J4.x:Selecting data using JDatabase

Joomla! 

4.x

Version Note

This tutorial is split into two independent parts:

• Inserting, updating and removing data from the database.
• Selecting data from one or more tables and retrieving it in a variety of different forms

This section of the documentation looks at selecting data from a database table and retrieving it in a variety of formats. To see the other part click here

Introduction

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 Query

Since Joomla introduced support for a variety of database types in Joomla 1.6 - the recommended way of building database queries is through "query chaining" (although string queries will always be 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 \Joomla\Database\DatabaseQuery class we use the \Joomla\Database\DatabaseDriver getQuery method:

use Joomla\CMS\Factory;

// When used in the component's Model
$db = $this->getDatabase();

// When used in other places 
$db = Factory::getContainer()->get('DatabaseDriver');

$query = $db->getQuery(true);

Do NOT use the following Joomla 3 method anymore because it is deprecated:

$db = Factory::getDbo();

The \Joomla\Database\DatabaseDriver::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 \Joomla\Database\DatabaseQuery 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 \Joomla\Database\DatabaseQuery class. Using the select, from, where and order methods, we can create queries which are flexible, easily readable and portable:

use Joomla\CMS\Factory;

// Get a db connection.
$db = Factory::getContainer()->get('DatabaseDriver');

// 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.
$query->select($db->quoteName(['user_id', 'profile_key', 'profile_value', 'ordering']));
$query->from($db->quoteName('#__user_profiles'));
$query->where($db->quoteName('profile_key') . ' LIKE :profile_key');
$query->order($db->quoteName('ordering') . ' ASC');

// bind value for prepared statements
$query->bind(':profile_key', 'custom.%');

// Reset the query using our newly populated query object.
$db->setQuery($query);

// Load the results as a list of stdClass objects (see later for more options on retrieving data).
$results = $db->loadObjectList();

The query can also be chained to simplify further:

$query
    ->select($db->quoteName(['user_id', 'profile_key', 'profile_value', 'ordering']))
    ->from($db->quoteName('#__user_profiles'))
    ->where($db->quoteName('profile_key') . ' LIKE :profile_key')
    ->order($db->quoteName('ordering') . ' ASC')
    ->bind(':profile_key', 'custom.%');

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

Grouping can be achieved simply too. The following query would count the number of articles in each category.

$query
    ->select( ['catid', 'COUNT(*)'] )
    ->from($db->quoteName('#__content'))
    ->group($db->quoteName('catid'));

A limit can be set to a query using "setLimit". For example in the following query, it would return up to 10 records.

$query
    ->select($db->quoteName(['user_id', 'profile_key', 'profile_value', 'ordering']))
    ->from($db->quoteName('#__user_profiles'))
    ->setLimit('10');

Selecting Records from Multiple Tables

Using the \Joomla\Database\DatabaseQuery's join methods, we can select records from multiple related tables. The generic "join" method takes two arguments: the join "type" (inner, outer, left, right) and the join condition. In the following example you will notice that we can use all of the keywords we would normally use if we were writing a native SQL query, including the AS keyword for aliasing tables and the ON keyword for creating relationships between tables. Also note that the table alias is used in all methods which reference table columns (I.e. select, where, order).

use Joomla\CMS\Factory;

// Get a db connection.
$db = Factory::getContainer()->get('DatabaseDriver');

// Create a new query object.
$query = $db->getQuery(true);

// Select all articles for users who have a username which starts with 'a'.
// Order it by the created date.
// Note by putting 'a' as a second parameter will generate `#__content` AS `a`
$query
    ->select(['a.*', 'b.username', 'b.name'])
    ->from($db->quoteName('#__content', 'a'))
    ->join('INNER', $db->quoteName('#__users', 'b') . ' ON (' . $db->quoteName('a.created_by') . ' = ' . $db->quoteName('b.id') . ')')
    ->where($db->quoteName('b.username') . ' LIKE :username')
    ->order($db->quoteName('a.created') . ' DESC')
    ->bind(':username', 'a%');

// Reset the query using our newly populated query object.
$db->setQuery($query);

// Load the results as a list of stdClass objects (see later for more options on retrieving data).
$results = $db->loadObjectList();

The join method above enables us to query both the content and user tables, retrieving articles with their author details. There are also convenience methods for joins:

