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Difference between revisions of "Accessing the database using JDatabase"

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(Subqueries: See http://docs.joomla.org/index.php?title=Talk:How_to_use_the_database_classes_in_your_script&oldid=36844#Subqueries)
(Useful information: Corrected punctuation and added missing space.)
(32 intermediate revisions by 12 users not shown)
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Joomla provides a sophisticated database abstraction layer to simplify the usage for third party developers. This guide will help you use this layer.
+
{{version/tutor|2.5,3.1}}
 +
==Useful information==
 +
Being able to use JDatabase is vital when you start developing for Joomla. The tutorial is split into two independent parts:
 +
* [[Inserting, Updating and Removing data using JDatabase|Inserting, updating and removing data from the database]].
 +
* [[Selecting data using JDatabase|Selecting data from one or more tables]] and retrieving it in a variety of different forms. Note: If you are looking for practical information about accessing the database in the old 1.5 document, you need to look at this part of the tutorial.
  
==Why should I use the Joomla database class?==
+
==Advanced information==
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.
+
This tutorial looks at how to use transactions with JDatabase (available since {{JVer|3.x}} only):
 +
* [[Using transactions in Joomla]]
  
==Preparing the query==
+
==Supported Storage Connectors==
<source lang="php">
+
The table below outlines the database and storage connectors available for Joomla! as well as which version of Joomla they became available in.
// Get a database object
+
$db =& JFactory::getDBO();
+
  
$query = "SELECT * FROM #__example_table WHERE id = 999999;";
+
To make a connector available in Joomla's installer or global configuration manager, you will need to ensure the PHP library is installed (E.g. for PHP5 and MySQL the php5-mysql library would need to be installed).
$db->setQuery($query);
+
</source>
+
  
First we instantiate the database object; then we prepare the query. You can use the normal SQL syntax. The only thing you have to change is the table prefix. To make this as flexible as possible, Joomla uses a placeholder for the prefix, the &ldquo;#__&rdquo;. In the next step, the $db->setQuery(), this string is replaced with the correct prefix.
+
{| class="wikitable"
 
+
! scope="col" | Database
Now, if we don't want to get information from the database, but rather insert a row into it, we need one more function. Every string value in the SQL syntax should be quoted. For example, MySQL uses backticks &#096;&#096; for names and single quotes &lsquo;&lsquo; for values. Joomla has some functions to do this for us and to ensure code compatibility between different databases. We can pass the names to the function $db->nameQuote($name) and the values to the function $db->Quote($value).
+
! scope="col" | Joomla Versions
 
+
! scope="col" | Joomla DB
A fully quoted query example is:
+
<source lang="php">
+
$query = "
+
  SELECT *
+
    FROM ".$db->nameQuote('#__example_table')." 
+
    WHERE ".$db->nameQuote('id')." = ".$db->quote('999999').";
+
  ";
+
</source>
+
 
+
Whatever we want to do, we have to set the query with the $db->setQuery() function. Although you could write the query directly as a parameter for $db->setQuery(), it's commonly done by first saving it in a variable, normally $query, and then handing this variable over. This results in clean, readable code.
+
 
+
==== setQuery($query) ====
+
The ''setQuery($query)'' method sets up a database query for later execution either by the query() method or one of the Load result methods.
+
<source lang="php">
+
$db =& JFactory::getDBO();
+
$query = "/* some valid sql string */";
+
$db->setQuery($query);
+
</source>
+
 
+
Notes:
+
The parameter $query must be a valid SQL string. It can either be added as a string parameter or as a variable. Generally a variable is preferred; it leads to more legible code and can help in debugging.
+
 
+
setQuery() also takes three other parameters: $offset, $limit (both used in list pagination) and $prefix, an alternative table prefix. All three variables have default values set and can usually be ignored.
+
 
+
==Executing the Query==
+
To execute the query, Joomla provides several functions, which differ in their return value.
+
 
