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Data definition API

Since 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​

  • All the function calls in this page are public methods of the database manager, accessible from the $DB global object. You will need to "import" it within the upgrade function of your upgrade.php main function using the global keyword, for example:
function xmldb_xxxx_upgrade {
    global $DB;

    // Load the DDL manager and xmldb API.
    $dbman = $DB->get_manager();

    // Your upgrade code goes here
}
  • All of the $table, $field, and $index parameters are 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 we recommend examining the various core upgrade.php scripts.
tip

Always use the XMLDB Editor to modify your tables. It is capable of generating the PHP code required to make your definition changes.

danger

The use of these functions is restricted to the upgrade processes and it should not be used in any other parts of Moodle.

The functions​

Handling tables​

// Detect if a table exists.
$dbman->table_exists($table)

// Create a table.
$dbman->create_table($table, $continue = true, $feedback = true)

// Drop a table.
$dbman->drop_table($table, $continue = true, $feedback = true)

// Rename a table.
$dbman->rename_table($table, $newname, $continue = true, $feedback = true)

Handling fields​

// Detect if a field exists.
$dbman->field_exists($table, $field)

// Create a field.
$dbman->add_field($table, $field, $continue = true, $feedback = true)

// Drop a field.
$dbman->drop_field($table, $field, $continue = true, $feedback = true)

// Change the type of a field.
$dbman->change_field_type($table, $field, $continue = true, $feedback = true)

// Change the precision of a field.
$dbman->change_field_precision($table, $field, $continue = true, $feedback = true)

// Change the signed/unsigned status of a field.
$dbman->change_field_unsigned($table, $field, $continue = true, $feedback = true)

// Make a field nullable or not.
$dbman->change_field_notnull($table, $field, $continue = true, $feedback = true)

// Change the default value of a field.
$dbman->change_field_default($table, $field, $continue = true, $feedback = true)

// Rename a field.
$dbman->rename_field($table, $field, $newname, $continue = true, $feedback = true)

Handling indexes​

// Detect if an index exists.
$dbman->index_exists($table, $index)

// Return the name of an index in DB.
$dbman->find_index_name($table, $index)

// Add an index.
$dbman->add_index($table, $index, $continue = true, $feedback = true)

// Drop an index.
$dbman->drop_index($table, $index, $continue = true, $feedback = true)

Some considerations​

  1. The $table, $field, and $index parameters are, always, XMLDB objects.
  2. The $newtablename, and $newfieldname parameters are, always, simple strings.
  3. All the *_exists() functions always return a boolean value.
  4. If any issue is encountered during execution of these functions, an Exception will be thrown and the upgrade process will stop.
  5. Always use the XMLDB Editor to generate the PHP code automatically.

See also​