• innerJoin()
• leftJoin()
• rightJoin()
• outerJoin()

We can use multiple joins to query across more than two tables:

$query
    ->select(array('a.*', 'b.username', 'b.name', 'c.*', 'd.*'))
    ->from($db->quoteName('#__content', 'a'))
    ->join('INNER', $db->quoteName('#__users', 'b') . ' ON (' . $db->quoteName('a.created_by') . ' = ' . $db->quoteName('b.id') . ')')
    ->join('LEFT', $db->quoteName('#__user_profiles', 'c') . ' ON (' . $db->quoteName('b.id') . ' = ' . $db->quoteName('c.user_id') . ')')
    ->join('RIGHT', $db->quoteName('#__categories', 'd') . ' ON (' . $db->quoteName('a.catid') . ' = ' . $db->quoteName('d.id') . ')')
    ->where($db->quoteName('b.username') . ' LIKE :username')
    ->order($db->quoteName('a.created') . ' DESC')
    ->bind(':username', 'a%');

Notice how chaining makes the source code more readable for these longer queries.

In some cases, you will also need to use the AS clause when selecting items to avoid column name conflicts. In this case, multiple select statements can be chained in conjunction with using the second parameter of $db->quoteName.

$query
    ->select('a.*')
    ->select($db->quoteName('b.username', 'username'))
    ->select($db->quoteName('b.name', 'name'))
    ->from($db->quoteName('#__content', 'a'))
    ->join('INNER', $db->quoteName('#__users', 'b'), $db->quoteName('a.created_by') . ' = ' . $db->quoteName('b.id'))
    ->where($db->quoteName('b.username') . ' LIKE :username')
    ->order($db->quoteName('a.created') . ' DESC')
    ->bind(':username', 'a%');

A second array can also be used as the second parameter of the select statement to populate the values of the AS clause. Remember to include nulls in the second array to correspond to columns in the first array that you don't want to use the AS clause for:

$query
    ->select(['a.*'])
    ->select($db->quoteName(array('b.username', 'b.name'), ['username', 'name']))
    ->from($db->quoteName('#__content', 'a'))
    ->join('INNER', $db->quoteName('#__users', 'b') . ' ON (' . $db->quoteName('a.created_by') . ' = ' . $db->quoteName('b.id') . ')')
    ->where($db->quoteName('b.username') . ' LIKE :username')
    ->order($db->quoteName('a.created') . ' DESC')
    ->bind(':username', 'a%');

Using Prepared Statements

With Joomla! 4.0 we have moved all queries to use prepared statements. For easier use of prepared statements we introduced some helper functions and allow to use arrays in several function calls. Simple query with prepared statements.

$query = $this->db->getQuery(true)
	->select($this->db->quoteName(array('id', 'password')))
	->from($this->db->quoteName('#__users'))
	->where($this->db->quoteName('username') . ' = :username')
	->bind(':username', $credentials['username']);

You see that we don't add the $credentials['username'] directly to the query, instead we add the placeholder :username into the query and bind the variable to the query. When we bind a variable to a query we don't need to escape nor to quote it. Beware that binding a variable will always be a reference. A nice side effect of this, is that you can manipulate the query in a loop.

$listOfUsernames = [ 'admin', 'user1' ];

$query = $this->db->getQuery(true)
	->select($this->db->quoteName(array('id', 'password')))
	->from($this->db->quoteName('#__users'))
	->where($this->db->quoteName('username') . ' = :username')
	->bind(':username', $username);

foreach($listOfUsernames as $name)
{
  $username = $name;
  $this->db->setQuery($query);
  $user = $this->db->loadObject();
  print_r($user);
}

In the loop we set the previously bound $username variable with the $name variable from the loop, then we have to set the query again (because Joomla resets the database driver after query execution which is only true for load* functions). The result will be multiple queries with different username values. We can use arrays to add multiple variables at once.

$query = $this->db->getQuery(true)
	->select($this->db->quoteName(array('id', 'password')))
	->from($this->db->quoteName('#__users'))
	->where($this->db->quoteName('username') . ' = :username')
	->where($this->db->quoteName('id') . ' = :id')
	->bind([':username', ':id'], [$credentials['username'], 42], [Joomla\Database\ParameterType::STRING, Joomla\Database\ParameterType::INTEGER]);

We add username and id as bind parameter and set the correct ParameterType for each variable. It's also possible to use one variable for all bind values and ParameterTypes.

