function hook_schema

7.x system.api.php 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.

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

45 functions implement hook_schema()

Note: this list is generated by pattern matching, so it may include some functions that are not actually implementations of this hook.

aggregator_schema in modules/aggregator/aggregator.install
Implements hook_schema().
block_schema in modules/block/block.install
Implements hook_schema().
book_schema in modules/book/book.install
Implements hook_schema().
comment_schema in modules/comment/comment.install
Implements hook_schema().
contact_schema in modules/contact/contact.install
Implements hook_schema().

... See full list

2 invocations of hook_schema()
drupal_get_complete_schema in includes/bootstrap.inc
Gets the whole database schema.
drupal_get_schema_unprocessed in includes/common.inc
Returns the unprocessed and unaltered version of a module's schema.

File

modules/system/system.api.php, line 3130
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'),
    ),
    '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;
}