Developer FAQ

Revision as of 13:05, 9 July 2009 by Helen Foster (talk | contribs) (what is HEAD (thanks to Tim for his answer copied from Development talk:Places to search for lang strings))

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Help for new coders

Where can I start?

See Finding your way into the Moodle code.

Where can "newbies" to Moodle get help?

The General developer forum! Feel free to ask any question, no matter how basic or advanced. Many people ask different levels of question every day, and the community is generally welcoming and quick to respond.

How do I create a patch?

See How to create a patch.

Is there any information on creating a new module or plugin?

See Modules, Blocks and Authentication plugins, or the full list of plugin types.

Is there any information on backup and restore?

See Backup.

I can't use one of the available plug-in points to make my change. What alternative is there?

See Local customisation.

Moodle's database

Where can I see a schema for the structure of the Moodle database?

Database_schema_introduction gives a high level overview of the database schema.

Because of Moodle's modular nature, there is no single, detailed representation of the full database schema. Instead, the tables for each part of Moodle are defined in a database-neutral XML format, see XMLDB, in each part of moodle. Look for files called install.xml in folders called db throughout the code. Alternatively, from Moodle 2.0 onwards, go to Administration -> Development -> XMLDB editor, and use the [Doc] links to see automatically generated documentation built form the comments in the install.xml files.

How to get/set information when writing new Moodle code

How do I find out the currently-logged-on user?

The global object $USER, which contains the numeric $USER->id among other things.

How do I find out the current course?

The global object $COURSE, which contains the numeric $COURSE->id

How do I insert/retrieve records in the database, without creating my own database connections?

Always use the "datalib" functions, such as insert_record() or get_record(). Since Moodle 1.7 these are found in lib/dmllib.php. Using these functions helps with database abstraction (e.g. running on either MySQL or Postgres) as well as maintaining a single database connection. Moodle uses ADODB for database abstraction.

Look at the documentation for datalib.php for the list of functions and details of use.

How do I get/set configuration settings?

To get config values you would typically access the global $CFG object directly, which is automatically created by the core Moodle scripts. To set these "main" config values use set_config($name, $value). The values are stored in the Moodle "config" database table, but these functions take care of cacheing on your behalf, so you should always use these rather than fetching the records directly.

There is also a second table of config settings specifically for plugins ("config_plugin"). These are not automatically loaded into the $CFG object, so to fetch these you would use get_config($plugin, $name). To set them use set_config($name, $value, $plugin).

On top of those global configuration values, individual blocks may also have configuration "object" associated with it (the data is serialized and stored in the "block_instance" table). Within blocks, this data is automatically loaded into the config attribute of the block.

What is 'HEAD'?

HEAD is version control jargon for the latest version, so at the moment it means Moodle 2.0 dev version. (After the Moodle 2.0 stable branch is made, HEAD will mean 2.1 dev). Look for example, at the links at the top of You can get it from and install it if you want to play.

See also