server: fix bug when downgrading from v2 to v1 when there is atleast one cron trigger present in the metadata

https://github.com/hasura/graphql-engine-mono/pull/2101

GitOrigin-RevId: 7011f0c18cb0cef828214ec084adc39cfb3aba1c

CHANGELOG.md

@@ -4,6 +4,8 @@
 
 (Add entries below in the order of server, console, cli, docs, others)
 
+
+- server: fix v2 -> v1 downgrade bug when cron triggers exist
 - server: add index on the `event_id` column of the `hdb_cron_event_invocation_logs` table
 - server: fix GraphQL type for remote relationship field (close #7284)
 - server: support EdDSA algorithm and key type for JWT

server/src-lib/Hasura/RQL/DDL/Schema/LegacyCatalog.hs

@@ -3,6 +3,7 @@ module Hasura.RQL.DDL.Schema.LegacyCatalog
   ( saveMetadataToHdbTables
   , fetchMetadataFromHdbTables
   , recreateSystemMetadata
+  , addCronTriggerForeignKeyConstraint
   ) where
 
 import           Hasura.Prelude
@@ -529,6 +530,16 @@ fetchMetadataFromHdbTables = liftTx do
                           , RemoteRelationshipMetadata name definition
                           )
 
+addCronTriggerForeignKeyConstraint :: MonadTx m => m ()
+addCronTriggerForeignKeyConstraint =
+  liftTx $
+  Q.unitQE defaultTxErrorHandler [Q.sql|
+      ALTER TABLE hdb_catalog.hdb_cron_events ADD CONSTRAINT
+     hdb_cron_events_trigger_name_fkey FOREIGN KEY (trigger_name)
+     REFERENCES hdb_catalog.hdb_cron_triggers(name)
+     ON UPDATE CASCADE ON DELETE CASCADE;
+     |] () False
+
 -- | Drops and recreates all “system-defined” metadata, aka metadata for tables and views in the
 -- @information_schema@ and @hdb_catalog@ schemas. These tables and views are tracked to expose them
 -- to the console, which allows us to reuse the same functionality we use to implement user-defined

server/src-lib/Hasura/Server/Migrate.hs

@@ -301,5 +301,12 @@ migrations maybeDefaultSourceConfig dryRun maintenanceMode =
                 MetadataNoSources _smTables _smFunctions _metaRemoteSchemas _metaQueryCollections
                                   _metaAllowlist _metaCustomTypes _metaActions _metaCronTriggers
           _ -> throw400 NotSupported "Cannot downgrade since there are more than one source"
-        liftTx $ runHasSystemDefinedT (SystemDefined False) $ saveMetadataToHdbTables metadataV2
+        liftTx $ do
+          runHasSystemDefinedT (SystemDefined False) $ saveMetadataToHdbTables metadataV2
+          -- when the graphql-engine is migrated from v1 to v2, we drop the foreign key
+          -- constraint of the `hdb_catalog.hdb_cron_event` table because the cron triggers
+          -- in v2 are saved in the `hdb_catalog.hdb_metadata` table. So, when a downgrade
+          -- happens, we need to delay adding the foreign key constraint until the
+          -- cron triggers are added in the `hdb_catalog.hdb_cron_triggers`
+          addCronTriggerForeignKeyConstraint
         recreateSystemMetadata

server/src-rsr/migrations/43_to_42.sql

@@ -675,11 +675,16 @@ CREATE TABLE hdb_catalog.hdb_cron_triggers
   comment TEXT
 );
 
+-- The below statement is run separately and is run after the cron triggers
+-- are inserted in the hdb_catalog.hdb_cron_events table. See `from43To42`
+-- in Migrate.hs for more details.
+
+
 -- Add foreign key constraint from hdb_cron_events to hdb_cron_triggers
-ALTER TABLE hdb_catalog.hdb_cron_events ADD CONSTRAINT
-  hdb_cron_events_trigger_name_fkey FOREIGN KEY (trigger_name)
-  REFERENCES hdb_catalog.hdb_cron_triggers(name)
-  ON UPDATE CASCADE ON DELETE CASCADE;
+-- ALTER TABLE hdb_catalog.hdb_cron_events ADD CONSTRAINT
+--   hdb_cron_events_trigger_name_fkey FOREIGN KEY (trigger_name)
+--   REFERENCES hdb_catalog.hdb_cron_triggers(name)
+--   ON UPDATE CASCADE ON DELETE CASCADE;
 
 CREATE VIEW hdb_catalog.hdb_cron_events_stats AS
   SELECT ct.name,