- Patch #396578 by Damien Tournoud: added db_truncate_table() to the database layer.

includes/database/database.inc

@@ -254,6 +254,13 @@ abstract class DatabaseConnection extends PDO {
    */
   protected $deleteClass = NULL;
 
+  /**
+   * The name of the Truncate class for this connection.
+   *
+   * @var string
+   */
+  protected $truncateClass = NULL;
+
   /**
    * The name of the Insert class for this connection.
    *
@@ -762,6 +769,26 @@ public function delete($table, array $options = array()) {
     return new $class($this, $table, $options);
   }
 
+  /**
+   * Prepare and return a TRUNCATE query object.
+   *
+   * @see TruncateQuery
+   * @param $options
+   *   An array of options on the query.
+   * @return
+   *   A new DeleteQuery object.
+   */
+  public function truncate($table, array $options = array()) {
+    if (empty($this->truncateClass)) {
+      $this->truncateClass = 'TruncateQuery_' . $this->driver();
+      if (!class_exists($this->truncateClass)) {
+        $this->truncateClass = 'TruncateQuery';
+      }
+    }
+    $class = $this->truncateClass;
+    return new $class($this, $table, $options);
+  }
+
   /**
    * Returns a DatabaseSchema object for manipulating the schema of this database.
    *
@@ -1880,6 +1907,23 @@ function db_delete($table, array $options = array()) {
   return Database::getConnection($options['target'])->delete($table, $options);
 }
 
+/**
+ * Returns a new TruncateQuery object for the active database.
+ *
+ * @param $table
+ *   The table from which to delete.
+ * @param $options
+ *   An array of options to control how the query operates.
+ * @return
+ *   A new TruncateQuery object for this connection.
+ */
+function db_truncate($table, array $options = array()) {
+  if (empty($options['target']) || $options['target'] == 'slave') {
+    $options['target'] = 'default';
+  }
+  return Database::getConnection($options['target'])->truncate($table, $options);
+}
+
 /**
  * Returns a new SelectQuery object for the active database.
  *

includes/database/query.inc

@@ -829,6 +829,38 @@ public function __toString() {
   }
 }
 
+
+/**
+ * General class for an abstracted TRUNCATE operation.
+ */
+class TruncateQuery extends Query {
+
+  /**
+   * The table from which to delete.
+   *
+   * @var string
+   */
+  protected $table;
+
+  public function __construct(DatabaseConnection $connection, $table, array $options = array()) {
+    $options['return'] = Database::RETURN_AFFECTED;
+    parent::__construct($connection, $options);
+    $this->table = $table;
+  }
+
+  public function compile(DatabaseConnection $connection) {
+    return $this->condition->compile($connection);
+  }
+
+  public function execute() {
+    return $this->connection->query((string)$this, array(), $this->queryOptions);
+  }
+
+  public function __toString() {
+    return 'TRUNCATE {' . $this->connection->escapeTable($this->table) . '} ';
+  }
+}
+
 /**
  * General class for an abstracted UPDATE operation.
  */

includes/database/sqlite/query.inc

@@ -135,6 +135,18 @@ public function execute() {
   }
 }
 
+/**
+ * SQLite specific implementation of TruncateQuery.
+ *
+ * SQLite doesn't support TRUNCATE, but a DELETE query with no condition has
+ * exactly the effect (it is implemented by DROPing the table).
+ */
+class TruncateQuery_sqlite extends TruncateQuery {
+  public function __toString() {
+    return 'DELETE FROM {' . $this->connection->escapeTable($this->table) . '} ';
+  }
+}
+
 /**
  * @} End of "ingroup database".
  */

modules/simpletest/tests/database_test.test

@@ -847,19 +847,22 @@ class DatabaseUpdateLOBTestCase extends DatabaseTestCase {
 }
 
 /**
- * Delete tests.
+ * Delete/Truncate tests.
  *
  * The DELETE tests are not as extensive, as all of the interesting code for
  * DELETE queries is in the conditional which is identical to the UPDATE and
  * SELECT conditional handling.
  *
+ * The TRUNCATE tests are not extensive either, because the behavior of
+ * TRUNCATE queries is not consistent across database engines. We only test
+ * that a TRUNCATE query actually deletes all rows from the target table.
  */
-class DatabaseDeleteTestCase extends DatabaseTestCase {
+class DatabaseDeleteTruncateTestCase extends DatabaseTestCase {
 
   public static function getInfo() {
     return array(
-      'name' => t('Delete tests'),
-      'description' => t('Test the Delete query builder.'),
+      'name' => t('Delete/Truncate tests'),
+      'description' => t('Test the Delete and Truncate query builders.'),
       'group' => t('Database'),
     );
   }
@@ -876,6 +879,19 @@ class DatabaseDeleteTestCase extends DatabaseTestCase {
     $num_records_after = db_query("SELECT COUNT(*) FROM {test}")->fetchField();
     $this->assertEqual($num_records_before, $num_records_after + $num_deleted, t('Deletion adds up.'));
   }
+
+
+  /**
+   * Confirm that we can truncate a whole table successfully.
+   */
+  function testTruncate() {
+    $num_records_before = db_query("SELECT COUNT(*) FROM {test}")->fetchField();
+
+    db_truncate('test')->execute();
+
+    $num_records_after = db_query("SELECT COUNT(*) FROM {test}")->fetchField();
+    $this->assertEqual(0, $num_records_after, t('Truncate really deletes everything.'));
+  }
 }
 
 /**