Add FK creation in migration v2 (#14685)

## Context
-
packages/twenty-server/src/engine/metadata-modules/object-metadata/utils/build-default-relation-flat-field-metadatas-for-custom-object.util.ts
Fixing targetFlatFieldMetadata not being accurate for default relation
during object creation (was not used yet)
-
packages/twenty-server/src/engine/twenty-orm/workspace-schema-manager/services/workspace-schema-foreign-key-manager.service.ts
Simplifying API + Removing unused methods and the ones that were
querying pg schema as we want to avoid those as much as possible
-
packages/twenty-server/src/engine/workspace-manager/workspace-migration-v2/workspace-migration-runner-v2/action-handlers/field/services/create-field-action-handler.service.ts
Adding FK creation when Join column is created

packages/twenty-server/src/engine/workspace-manager/workspace-migration-v2/workspace-migration-runner-v2/action-handlers/field/services/create-field-action-handler.service.ts

@@ -1,5 +1,8 @@
 import { Injectable } from '@nestjs/common';
 
+import { RelationType } from 'twenty-shared/types';
+import { isDefined } from 'twenty-shared/utils';
+
 import {
   OptimisticallyApplyActionOnAllFlatEntityMapsArgs,
   WorkspaceMigrationRunnerActionHandler,
@@ -7,9 +10,12 @@ import {
 
 import { AllFlatEntityMaps } from 'src/engine/core-modules/common/types/all-flat-entity-maps.type';
 import { FieldMetadataEntity } from 'src/engine/metadata-modules/field-metadata/field-metadata.entity';
+import { isMorphOrRelationFlatFieldMetadata } from 'src/engine/metadata-modules/flat-field-metadata/utils/is-morph-or-relation-flat-field-metadata.util';
 import { addFlatFieldMetadataInFlatObjectMetadataMapsOrThrow } from 'src/engine/metadata-modules/flat-object-metadata-maps/utils/add-flat-field-metadata-in-flat-object-metadata-maps-or-throw.util';
 import { findFlatObjectMetadataWithFlatFieldMapsInFlatObjectMetadataMapsOrThrow } from 'src/engine/metadata-modules/flat-object-metadata-maps/utils/find-flat-object-metadata-with-flat-field-maps-in-flat-object-metadata-maps-or-throw.util';
 import { WorkspaceSchemaManagerService } from 'src/engine/twenty-orm/workspace-schema-manager/workspace-schema-manager.service';
+import { computeObjectTargetTable } from 'src/engine/utils/compute-object-target-table.util';
+import { convertOnDeleteActionToOnDelete } from 'src/engine/workspace-manager/workspace-migration-runner/utils/convert-on-delete-action-to-on-delete.util';
 import { type CreateFieldAction } from 'src/engine/workspace-manager/workspace-migration-v2/workspace-migration-builder-v2/types/workspace-migration-field-action-v2';
 import { type WorkspaceMigrationActionRunnerArgs } from 'src/engine/workspace-manager/workspace-migration-v2/workspace-migration-runner-v2/types/workspace-migration-action-runner-args.type';
 import { generateColumnDefinitions } from 'src/engine/workspace-manager/workspace-migration-v2/workspace-migration-runner-v2/utils/generate-column-definitions.util';
@@ -106,5 +112,39 @@ export class CreateFieldActionHandlerService extends WorkspaceMigrationRunnerAct
       tableName,
       columnDefinitions,
     });
+
+    if (
+      isMorphOrRelationFlatFieldMetadata(flatFieldMetadata) &&
+      flatFieldMetadata.settings.relationType === RelationType.MANY_TO_ONE
+    ) {
+      const referencedTableName = computeObjectTargetTable(
+        flatFieldMetadata.flatRelationTargetObjectMetadata,
+      );
+
+      const joinColumnName = flatFieldMetadata.settings.joinColumnName;
+
+      if (!isDefined(joinColumnName)) {
+        throw new Error(
+          'Join column name is not defined in a MANY_TO_ONE relation',
+        );
+      }
+
+      await this.workspaceSchemaManagerService.foreignKeyManager.createForeignKey(
+        {
+          queryRunner,
+          schemaName,
+          foreignKey: {
+            tableName,
+            columnName: joinColumnName,
+            referencedTableName,
+            referencedColumnName: 'id',
+            onDelete:
+              convertOnDeleteActionToOnDelete(
+                flatFieldMetadata.settings.onDelete,
+              ) ?? 'CASCADE',
+          },
+        },
+      );
+    }
   }
 }