$query = $this->db->getQuery(true)
	->select($this->db->quoteName(array('id', 'password')))
	->from($this->db->quoteName('#__users'))
	->where($this->db->quoteName('username') . ' = :username')
	->where($this->db->quoteName('password') . ' = :password')
	->bind([':username', ':password'], $credentials['username']);

The parameter :username and :password get set to the same value and the default ParameterType. The function whereIn() and whereNotIn() always use prepared statements, internal these functions uses the bindArray function. It can be used to bind an array of variables without specifying the placeholder.

$userids = [1,2,3,4];

$query = $this->db->getQuery(true)
	->select($this->db->quoteName(array('id', 'password')))
	->from($this->db->quoteName('#__users'));

$parameterNames = $query->bindArray($userids);

$query->where($this->db->quoteName('id') . ' IN (' . implode(',', $parameterNames) . ')');

The bindArray function returns an array of placeholders. The index is unique for the whole query.

$placeholders = [
  ':preparedArray1',
  ':preparedArray2',
  ':preparedArray3',
  ':preparedArray4'
];

Query Results

The database class contains many methods for working with a query's result set.

Single Value Result

loadResult()

Use loadResult() when you expect just a single value back from your database query.

id	name	email	username
1	John Smith	johnsmith@domain.example	johnsmith
2	Magda Hellman	magda_h@domain.example	magdah
3	Yvonne de Gaulle	ydg@domain.example	ydegaulle

This is often the result of a 'count' query to get the number of records:

use Joomla\CMS\Factory;
$db = Factory::getContainer()->get('DatabaseDriver');
$query = $db->getQuery(true);
$query->select('COUNT(*)');
$query->from($db->quoteName('#__my_table'));
$query->where($db->quoteName('name')." = :value");
$query->bind('value', $value)

// Reset the query using our newly populated query object.
$db->setQuery($query);
$count = $db->loadResult();

or where you are just looking for a single field from a single row of the table (or possibly a single field from the first row returned).

use Joomla\CMS\Factory;
$db = Factory::getContainer()->get('DatabaseDriver');
$query = $db->getQuery(true);
$query->select('field_name');
$query->from($db->quoteName('#__my_table'));
$query->where($db->quoteName('some_name')." = :value");
$query->bind(':value', $some_value);

$db->setQuery($query);
$result = $db->loadResult();

Single Row Results

Each of these results functions will return a single record from the database even though there may be several records that meet the criteria that you have set. To get more records, you need to call the function again.

id	name	email	username
1	John Smith	johnsmith@domain.example	johnsmith
2	Magda Hellman	magda_h@domain.example	magdah
3	Yvonne de Gaulle	ydg@domain.example	ydegaulle

loadRow()

loadRow() returns an indexed array from a single record in the table:

. . .
$db->setQuery($query);
$row = $db->loadRow();
print_r($row);

will give:

Array ( [0] => 1, [1] => John Smith, [2] => johnsmith@domain.example, [3] => johnsmith ) 

You can access the individual values by using:

$row['index'] // e.g. $row['2']

Notes:

1. The array indices are numeric starting from zero.
2. Whilst you can repeat the call to get further rows, one of the functions that returns multiple rows might be more useful.

loadAssoc()

loadAssoc() returns an associated array from a single record in the table:

. . .
$db->setQuery($query);
$row = $db->loadAssoc();
print_r($row);

will give:

Array ( [id] => 1, [name] => John Smith, [email] => johnsmith@domain.example, [username] => johnsmith )

You can access the individual values by using:

$row['name'] // e.g. $row['email']

Notes:

1. Whilst you can repeat the call to get further rows, one of the functions that returns multiple rows might be more useful.

loadObject()

loadObject returns a PHP object from a single record in the table:

. . .
$db->setQuery($query);
$result = $db->loadObject();
print_r($result);

will give:

stdClass Object ( [id] => 1, [name] => John Smith, [email] => johnsmith@domain.example, [username] => johnsmith )

You can access the individual values by using:

$result->index // e.g. $result->email

Notes:

1. Whilst you can repeat the call to get further rows, one of the functions that returns multiple rows might be more useful.

