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Data definition API

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Moodle 2.0

In this page you'll access to the available functions under Moodle to be able to handle DB structures (tables, fields, indexes...).

The objective is to have a well-defined group of functions able to handle all the DB structure (DDL statements) using one neutral description, being able to execute the correct SQL statements required by each RDBMS. All these functions are used exclusively by the installation and upgrade processes.

In this page you'll see a complete list of such functions, with some explanations, tricks and examples of their use. If you are interested, it's also highly recommendable to take a look to the DML functions page where everything about how to handle DB data (select, insert, update, delete i.e. DML statements) is defined.

Of course, feel free to clarify, complete and add more info to all this documentation. It will be welcome, absolutely!

Main info

Important note: All the functions showed in this page are for use in Moodle 2.0 upwards, where we changed the DB layer to support some new features. If you need information for previous Moodle version, take a look to the DDL functions - pre 2.0 page. For a detailed reference of changes, see the migration docs.

  • All the function calls in this page are public methods of the database manager, accessible from the $DB global object. So you'll need to "import" it within your upgrade.php main function with something like:
function xmldb_xxxx_upgrade {
    global $DB;
    $dbman = $DB->get_manager(); // loads ddl manager and xmldb classes
    /// Your upgrade code goes here
  • Once more, the use of these functions is restricted to the upgrade processes and it shouldn't be used ever out from there.
  • All the $table, $field, $index parameters are, always, XMLDB objects. Don't forget to read carefully the complete documentation about creating new DDL functions before playing with these functions. Everything is explained there, with one general example and some really useful tricks to improve the use of all the functions detailed below.
  • If you want real examples of the usage of these functions it's 100% interesting to examine the upgrade.php scripts that are responsible for Moodle upgrading since the 1.7 release.
  • Also, it's a very good idea (highly recommended!) to use the XMLDB Editor itself to generate automatically the desired PHP code. Just play with it!

The functions

Handling tables

/// To detect if one table exists:

/// To create one table:
    $dbman->create_table($table, $continue=true, $feedback=true)

/// To drop one table:
    $dbman->drop_table($table, $continue=true, $feedback=true)

/// To rename one table:
    $dbman->rename_table($table, $newname, $continue=true, $feedback=true)

Handling fields

/// To detect if one field exists:
    $dbman->field_exists($table, $field)

/// To create one field:
    $dbman->add_field($table, $field, $continue=true, $feedback=true)

/// To drop one field:
    $dbman->drop_field($table, $field, $continue=true, $feedback=true)

/// To change the type of one field:
    $dbman->change_field_type($table, $field, $continue=true, $feedback=true)

/// To change the precision of one field:
    $dbman->change_field_precision($table, $field, $continue=true, $feedback=true)

/// To change the signed/unsigned status of one field:
    $dbman->change_field_unsigned($table, $field, $continue=true, $feedback=true)

/// To make one field nullable or not:
    $dbman->change_field_notnull($table, $field, $continue=true, $feedback=true)

/// To drop one enum (check constraint) from one field:
/// (note this function will be only available in Moodle 2.0 as it's needed
/// to drop any enum existing in previous Moodle releases). Will be out in Moodle 2.1
    $dbman->drop_enum_from_field($table, $field, $continue=true, $feedback=true)

/// To change the default value of one field:
    $dbman->change_field_default($table, $field, $continue=true, $feedback=true)

/// To rename one field:
    $dbman->rename_field($table, $field, $newname, $continue=true, $feedback=true)

Handling indexes

/// To detect if one index exists:
    $dbman->index_exists($table, $index)

/// To return the name of one index in DB:
    $dbman->find_index_name($table, $index)

/// To add one index:
    $dbman->add_index($table, $index, $continue=true, $feedback=true)

/// To drop one index:
    $dbman->drop_index($table, $index, $continue=true, $feedback=true)

Some considerations

  1. All the $table, $field, $index parameters are, always, XMLDB objects.
  2. All the $newtablename, $newfieldname parameters are, always, simple strings.
  3. All the ***_exists() functions return boolean true/false.
  4. Any problem in the execution of the functions will throw one Exception and the upgrade process will die.
  5. It's recommendable to use the XMLDB Editor to generate the PHP code automatically (did I say this before? :-P )

See also