiff

{- Note [Keep invalidation keys for inconsistent objects]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
After building the schema cache, we prune InvalidationKeys for objects
that no longer exist in the schema to avoid leaking memory for objects
that have been dropped. However, note that we *don’t* want to drop
keys for objects that are simply inconsistent!

Why? The object is still in the metadata, so next time we reload it,
we’ll reprocess that object. We want to reuse the cache if its
definition hasn’t changed, but if we dropped the invalidation key, it
will incorrectly be reprocessed (since the invalidation key changed
from present to absent). -}