Selecting data using JDatabase/nl

Joomla! 

3.x

Joomla! 

2.5

Versie opmerking

Deze handleiding is opgesplitst in twee aparte delen:

• Invoegen, bijwerken en verwijderen van gegevens in de database.
• Selecteren van gegevens uit één of meer tabellen en het ophalen op diverse verschillende formaten.

Dit gedeelte van de documentatie kijkt naar het selecteren van gegevens uit een database tabel en het ophalen in verschillende formaten. Klik hier voor om het andere deel te lezen.

Inleiding

Joomla biedt een geavanceerde database abstractie laag om het gebruik door externe ontwikkelaars te vereenvoudigen. Nieuwe versies van de Joomla Platform API bieden extra functionaliteit welke de database laag verder uitbreidt en bevat functies zoals koppelingen naar een groot aantal database servers en de query-koppeling om de leesbaarheid te vergroten van verbindingscode an het vereenvoudigen van het coderen van SQL.

Joomla kan verschillende soorten SQL database systemen gebruiken en draaien op diverse omgevingen met verschillende tabel-voorvoegsels. Naast deze functies maakt de class automatisch de database verbinding aan. Naast het instantiëren van het object heeft u slechts twee regels code nodig om het resultaat uit de database te krijgen in een verscheidenheid aan formaten. Het gebruik van de Joomla database laag garandeert een maximum aan compatibiliteit en flexibiliteit voor uw extensie.

De query

Joomla's database querying veranderd met de introductie van Joomla 1.6. De aanbevolen manier van het bouwen van database queries is met behulp van "query chaining" (hoewel string queries nog wel worden ondersteund).

Query chaining verwijst naar de methode van koppelen van een aantal methodes, de één na de ander waarbij ieder methode een object terug geeft die de volgende methode kan ondersteunen, waardoor de leesbaarheid verbeterd wordt en de code vereenvoudigd.

Om een nieuwe instantie van de JDatabaseQuery class te verkrijgen gebruiken we de JDatabaseDriver getQuery methode:

$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.
$query->select($db->quoteName(array('user_id', 'profile_key', 'profile_value', 'ordering')));
$query->from($db->quoteName('#__user_profiles'));
$query->where($db->quoteName('profile_key') . ' LIKE '. $db->quote('\'custom.%\''));
$query->order('ordering ASC');

// 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(array('user_id', 'profile_key', 'profile_value', 'ordering')))
    ->from($db->quoteName('#__user_profiles'))
    ->where($db->quoteName('profile_key') . ' LIKE '. $db->quote('\'custom.%\''))
    ->order('ordering ASC');

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.

$query
    ->select( array('catid', 'COUNT(*)') )
    ->from($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(array('user_id', 'profile_key', 'profile_value', 'ordering')))
    ->from($db->quoteName('#__user_profiles'))
    ->setLimit('10');

Selecting Records from Multiple Tables

Using the JDatabaseQuery'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).

// Get a db connection.
$db = JFactory::getDbo();

// 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`
$query
    ->select(array('a.*', 'b.username', 'b.name'))
    ->from($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 \'a%\'')
    ->order($db->quoteName('a.created') . ' DESC');

// 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 \'a%\'')
    ->order($db->quoteName('a.created') . ' DESC');

Notice how chaining makes the source code much 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') . ' ON (' . $db->quoteName('a.created_by') . ' = ' . $db->quoteName('b.id') . ')')
    ->where($db->quoteName('b.username') . ' LIKE \'a%\'')
    ->order($db->quoteName('a.created') . ' DESC');

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:

$query
    ->select(array('a.*'))
    ->select($db->quoteName(array('b.username', 'b.name'), array('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 \'a%\'')
    ->order($db->quoteName('a.created') . ' DESC');

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 a number of records:

$db = JFactory::getDbo();
$query = $db->getQuery(true);
$query->select('COUNT(*)');
$query->from($db->quoteName('#__my_table'));
$query->where($db->quoteName('name')." = ".$db->quote($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).

$db = JFactory::getDbo();
$query = $db->getQuery(true);
$query->select('field_name');
$query->from($db->quoteName('#__my_table'));
$query->where($db->quoteName('some_name')." = ".$db->quote($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