Perform change_foreign_key in two steps required for some databases

Author: avoutic

docs/database-migrations.md

@@ -483,7 +483,7 @@ return [
 
 ## Modify Foreign Key
 
-Modifies an existing foreign key constraint (e.g. change referenced table, `ON DELETE`/`ON UPDATE` behaviour). Implemented as drop then add with new options.
+Modifies an existing foreign key constraint (e.g. change referenced table, `ON DELETE`/`ON UPDATE` behaviour). Executed as two separate statements: first DROP FOREIGN KEY, then ADD CONSTRAINT (databases do not allow drop and add in a single ALTER TABLE).
 
 ### Fields
 - `type` (required): Must be "modify_foreign_key"

src/Migration/Action/ActionHandler.php

@@ -25,6 +25,8 @@ public function getType(): string;
 
     /**
      * @param array<string, mixed> $action
+     *
+     * @return array<MigrationStep>|MigrationStep
      */
-    public function buildStep(array $action): MigrationStep;
+    public function buildStep(array $action): array|MigrationStep;
 }

src/Migration/Action/ModifyForeignKeyActionHandler.php

@@ -21,7 +21,10 @@ public function getType(): string
         return 'modify_foreign_key';
     }
 
-    public function buildStep(array $action): MigrationStep
+    /**
+     * @return array<MigrationStep>
+     */
+    public function buildStep(array $action): array
     {
         $tableName = $this->requireTableName($action);
 
@@ -49,8 +52,15 @@ public function buildStep(array $action): MigrationStep
         $onDelete = isset($action['on_delete']) ? 'ON DELETE '.$action['on_delete'] : '';
         $onUpdate = isset($action['on_update']) ? 'ON UPDATE '.$action['on_update'] : '';
 
-        $addPart = sprintf(
-            'ADD CONSTRAINT `%s` FOREIGN KEY (`%s`) REFERENCES `%s` (`%s`) %s %s',
+        $dropQuery = sprintf(
+            "ALTER TABLE `%s`\n    DROP FOREIGN KEY `%s`",
+            $tableName,
+            $constraintName
+        );
+
+        $addQuery = sprintf(
+            "ALTER TABLE `%s`\n    ADD CONSTRAINT `%s` FOREIGN KEY (`%s`) REFERENCES `%s` (`%s`) %s %s",
+            $tableName,
             $constraintName,
             $action['column'],
             $action['foreign_table'],
@@ -59,13 +69,9 @@ public function buildStep(array $action): MigrationStep
             $onUpdate
         );
 
-        $query = sprintf(
-            "ALTER TABLE `%s`\n    DROP FOREIGN KEY `%s`,\n    %s",
-            $tableName,
-            $constraintName,
-            trim($addPart)
-        );
-
-        return new QueryStep($query, []);
+        return [
+            new QueryStep($dropQuery, []),
+            new QueryStep(trim($addQuery), []),
+        ];
     }
 }

src/Migration/DatabaseManager.php

@@ -89,7 +89,8 @@ public function execute(array $data, bool $dryRun = false): void
             }
 
             $handler = $this->getHandler($action['type']);
-            $steps[] = $handler->buildStep($action);
+            $stepOrSteps = $handler->buildStep($action);
+            $steps = array_merge($steps, is_array($stepOrSteps) ? $stepOrSteps : [$stepOrSteps]);
         }
 
         if ($dryRun)

tests/Unit/Migration/Action/ModifyForeignKeyActionHandlerTest.php

@@ -20,7 +20,7 @@ public function testGetType()
         verify($handler->getType())->equals('modify_foreign_key');
     }
 
-    public function testBuildStepWithValidAction()
+    public function testBuildStepWithValidActionReturnsTwoSteps()
     {
         $handler = new ModifyForeignKeyActionHandler();
         $action = [
@@ -33,16 +33,21 @@ public function testBuildStepWithValidAction()
             'on_update' => 'CASCADE',
         ];
 
-        $step = $handler->buildStep($action);
-        verify($step)->instanceOf(QueryStep::class);
-        verify($step->getQuery())->stringContainsString('ALTER TABLE `orders`');
-        verify($step->getQuery())->stringContainsString('DROP FOREIGN KEY `orders_fk_user_id`');
-        verify($step->getQuery())->stringContainsString('ADD CONSTRAINT `orders_fk_user_id`');
-        verify($step->getQuery())->stringContainsString('FOREIGN KEY (`user_id`)');
-        verify($step->getQuery())->stringContainsString('REFERENCES `users` (`id`)');
-        verify($step->getQuery())->stringContainsString('ON DELETE SET NULL');
-        verify($step->getQuery())->stringContainsString('ON UPDATE CASCADE');
-        verify($step->getParams())->equals([]);
+        $steps = $handler->buildStep($action);
+        verify($steps)->isArray();
+        verify($steps)->arrayCount(2);
+        verify($steps[0])->instanceOf(QueryStep::class);
+        verify($steps[1])->instanceOf(QueryStep::class);
+        verify($steps[0]->getQuery())->stringContainsString('ALTER TABLE `orders`');
+        verify($steps[0]->getQuery())->stringContainsString('DROP FOREIGN KEY `orders_fk_user_id`');
+        verify($steps[1]->getQuery())->stringContainsString('ALTER TABLE `orders`');
+        verify($steps[1]->getQuery())->stringContainsString('ADD CONSTRAINT `orders_fk_user_id`');
+        verify($steps[1]->getQuery())->stringContainsString('FOREIGN KEY (`user_id`)');
+        verify($steps[1]->getQuery())->stringContainsString('REFERENCES `users` (`id`)');
+        verify($steps[1]->getQuery())->stringContainsString('ON DELETE SET NULL');
+        verify($steps[1]->getQuery())->stringContainsString('ON UPDATE CASCADE');
+        verify($steps[0]->getParams())->equals([]);
+        verify($steps[1]->getParams())->equals([]);
     }
 
     public function testBuildStepThrowsExceptionWhenTableNameMissing()