Schema API

API to handle database schemas.

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 usually lives in a modulename.install file.

By implementing hook_schema() and specifying the tables your module declares, you can easily create and drop these tables 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.

hook_schema() should return an array with a key for each table that the module defines.

The following keys are defined:

  • 'description': A string in non-markup plain text describing this table and its purpose. References to other tables should be enclosed in curly-brackets. For example, the node_field_revision table description field might contain "Stores per-revision title and body data for each {node}."
  • 'fields': An associative array ('fieldname' => specification) that describes the table's database columns. The specification is also an array. The following specification parameters are defined:

    • 'description': A string in non-markup plain text describing this field and its purpose. References to other tables should be enclosed in curly-brackets. For example, the node table vid field description might contain "Always holds the largest (most recent) {node_field_revision}.vid value for this nid."
    • 'type': The generic datatype: 'char', 'varchar', 'text', 'blob', 'int', 'float', 'numeric', or 'serial'. Most types just map to the according database engine specific datatypes. Use 'serial' for auto incrementing fields. This will expand to 'INT auto_increment' on MySQL.
    • 'mysql_type', 'pgsql_type', 'sqlite_type', etc.: If you need to use a record type not included in the officially supported list of types above, you can specify a type for each database backend. In this case, you can leave out the type parameter, but be advised that your schema will fail to load on backends that do not have a type specified. A possible solution can be to use the "text" type as a fallback.
    • 'serialize': A boolean indicating whether the field will be stored as a serialized string.
    • 'size': The data size: 'tiny', 'small', 'medium', 'normal', 'big'. This is a hint about the largest value the field will store and determines which of the database engine specific datatypes will be used (e.g. on MySQL, TINYINT vs. INT vs. BIGINT). 'normal', the default, selects the base type (e.g. on MySQL, INT, VARCHAR, BLOB, etc.). Not all sizes are available for all data types. See DatabaseSchema::getFieldTypeMap() for possible combinations.
    • 'not null': If true, no NULL values will be allowed in this database column. Defaults to false.
    • 'default': The field's default value. The PHP type of the value matters: '', '0', and 0 are all different. If you specify '0' as the default value for a type 'int' field it will not work because '0' is a string containing the character "zero", not an integer.
    • 'length': The maximal length of a type 'char', 'varchar' or 'text' field. Ignored for other field types.
    • 'unsigned': A boolean indicating whether a type 'int', 'float' and 'numeric' only is signed or unsigned. Defaults to FALSE. Ignored for other field types.
    • 'precision', 'scale': For type 'numeric' fields, indicates the precision (total number of significant digits) and scale (decimal digits right of the decimal point). Both values are mandatory. Ignored for other field types.
    • 'binary': A boolean indicating that MySQL should force 'char', 'varchar' or 'text' fields to use case-sensitive binary collation. This has no effect on other database types for which case sensitivity is already the default behavior.

    All parameters apart from 'type' are optional except that type 'numeric' columns must specify 'precision' and 'scale', and type 'varchar' must specify the 'length' parameter.

  • 'primary key': An array of one or more key column specifiers (see below) that form the primary key.
  • 'unique keys': An associative array of unique keys ('keyname' => specification). Each specification is an array of one or more key column specifiers (see below) that form a unique key on the table.
  • 'foreign keys': An associative array of relations ('my_relation' => specification). Each specification is an array containing the name of the referenced table ('table'), and an array of column mappings ('columns'). Column mappings are defined by key pairs ('source_column' => 'referenced_column').
  • 'indexes': An associative array of indexes ('indexname' => specification). Each specification is an array of one or more key column specifiers (see below) that form an index on the table.

A key column specifier is either a string naming a column or an array of two elements, column name and length, specifying a prefix of the named column.

As an example, here is a SUBSET of the schema definition for Drupal's 'node' table. It show four fields (nid, vid, type, and title), the primary key on field 'nid', a unique key named 'vid' on field 'vid', and two indexes, one named 'nid' on field 'nid' and one named 'node_title_type' on the field 'title' and the first four bytes of the field 'type':