+
=== Basic Query Execution ===
+
==== query() ====
+
The ''query()'' method is the the basic tool for executing SQL queries on a database. In Joomla it is most often used for updating or administering the database simply because the various load methods detailed on this page have the query step built into them.
+
 
+
The syntax is very straightforward:<source lang="php">$db =& JFactory::getDBO();
+
$query = "/* some valid sql string */";
+
$db->setQuery($query);
+
$result = $db->query();</source>
+
 
+
Note: $query() returns an appropriate database resource if successful, or FALSE if not.
+
 
+
=== Query Execution Information ===
+
* getAffectedRows()
+
* explain()
+
* insertid()
+
 
+
=== Insert Query Execution ===
+
* insertObject()
+
 
+
==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.
+
 
+
{| class="wikitable" style="text-align:center"
+
 
|-
 
|-
! id !! name !! email !! username
+
| MySQL || {{JVer|1.5}}{{JVer|2.5}}{{JVer|3.0}} || Yes
|-
+
| 1 || style="background:yellow" | John Smith || johnsmith@example.com || johnsmith
+
 
|-
 
|-
| 2 || Magda Hellman || magda_h@example.com || magdah
+
| Microsoft SQL Server || {{JVer|2.5}}{{JVer|3.0}} || Yes
 
|-
 
|-
| 3 || Yvonne de Gaulle || ydg@example.com || ydegaulle
+
| Microsoft SQL Azure || {{JVer|2.5}}{{JVer|3.0}} || Yes
|}
+
 
+
This is often the result of a 'count' query to get a number of records:
+
<source lang='php'>
+
$db =& JFactory::getDBO();
+
$query = "
+
  SELECT COUNT(*)
+
    FROM ".$db->nameQuote('#__my_table')."
+
    WHERE ".$db->nameQuote('name')." = ".$db->quote($value).";
+
  ";
+
$db->setQuery($query);
+
$count = $db->loadResult();
+
</source>
+
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).
+
<source lang='php'>
+
$db =& JFactory::getDBO();
+
$query = "
+
  SELECT ".$db->nameQuote('field_name')."
+
    FROM ".$db->nameQuote('#__my_table')."
+
    WHERE ".$db->nameQuote('some_name')." = ".$db->quote($some_value).";
+
  ";
+
$db->setQuery($query);
+
$result = $db->loadResult();
+
</source>
+
 
+
===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.
+
{| class="wikitable" style="text-align:center"
+
 
|-
 
|-
! id !! name !! email !! username
+
| Postgresql || {{JVer|3.0}} || Yes
|- style="background:yellow"
+
| 1 || John Smith || johnsmith@example.com || johnsmith
+
 
|-
 
|-
| 2 || Magda Hellman || magda_h@example.com || magdah
+
| Oracle DB || {{JVer|3.0}} || No
 
|-
 
|-
| 3 || Yvonne de Gaulle || ydg@example.com || ydegaulle
+
| SQL Lite || {{JVer|3.0}} || No
|}
+
 
+
==== loadRow() ====
+
loadRow() returns an indexed array from a single record in the table:
+
<source lang='php'>
+
. . .
+
$db->setQuery($query);
+
$row = $db->loadRow();
+
print_r($row);
+
</source>
+
will give:
+
<pre>Array ( [0] => 1 [1] => John Smith [2] => johnsmith@example.com [3] => johnsmith ) </pre>
+
 
+
You can access the individual values by using:<pre>$row['index'] // e.g. $row['2']</pre>
+
 
+
Notes:
+
# The array indices are numeric starting from zero.
+
# 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:
+
<source lang='php'>
+
. . .
+
$db->setQuery($query);
+
$row = $db->loadAssoc();
+
print_r($row);
+
</source>
+
will give:
+
<pre>Array ( [id] => 1 [name] => John Smith [email] => johnsmith@example.com [username] => johnsmith )</pre>
+
 
+
You can access the individual values by using:<pre>$row['name'] // e.g. $row['name']</pre>
+
 
