Schema API
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 describing this table and its purpose. References to other tables should be enclosed in curly-brackets. For example, the node_revisions 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 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_revisions}.vid value for this nid."
- 'type': The generic datatype: 'varchar', 'int', 'serial' 'float', 'numeric', 'text', 'blob' or 'datetime'. 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.
- '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 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 '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.
- 'primary key': An array of one or more key column specifiers (see below) that form the primary key.
- 'unique key': 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.
- 'indexes': An associative array of indexes ('indexame' => specification). Each specification is an array of one or more key column specifiers (see below) that form an index on the table.
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(
'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' => ''),
'title' => array('type' => 'varchar', 'length' => 128, 'not null' => TRUE, 'default' => ''),
),
'primary key' => array('nid'),
'unique keys' => array(
'vid' => array('vid')
),
'indexes' => array(
'nid' => array('nid'),
'node_title_type' => array('title', array('type', 4)),
),
);
@see drupal_install_schema()
