Added disableForeignKeyConstraints and enableForeignKeyConstraints me…

…thods to make migrations with FKs easier. Fixes #1964

system/Database/BaseConnection.php

@@ -1697,6 +1697,30 @@ public function getForeignKeyData(string $table)
 
 	//--------------------------------------------------------------------
 
+	/**
+	 * Disables foreign key checks temporarily.
+	 */
+	public function disableForeignKeyChecks()
+	{
+		$sql = $this->_disableForeignKeyChecks();
+
+		return $this->query($sql);
+	}
+
+	//--------------------------------------------------------------------
+
+	/**
+	 * Enables foreign key checks temporarily.
+	 */
+	public function enableForeignKeyChecks()
+	{
+		$sql = $this->_enableForeignKeyChecks();
+
+		return $this->query($sql);
+	}
+
+	//--------------------------------------------------------------------
+
 	/**
 	 * Allows the engine to be set into a mode where queries are not
 	 * actually executed, but they are still generated, timed, etc.

system/Database/Forge.php

@@ -615,11 +615,11 @@ public function dropTable(string $tableName, bool $ifExists = false, bool $casca
 			return true;
 		}
 
-		$this->db->query('PRAGMA foreign_keys = OFF');
+		$this->db->disableForeignKeyChecks();
 
 		$query = $this->db->query($query);
 
-		$this->db->query('PRAGMA foreign_keys = ON');
+		$this->db->enableForeignKeyChecks();
 
 		// Update table list cache
 		if ($query && ! empty($this->db->dataCache['table_names']))

system/Database/MySQLi/Connection.php

@@ -568,6 +568,30 @@ public function _foreignKeyData(string $table): array
 
 	//--------------------------------------------------------------------
 
+	/**
+	 * Returns platform-specific SQL to disable foreign key checks.
+	 *
+	 * @return string
+	 */
+	protected function _disableForeignKeyChecks()
+	{
+		return 'SET FOREIGN_KEY_CHECKS=0';
+	}
+
+	//--------------------------------------------------------------------
+
+	/**
+	 * Returns platform-specific SQL to enable foreign key checks.
+	 *
+	 * @return string
+	 */
+	protected function _enableForeignKeyChecks()
+	{
+		return 'SET FOREIGN_KEY_CHECKS=1';
+	}
+
+	//--------------------------------------------------------------------
+
 	/**
 	 * Returns the last error code and message.
 	 *

system/Database/Postgre/Connection.php

@@ -418,6 +418,30 @@ public function _foreignKeyData(string $table): array
 
 	//--------------------------------------------------------------------
 
+	/**
+	 * Returns platform-specific SQL to disable foreign key checks.
+	 *
+	 * @return string
+	 */
+	protected function _disableForeignKeyChecks()
+	{
+		return 'SET CONSTRAINTS ALL DEFERRED';
+	}
+
+	//--------------------------------------------------------------------
+
+	/**
+	 * Returns platform-specific SQL to enable foreign key checks.
+	 *
+	 * @return string
+	 */
+	protected function _enableForeignKeyChecks()
+	{
+		return 'SET CONSTRAINTS ALL IMMEDIATE;';
+	}
+
+	//--------------------------------------------------------------------
+
 	/**
 	 * Returns the last error code and message.
 	 *

system/Database/SQLite3/Connection.php

@@ -417,6 +417,30 @@ public function _foreignKeyData(string $table): array
 
 	//--------------------------------------------------------------------
 
+	/**
+	 * Returns platform-specific SQL to disable foreign key checks.
+	 *
+	 * @return string
+	 */
+	protected function _disableForeignKeyChecks()
+	{
+		return 'PRAGMA foreign_keys = OFF';
+	}
+
+	//--------------------------------------------------------------------
+
+	/**
+	 * Returns platform-specific SQL to enable foreign key checks.
+	 *
+	 * @return string
+	 */
+	protected function _enableForeignKeyChecks()
+	{
+		return 'PRAGMA foreign_keys = ON';
+	}
+
+	//--------------------------------------------------------------------
+
 	/**
 	 * Returns the last error code and message.
 	 *

user_guide_src/source/dbmgmt/migration.rst

@@ -94,6 +94,24 @@ The database connection and the database Forge class are both available to you t
 Alternatively, you can use a command-line call to generate a skeleton migration file. See
 below for more details.
 
+Foreign Keys
+============
+
+When your tables include Foreign Keys, migrations can often cause problems as you attempt to drop tables and columns.
+To temporarily bypass the foreign key checks while running migrations, use the ``disableForeignKeyConstraints()`` and
+``enableForeignKeyConstraints()`` methods on the database connection.
+
+::
+
+    public function up()
+    {
+        $this->db->disableForeignKeyConstraints();
+
+        // Migration rules would go here...
+
+        $this->db->enableForeignKeyConstraints();
+    }
+
 Using $currentVersion
 =====================