Single Column Results

Each of these results functions will return a single column from the database.

id	name	email	username
1	John Smith	johnsmith@domain.example	johnsmith
2	Magda Hellman	magda_h@domain.example	magdah
3	Yvonne de Gaulle	ydg@domain.example	ydegaulle

loadColumn()

loadColumn() returns an indexed array from a single column in the table:

$query->select('name'));
      ->from . . .";
. . .
$db->setQuery($query);
$column= $db->loadColumn();
print_r($column);

will give:

Array ( [0] => John Smith, [1] => Magda Hellman, [2] => Yvonne de Gaulle )

You can access the individual values by using:

$column['index'] // e.g. $column['2']

Notes:

1. The array indices are numeric starting from zero.
2. loadColumn() is equivalent to loadColumn(0).

loadColumn($index)

loadColumn($index) returns an indexed array from a single column in the table:

$query->select(array('name', 'email', 'username'));
      ->from . . .";
. . .
$db->setQuery($query);
$column= $db->loadColumn(1);
print_r($column);

will give:

Array ( [0] => johnsmith@domain.example, [1] => magda_h@domain.example, [2] => ydg@domain.example )

You can access the individual values by using:

$column['index'] // e.g. $column['2']

loadColumn($index) allows you to iterate through a series of columns in the results:

. . .
$db->setQuery($query);
for ( $i = 0; $i <= 2; $i++ ) {
  $column = $db->loadColumn($i);
  print_r($column);
}

will give:

Array ( [0] => John Smith, [1] => Magda Hellman, [2] => Yvonne de Gaulle ),
Array ( [0] => johnsmith@domain.example, [1] => magda_h@domain.example, [2] => ydg@domain.example ),
Array ( [0] => johnsmith, [1] => magdah, [2] => ydegaulle )

Notes:

1. The array indices are numeric starting from zero.

Multi-Row Results

Each of these results functions will return multiple records from the database.

id	name	email	username
1	John Smith	johnsmith@domain.example	johnsmith
2	Magda Hellman	magda_h@domain.example	magdah
3	Yvonne de Gaulle	ydg@domain.example	ydegaulle

loadRowList()

loadRowList() returns an indexed array of indexed arrays from the table records returned by the query:

. . .
$db->setQuery($query);
$row = $db->loadRowList();
print_r($row);

will give (with line breaks added for clarity):

Array (
[0] => Array ( [0] => 1, [1] => John Smith, [2] => johnsmith@domain.example, [3] => johnsmith ),
[1] => Array ( [0] => 2, [1] => Magda Hellman, [2] => magda_h@domain.example, [3] => magdah ),
[2] => Array ( [0] => 3, [1] => Yvonne de Gaulle, [2] => ydg@domain.example, [3] => ydegaulle )
)

You can access the individual rows by using:

$row['index'] // e.g. $row['2']

and you can access the individual values by using:

$row['index']['index'] // e.g. $row['2']['3']

Notes:

1. The array indices are numeric starting from zero.

loadAssocList()

loadAssocList() returns an indexed array of associated arrays from the table records returned by the query:

. . .
$db->setQuery($query);
$row = $db->loadAssocList();
print_r($row);

will give (with line breaks added for clarity):

Array (
[0] => Array ( [id] => 1, [name] => John Smith, [email] => johnsmith@domain.example, [username] => johnsmith ),
[1] => Array ( [id] => 2, [name] => Magda Hellman, [email] => magda_h@domain.example, [username] => magdah ),
[2] => Array ( [id] => 3, [name] => Yvonne de Gaulle, [email] => ydg@domain.example, [username] => ydegaulle )
) 

You can access the individual rows by using:

$row['index'] // e.g. $row['2']

and you can access the individual values by using:

$row['index']['column_name'] // e.g. $row['2']['email']

loadAssocList($key)

loadAssocList('key') returns an associated array - indexed on 'key' - of associated arrays from the table records returned by the query:

. . .
$db->setQuery($query);
$row = $db->loadAssocList('username');
print_r($row);

will give (with line breaks added for clarity):

