The Schema API

Submitted by elyzium on Tue, 2019-03-26 09:44

Drupal supports multiple databases (MySQL, PostreSQL, SQLite, etc.) through its database abstraction
layer. Each module that wants to have a database table describes that table to Drupal using a schema
definition. Drupal then translates the definition into syntax that is appropriate for the database.

when you write a module that needs to create one or more database tables for
storage, the instructions to create and maintain the table structure go into an .install file that is
distributed with the module

During the installation of a new module, Drupal automatically checks to see whether a schema
definition exists in the modules .install file, If a schema definition exists, Drupal
creates the database table(s) defined within the schema. The following example demonstrates the
general structure of a schema definition.

$schema['tablename'] = array(
// Table description.
'description' => t('Description of what the table is used for.'),
'fields' => array(
// Field definition.
'field1' => array(
'type' => 'int',
'unsigned' => TRUE,
'not null' => TRUE,
'default' => 0,
'description' => t('Description of what this field is used for.'),
),
),
// Index declarations.
'primary key' => array('field1'),
);

Field Type Mapping from Schema to Database

1.Varchar
The varchar, or variable length character field, is the most frequently used field type for storing text less
than 256 characters in length. A maximum length, in characters, is defined by the length key. MySQL
varchar field lengths are 0–255 characters (MySQL 5.0.2 and earlier) and 0–65,535 characters (MySQL
5.0.3 and later); PostgreSQL varchar field lengths may be larger.

$field['fieldname'] = array(
'type' => 'varchar', // Required.
'length' => 255, // Required.
'not null' => TRUE, // Defaults to FALSE.
'default' => 'chocolate', // See below.
'description' => t('Always state the purpose of your field.'),
);

If the default key has not been set and the not null key has been set to FALSE, the default will be set
to NULL.

2.Char
Char fields are fixed-length character fields. The length of the field, in characters, is defined by the
length key. MySQL char field lengths are 0–255 characters.

$field['fieldname'] = array(
'type' => 'char', // Required.
'length' => 64, // Required.
'not null' => TRUE, // Defaults to FALSE.
'default' => 'strawberry', // See below.
'description' => t('Always state the purpose of your field.'),
);

If the default key has not been set and the not null key has been set to FALSE, the default will be set
to NULL.

3.Text
Text fields are used for textual data that can be quite large. For example, the body field of the
node_revisions table (where node body text is stored) is of this type. Default values may not be used for
text fields.

$field['fieldname'] = array(
'type' => 'text', // Required.
'size' => 'small', // tiny | small | normal | medium | big
'not null' => TRUE, // Defaults to FALSE.
'description' => t('Always state the purpose of your field.'),
);

4. Integer
This field type is used for storing integers, such as node IDs. If the unsigned key is TRUE, negative integers
will not be allowed.

$field['fieldname'] = array(
'type' => 'int', // Required.
'unsigned' => TRUE, // Defaults to FALSE.
'size' => 'small', // tiny | small | medium | normal | big
'not null' => TRUE, // Defaults to FALSE.
'description' => t('Always state the purpose of your field.'),
);

5.Serial
A serial field keeps a number that increments. For example, when a node is added, the nid field of the
node table is incremented. This is done by inserting a row and calling db_last_insert_id(). If a row is
added by another thread between the insertion of a row and the retrieval of the last ID, the correct ID is
still returned because it is tracked on a per-connection basis. A serial field must be indexed; it is usually
indexed as the primary key.

$field['fieldname'] = array(
'type' => 'serial', // Required.
'unsigned' => TRUE, // Defaults to FALSE. Serial numbers are usually positive.
'size' => 'small', // tiny | small | medium | normal | big
'not null' => TRUE, // Defaults to FALSE. Typically TRUE for serial fields.
'description' => t('Always state the purpose of your field.'),
);

6. Date and Time: Datetime
The Drupal core does not use this data type, preferring to use Unix timestamps in integer fields. The
datetime format is a combined format containing both the date and the time.

$field['fieldname'] = array(
'type' => 'datetime', // Required.
'not null' => TRUE, // Defaults to FALSE.
'description' => t('Always state the purpose of your field.'),
);

7.Binary: Blob
The binary large object data (blob) type is used to store binary data (for example, Drupal’s cache table to
store the cached data). Binary data may include music, images, or video. Two sizes are available, normal
and big.

$field['fieldname'] = array(
'type' => 'blob', // Required.
'size' => 'normal' // normal | big
'not null' => TRUE, // Defaults to FALSE.
'description' => t('Always state the purpose of your field.'),
);

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Rickyapalk (not verified)

Wed, 2019-12-04 08:28

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