function hook_schema

Define the current version of the database schema.

A Drupal schema definition is an array structure representing one or more tables and their related keys and indexes. A schema is defined by hook_schema() which must live in your module's .install file.

This hook is called at install and uninstall time, and in the latter case, it cannot rely on the .module file being loaded or hooks being known. If the .module file is needed, it may be loaded with drupal_load().

The tables declared by this hook will be automatically created when the module is first enabled, and removed when the module is uninstalled. This happens before hook_install() is invoked, and after hook_uninstall() is invoked, respectively.

By declaring the tables used by your module via an implementation of hook_schema(), these tables will be available on all supported database engines. You don't have to deal with the different SQL dialects for table creation and alteration of the supported database engines.

See the Schema API Handbook at http://drupal.org/node/146843 for details on schema definition structures. Note that foreign key definitions are for documentation purposes only; foreign keys are not created in the database, nor are they enforced by Drupal.

Return value

array A schema definition structure array. For each element of the array, the key is a table name and the value is a table structure definition.

See also

hook_schema_alter()

Related topics

File

drupal/modules/system/system.api.php, line 3221

Hooks provided by Drupal core and the System module.

Code

function hook_schema() {
  $schema['node'] = array(
    // Example (partial) specification for table "node".
    'description' => 'The base table for nodes.',
    'fields' => array(
      'nid' => array(
        'description' => 'The primary identifier for a node.',
        'type' => 'serial',
        'unsigned' => TRUE,
        'not null' => TRUE,
      ),
      'vid' => array(
        'description' => 'The current {node_revision}.vid version identifier.',
        'type' => 'int',
        'unsigned' => TRUE,
        'not null' => TRUE,
        'default' => 0,
      ),
      'type' => array(
        'description' => 'The {node_type} of this node.',
        'type' => 'varchar',
        'length' => 32,
        'not null' => TRUE,
        'default' => '',
      ),
      'title' => array(
        'description' => 'The title of this node, always treated as non-markup plain text.',
        'type' => 'varchar',
        'length' => 255,
        'not null' => TRUE,
        'default' => '',
      ),
    ),
    'indexes' => array(
      'node_changed' => array(
        'changed',
      ),
      'node_created' => array(
        'created',
      ),
    ),
    'unique keys' => array(
      'nid_vid' => array(
        'nid',
        'vid',
      ),
      'vid' => array(
        'vid',
      ),
    ),
    // For documentation purposes only; foreign keys are not created in the
    // database.
    'foreign keys' => array(
      'node_revision' => array(
        'table' => 'node_revision',
        'columns' => array(
          'vid' => 'vid',
        ),
      ),
      'node_author' => array(
        'table' => 'users',
        'columns' => array(
          'uid' => 'uid',
        ),
      ),
    ),
    'primary key' => array(
      'nid',
    ),
  );
  return $schema;
}