+
Notes:
+
# 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:
+
<source lang='php'>
+
. . .
+
$db->setQuery($query);
+
$result = $db->loadObject();
+
print_r($result);
+
</source>
+
will give:
+
<pre>stdClass Object ( [id] => 1 [name] => John Smith [email] => johnsmith@example.com [username] => johnsmith )</pre>
+
 
+
You can access the individual values by using:<pre>$result->index // e.g. $result->email</pre>
+
 
+
Notes:
+
# 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.
+
 
+
{| class="wikitable" style="text-align:center"
+
 
|-
 
|-
! id !! name !! email !! username
+
| PHP Data Objects (PDO)* || {{JVer|3.0}} || No
|-
+
| 1 || style="background:yellow" | John Smith || johnsmith@example.com || johnsmith
+
|-
+
| 2 || style="background:yellow" | Magda Hellman || magda_h@example.com || magdah
+
|-
+
| 3 || style="background:yellow" | Yvonne de Gaulle || ydg@example.com || ydegaulle
+
 
|}
 
|}
  
==== loadResultArray() ====
+
* PHP Data Objects is a database abstraction layer and is shipped with PHP 5.1+.
loadResultArray() returns an indexed array from a single column in the table:
+
<source lang='php'>
+
$query = "
+
  SELECT name, email, username
+
    FROM . . . ";
+
. . .
+
$db->setQuery($query);
+
$column= $db->loadResultArray();
+
print_r($column);
+
</source>
+
will give:
+
<pre>Array ( [0] => John Smith [1] => Magda Hellman [2] => Yvonne de Gaulle )</pre>
+
 
+
You can access the individual values by using:<pre>$column['index'] // e.g. $column['2']</pre>
+
 
+
Notes:
+
# The array indices are numeric starting from zero.
+
# loadResultArray() is equivalent to loadResultArray(0).
+
 
+
==== loadResultArray($index) ====
+
loadResultArray($index) returns an indexed array from a single column in the table:
+
<source lang='php'>
+
$query = "
+
  SELECT name, email, username
+
    FROM . . . ";
+
. . .
+
$db->setQuery($query);
+
$column= $db->loadResultArray(1);
+
print_r($column);
+
</source>
+
will give:
+
<pre>Array ( [0] => johnsmith@example.com [1] => magda_h@example.com [2] => ydg@example.com )</pre>
+
 
+
You can access the individual values by using:<pre>$column['index'] // e.g. $column['2']</pre>
+
 
+
loadResultArray($index) allows you to iterate through a series of columns in the results
+
<source lang='php'>
+
. . .
+
$db->setQuery($query);
+
for ( $i = 0; $i <= 2; $i++ ) {
+
  $column= $db->loadResultArray($i);
+
  print_r($column);
+
}
+
</source>
+
will give:
+
<pre>Array ( [0] => John Smith [1] => Magda Hellman [2] => Yvonne de Gaulle )
+
Array ( [0] => johnsmith@example.com [1] => magda_h@example.com [2] => ydg@example.com )
+
Array ( [0] => johnsmith [1] => magdah [2] => ydegaulle )</pre>
+
</pre>
+
 
+
Notes:
+
# The array indices are numeric starting from zero.
+
 
+
=== Multi-Row Results ===
+
Each of these results functions will return multiple records from the database.
+
 
+
{| class="wikitable" style="text-align:center"
+
|-
+
! id !! name !! email !! username
+
|- style="background:yellow"
+
| 1 || John Smith || johnsmith@example.com || johnsmith
+
|- style="background:yellow"
+
| 2 || Magda Hellman || magda_h@example.com || magdah
+
|- style="background:yellow"
+
| 3 || Yvonne de Gaulle || ydg@example.com || ydegaulle
+
|}
+
 
