function hook_schema

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.

The tables declared by this hook will be automatically created when the module is installed, 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 https://www.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.

Related topics

Hooks

Define functions that alter the behavior of Drupal core.

Schema API

API to handle database schemas.

File

core/lib/Drupal/Core/Database/database.api.php, line 484

Hooks related to the Database system and the Schema API.

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_field_revision}.vid version identifier.',
        'type' => 'int',
        'unsigned' => TRUE,
        'not null' => TRUE,
        'default' => 0,
      ),
      'type' => array(
        'description' => 'The type of this node.',
        'type' => 'varchar',
        'length' => 32,
        'not null' => TRUE,
        'default' => '',
      ),
      'title' => array(
        'description' => 'The node title.',
        '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_field_revision',
        'columns' => array('vid' => 'vid'),
      ),
      'node_author' => array(
        'table' => 'users',
        'columns' => array('uid' => 'uid'),
      ),
    ),
    'primary key' => array('nid'),
  );
  return $schema;
}