Array (
[johnsmith] => Array ( [id] => 1, [name] => John Smith, [email] => johnsmith@domain.example, [username] => johnsmith ),
[magdah] => Array ( [id] => 2, [name] => Magda Hellman, [email] => magda_h@domain.example, [username] => magdah ),
[ydegaulle] => Array ( [id] => 3, [name] => Yvonne de Gaulle, [email] => ydg@domain.example, [username] => ydegaulle )
)

You can access the individual rows by using:

$row['key_value'] // e.g. $row['johnsmith']

and you can access the individual values by using:

$row['key_value']['column_name'] // e.g. $row['johnsmith']['email']

Note: Key must be a valid column name from the table; it does not have to be an Index or a Primary Key. But if it does not have a unique value you may not be able to retrieve results reliably.

loadAssocList($key, $column)

loadAssocList('key', 'column') returns an associative array, indexed on 'key', of values from the column named 'column' returned by the query:

. . .
$db->setQuery($query);
$row = $db->loadAssocList('id', 'username');
print_r($row);

will give (with line breaks added for clarity):

Array (
[1] => John Smith,
[2] => Magda Hellman,
[3] => Yvonne de Gaulle,
)

Note: Key must be a valid column name from the table; it does not have to be an Index or a Primary Key. But if it does not have a unique value you may not be able to retrieve results reliably.

loadObjectList()

loadObjectList() returns an indexed array of PHP objects from the table records returned by the query:

. . .
$db->setQuery($query);
$row = $db->loadObjectList();
print_r($row);

will give (with line breaks added for clarity):

Array (
[0] => stdClass Object ( [id] => 1, [name] => John Smith,
    [email] => johnsmith@domain.example, [username] => johnsmith ),
[1] => stdClass Object ( [id] => 2, [name] => Magda Hellman,
    [email] => magda_h@domain.example, [username] => magdah ),
[2] => stdClass Object ( [id] => 3, [name] => Yvonne de Gaulle,
    [email] => ydg@domain.example, [username] => ydegaulle )
)

You can access the individual rows by using:

$row['index'] // e.g. $row['2']

and you can access the individual values by using:

$row['index']->name // e.g. $row['2']->email

loadObjectList($key)

loadObjectList('key') returns an associated array - indexed on 'key' - of objects from the table records returned by the query:

. . .
$db->setQuery($query);
$row = $db->loadObjectList('username');
print_r($row);

will give (with line breaks added for clarity):

Array (
[johnsmith] => stdClass Object ( [id] => 1, [name] => John Smith,
    [email] => johnsmith@domain.example, [username] => johnsmith ),
[magdah] => stdClass Object ( [id] => 2, [name] => Magda Hellman,
    [email] => magda_h@domain.example, [username] => magdah ),
[ydegaulle] => stdClass Object ( [id] => 3, [name] => Yvonne de Gaulle,
    [email] => ydg@domain.example, [username] => ydegaulle )
)

You can access the individual rows by using:

$row['key_value'] // e.g. $row['johnsmith']

and you can access the individual values by using:

$row['key_value']->column_name // e.g. $row['johnsmith']->email

Note: Key must be a valid column name from the table; it does not have to be an Index or a Primary Key. But if it does not have a unique value you may not be able to retrieve results reliably.

Miscellaneous Result Set Methods

getNumRows()

getNumRows() will return the number of result rows found by the last SELECT or SHOW query and waiting to be read. To get a result from getNumRows() you have to run it after the query and before you have retrieved any results. To retrieve the number of rows affected by a INSERT, UPDATE, REPLACE or DELETE query, use getAffectedRows().

. . .
$db->setQuery($query);
$db->execute();
$num_rows = $db->getNumRows();
print_r($num_rows);
$result = $db->loadRowList();

will return

3

Note: getNumRows() is only valid for statements like SELECT or SHOW that return an actual result set. If you run getNumRows() after loadRowList() - or any other retrieval method - you will get a PHP Warning:

Warning: mysql_num_rows(): 80 is not a valid MySQL result resource
in libraries\joomla\database\database\mysql.php on line 344

See Also

• Joomla! Programmers Documentation: Secure DB Queries
• Inserting, Updating and Removing data using JDatabase
• Moving Joomla To Prepared Statements
• Using the union methods in database queries (Joomla! 3.3+)
• The PHP Manual on Prepared statements
• Joomla Framework API