Allow AUTOINCREMENT with compound PRIMARY KEY

Author: JanJakes

tests/WP_SQLite_Driver_Tests.php

@@ -4125,11 +4125,62 @@ public function testTimestampColumnNamedTimestamp() {
 		);
 	}
 
-	public function testCompoundPrimaryKeyAndAutoincrementNotSupported(): void {
-		$this->expectException( WP_SQLite_Driver_Exception::class );
-		$this->expectExceptionMessage( 'Cannot combine AUTOINCREMENT and multiple primary keys in SQLite' );
+	public function testCompoundPrimaryKeyWithAutoincrement(): void {
 		$this->assertQuery(
-			'CREATE TABLE t1 (id1 INT AUTO_INCREMENT, id2 INT, PRIMARY KEY(id1, id2))'
+			'CREATE TABLE t1 (id INT AUTO_INCREMENT, name VARCHAR(32), PRIMARY KEY(id, name))'
+		);
+
+		// Ensure auto-increment is working.
+		$this->assertQuery( "INSERT INTO t1 (name) VALUES ('A'), ('B'), ('C')" );
+		$results = $this->assertQuery( 'SELECT * FROM t1' );
+		$this->assertEquals(
+			array(
+				(object) array(
+					'id'   => 1,
+					'name' => 'A',
+				),
+				(object) array(
+					'id'   => 2,
+					'name' => 'B',
+				),
+				(object) array(
+					'id'   => 3,
+					'name' => 'C',
+				),
+			),
+			$results
+		);
+
+		// Verify the table schema.
+		$results = $this->assertQuery( 'SHOW CREATE TABLE t1' );
+		$this->assertEquals(
+			implode(
+				"\n",
+				array(
+					'CREATE TABLE `t1` (',
+					'  `id` int NOT NULL AUTO_INCREMENT,',
+					'  `name` varchar(32) NOT NULL,',
+					'  PRIMARY KEY (`id`, `name`)',
+					') ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci',
+				)
+			),
+			$results[0]->{'Create Table'}
+		);
+
+		// Ensure an SQLite index was created for the compound key columns.
+		$result = $this->engine
+			->execute_sqlite_query( "SELECT * FROM pragma_index_list('t1')" )
+			->fetchAll( PDO::FETCH_ASSOC );
+		$this->assertCount( 1, $result );
+		$this->assertEquals(
+			array(
+				'seq'     => '0',
+				'name'    => '_wp_sqlite_t1__primary',
+				'unique'  => '1',
+				'origin'  => 'c',
+				'partial' => '0',
+			),
+			$result[0]
 		);
 	}
 

wp-includes/sqlite-ast/class-wp-pdo-mysql-on-sqlite.php

@@ -5618,13 +5618,33 @@ function ( $column ) {
 
 			if ( 'PRIMARY' === $info['INDEX_NAME'] ) {
 				if ( $has_autoincrement ) {
-					if ( $has_autoincrement ) {
-						if ( count( $constraint ) > 1 ) {
-							throw $this->new_driver_exception(
-								'Cannot combine AUTOINCREMENT and multiple primary keys in SQLite'
-							);
-						}
+					/*
+					 * In MySQL, a compound PRIMARY KEY can have an AUTOINCREMENT
+					 * column, when it is the first column in the key.
+					 *
+					 * SQLite doesn't support this, but we can emulate it as follows:
+					 *   1. Keep only the first column as a PRIMARY KEY.
+					 *      Since this is the column that also has AUTOINCREMENT,
+					 *      it reasonable to assume that its values are unique.
+					 *   2. Create a UNIQUE key for all the PRIMARY KEY columns.
+					 *      This is to preserve the index of the compound key.
+					 */
+					if ( count( $constraint ) > 1 ) {
+						$sqlite_index_name      = $this->get_sqlite_index_name( $table_name, 'primary' );
+						$create_index_queries[] = sprintf(
+							'CREATE UNIQUE INDEX %s ON %s (%s)',
+							self::RESERVED_PREFIX . $sqlite_index_name,
+							$this->quote_sqlite_identifier( $table_name ),
+							implode( ', ', $column_list )
+						);
 					}
+
+					/*
+					 * The PRIMARY KEY was already generated with AUTOINCREMENT,
+					 * as required by SQLite column constraint syntax.
+					 *
+					 * @see https://www.sqlite.org/syntax/column-constraint.html
+					 */
 					continue;
 				}
 				$rows[] = sprintf( '  PRIMARY KEY (%s)', implode( ', ', $column_list ) );