Accessing the database using JDatabase

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Joomla provides a sophisticated database abstraction layer to simplify the usage for third party developers. New versions of the Joomla Platform API provide additional functionality which extends the database layer further, and includes features such as connectors to a greater variety of database servers and the query chaining to improve readability of connection code and simplify SQL coding.



Joomla can use different kinds of SQL database systems and run in a variety of environments with different table-prefixes. In addition to these functions, the class automatically creates the database connection. Besides instantiating the object you need just two lines of code to get a result from the database in a variety of formats. Using the Joomla database layer ensures a maximum of compatibility and flexibility for your extension.

The Connection

Joomla supports a generic interface for connecting to the database, hiding the intricacies of a specific database server from the Framework developer, thus making Joomla code easier to port from one database to another.

To obtain a database connection, use the JFactory getDbo static method:

$db = JFactory::getDbo();

Alternatively, if your class inherits from the JModel (or a decendent class) getDbo method:

$db = $this->getDbo();

Joomla 3.0 users should note that the JModel class has been renamed JModelLegacy and will eventually be deprecated in favour of the class JModelBase. Therefore, any Joomla 3.0 core or extension code should use JFactory::getDbo() to obtain a database connection.

The Query

Joomla's database querying has changed since the new Joomla Framework was introduced "query chaining" is now the recommended method for building database queries (although string queries are still supported).

Query chaining refers to a method of connecting a number of methods, one after the other, with each method returning an object that can support the next method, improving readability and simplifying code.

To obtain a new instance of the JDatabaseQuery class we use the JDatabaseDriver getQuery method:

$db = JFactory::getDbo();
$query = $db->getQuery(true);

The JDatabaseDriver::getQuery takes an optional argument, $new, which can be true or false (the default being false).

To query our data source we can call a number of JDatabaseQuery methods; these methods encapsulate the data source's query language (in most cases SQL), hiding query-specific syntax from the developer and increasing the portability of the developer's source code.

Some of the more frequently used methods include; select, from, join, where and order. There are also methods such as insert, update and delete for modifying records in the data store. By chaining these and other method calls, you can create almost any query against your data store without compromising portability of your code.

Selecting Records from a Single Table

Below is an example of creating a database query using the JDatabaseQuery class. Using the select, from, where and order methods, we can create queries which are flexible, easily readable and portable:

// Get a db connection.
$db = JFactory::getDbo();
// Create a new query object.
$query = $db->getQuery(true);
// Select all records from the user profile table where key begins with "custom.".
// Order it by the ordering field.
$query->select(array('user_id', 'profile_key', 'profile_value', 'ordering'));
$query->where('profile_key LIKE \'custom.%\'');
$query->order('ordering ASC');
// Reset the query using our newly populated query object.
// Load the results as a list of stdClass objects.
$results = $db->loadObjectList();

The query can also be chained to simplify further:

    ->select(array('user_id', 'profile_key', 'profile_value', 'ordering'))
    ->where('profile_key LIKE \'custom.%\'')
    ->order('ordering ASC');

Chaining can become useful when queries become longer and more complex.

Selecting Records from Multiple Tables

Inserting a Record

Updating a Record

Deleting a Record