$schema['node'] = array(
  'description' => 'The base table for nodes.',
  'fields' => array(
    'nid'       => array('type' => 'serial', 'unsigned' => TRUE, 'not null' => TRUE),
    'vid'       => array('type' => 'int', 'unsigned' => TRUE, 'not null' => TRUE,'default' => 0),
    'type'      => array('type' => 'varchar','length' => 32,'not null' => TRUE, 'default' => ''),
    'language'  => array('type' => 'varchar','length' => 12,'not null' => TRUE,'default' => ''),
    'title'     => array('type' => 'varchar','length' => 255,'not null' => TRUE, 'default' => ''),
    'uid'       => array('type' => 'int', 'not null' => TRUE, 'default' => 0),
    'status'    => array('type' => 'int', 'not null' => TRUE, 'default' => 1),
    'created'   => array('type' => 'int', 'not null' => TRUE, 'default' => 0),
    'changed'   => array('type' => 'int', 'not null' => TRUE, 'default' => 0),
    'comment'   => array('type' => 'int', 'not null' => TRUE, 'default' => 0),
    'promote'   => array('type' => 'int', 'not null' => TRUE, 'default' => 0),
    'moderate'  => array('type' => 'int', 'not null' => TRUE,'default' => 0),
    'sticky'    => array('type' => 'int', 'not null' => TRUE, 'default' => 0),
    'tnid'      => array('type' => 'int', 'unsigned' => TRUE, 'not null' => TRUE, 'default' => 0),
    'translate' => array('type' => 'int', 'not null' => TRUE, 'default' => 0),
  ),
  'indexes' => array(
    'node_changed'        => array('changed'),
    'node_created'        => array('created'),
    'node_moderate'       => array('moderate'),
    'node_frontpage'      => array('promote', 'status', 'sticky', 'created'),
    'node_status_type'    => array('status', 'type', 'nid'),
    'node_title_type'     => array('title', array('type', 4)),
    'node_type'           => array(array('type', 4)),
    'uid'                 => array('uid'),
    'tnid'                => array('tnid'),
    'translate'           => array('translate'),
  ),
  'unique keys' => array(
    'vid' => array('vid'),
  ),
  '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'),
);

See also

drupal_install_schema()

File

drupal/core/lib/Drupal/Core/Database/Schema.php, line 14
Definition of Drupal\Core\Database\Schema

Functions

Namesort descending Location Description
db_add_field drupal/core/includes/database.inc Adds a new field to a table.
db_add_index drupal/core/includes/database.inc Adds an index.
db_add_primary_key drupal/core/includes/database.inc Adds a primary key to a database table.
db_add_unique_key drupal/core/includes/database.inc Adds a unique key.
db_change_field drupal/core/includes/database.inc Changes a field definition.
db_create_table drupal/core/includes/database.inc Creates a new table from a Drupal table definition.
db_drop_field drupal/core/includes/database.inc Drops a field.
db_drop_index drupal/core/includes/database.inc Drops an index.
db_drop_primary_key drupal/core/includes/database.inc Drops the primary key of a database table.
db_drop_table drupal/core/includes/database.inc Drops a table.
db_drop_unique_key drupal/core/includes/database.inc Drops a unique key.
db_field_exists drupal/core/includes/database.inc Checks if a column exists in the given table.
db_field_names drupal/core/includes/database.inc Returns an array of field names from an array of key/index column specifiers.
db_field_set_default drupal/core/includes/database.inc Sets the default value for a field.
db_field_set_no_default drupal/core/includes/database.inc Sets a field to have no default value.
db_find_tables drupal/core/includes/database.inc Finds all tables that are like the specified base table name.
db_index_exists drupal/core/includes/database.inc Checks if an index exists in the given table.
db_rename_table drupal/core/includes/database.inc Renames a table.
db_table_exists drupal/core/includes/database.inc Checks if a table exists.
drupal_get_complete_schema drupal/core/includes/schema.inc Gets the whole database schema.
drupal_get_installed_schema_version drupal/core/includes/schema.inc Returns the currently installed schema version for a module.
drupal_get_schema drupal/core/includes/schema.inc Gets the schema definition of a table, or the whole database schema.
drupal_get_schema_unprocessed drupal/core/includes/schema.inc Returns the unprocessed and unaltered version of a module's schema.
drupal_get_schema_versions drupal/core/includes/schema.inc Returns an array of available schema versions for a module.
drupal_install_schema drupal/core/includes/schema.inc Creates all tables defined in a module's hook_schema().
drupal_schema_fields_sql drupal/core/includes/schema.inc Retrieves a list of fields from a table schema.
drupal_schema_get_field_value drupal/core/includes/schema.inc Typecasts values to proper datatypes.
drupal_set_installed_schema_version drupal/core/includes/schema.inc Updates the installed version information for a module.
drupal_uninstall_schema drupal/core/includes/schema.inc Removes all tables defined in a module's hook_schema().
drupal_write_record drupal/core/includes/schema.inc Saves (inserts or updates) a record to the database based upon the schema.
hook_schema drupal/core/modules/system/system.api.php Define the current version of the database schema.
hook_schema_alter drupal/core/modules/system/system.api.php Perform alterations to existing database schemas.
_db_create_keys_sql drupal/core/includes/database.inc
_drupal_schema_initialize drupal/core/includes/schema.inc Fills in required default values for table definitions from hook_schema().

Constants

Namesort descending Location Description
SCHEMA_INSTALLED drupal/core/includes/schema.inc Indicates that a module has been installed.
SCHEMA_UNINSTALLED drupal/core/includes/schema.inc Indicates that a module has not been installed yet.

Classes

Namesort descending Location Description
Schema drupal/core/lib/Drupal/Core/Database/Schema.php