+
==== loadRowList() ====
+
loadRowList() returns an indexed array of indexed arrays from the table records returned by the query:
+
<source lang='php'>
+
. . .
+
$db->setQuery($query);
+
$row = $db->loadRowList();
+
print_r($row);
+
</source>
+
will give (with line breaks added for clarity):
+
<pre>Array (
+
[0] => Array ( [0] => 1 [1] => John Smith [2] => johnsmith@example.com [3] => johnsmith )
+
[1] => Array ( [0] => 2 [1] => Magda Hellman [2] => magda_h@example.com [3] => magdah )
+
[2] => Array ( [0] => 3 [1] => Yvonne de Gaulle [2] => ydg@example.com [3] => ydegaulle )
+
)</pre>
+
 
+
You can access the individual rows by using:<pre>$row['index'] // e.g. $row['2']</pre>
+
and you can access the individual values by using:<pre>$row['index']['index'] // e.g. $row['2']['3']</pre>
+
 
+
Notes:
+
# 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:
+
<source lang='php'>
+
. . .
+
$db->setQuery($query);
+
$row = $db->loadAssocList();
+
print_r($row);
+
</source>
+
will give (with line breaks added for clarity):
+
<pre>Array (
+
[0] => Array ( [id] => 1 [name] => John Smith [email] => johnsmith@example.com [username] => johnsmith )
+
[1] => Array ( [id] => 2 [name] => Magda Hellman [email] => magda_h@example.com [username] => magdah )
+
[2] => Array ( [id] => 3 [name] => Yvonne de Gaulle [email] => ydg@example.com [username] => ydegaulle )
+
) </pre>
+
 
+
You can access the individual rows by using:<pre>$row['index'] // e.g. $row['2']</pre>
+
and you can access the individual values by using:<pre>$row['index']['column_name'] // e.g. $row['2']['email']</pre>
+
 
+
==== loadAssocList($key) ====
+
loadAssocList('key') returns an associated array - indexed on 'key' - of associated arrays from the table records returned by the query:
+
<source lang='php'>
+
. . .
+
$db->setQuery($query);
+
$row = $db->loadAssocList('username');
+
print_r($row);
+
</source>
+
will give (with line breaks added for clarity):
+
<pre>Array (
+
[johnsmith] => Array ( [id] => 1 [name] => John Smith [email] => johnsmith@example.com [username] => johnsmith )
+
[magdah] => Array ( [id] => 2 [name] => Magda Hellman [email] => magda_h@example.com [username] => magdah )
+
[ydegaulle] => Array ( [id] => 3 [name] => Yvonne de Gaulle [email] => ydg@example.com [username] => ydegaulle )
+
)</pre>
+
 
+
You can access the individual rows by using:<pre>$row['key_value'] // e.g. $row['johnsmith']</pre>
+
and you can access the individual values by using:<pre>$row['key_value']['column_name'] // e.g. $row['johnsmith']['email']</pre>
+
 
+
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:
+
<source lang='php'>
+
. . .
+
$db->setQuery($query);
+
$row = $db->loadObjectList();
+
print_r($row);
+
</source>
+
will give (with line breaks added for clarity):
+
<pre>Array (
+
[0] => stdClass Object ( [id] => 1 [name] => John Smith
+
    [email] => johnsmith@example.com [username] => johnsmith )
+
[1] => stdClass Object ( [id] => 2 [name] => Magda Hellman
+
    [email] => magda_h@example.com [username] => magdah )
+
[2] => stdClass Object ( [id] => 3 [name] => Yvonne de Gaulle
+
    [email] => ydg@example.com [username] => ydegaulle )
+
)</pre>
+
 
+
You can access the individual rows by using:<pre>$row['index'] // e.g. $row['2']</pre>
+
and you can access the individual values by using:<pre>$row['index']->name // e.g. $row['2']->email</pre>
+
 
+
==== loadObjectList('key') ====
+
loadObjectList($key) returns an associated array - indexed on 'key' - of objects from the table records returned by the query:
+
<source lang='php'>
+
. . .
+
$db->setQuery($query);
+
$row = $db->loadObjectList('username');
+
print_r($row);
+
</source>
+
will give (with line breaks added for clarity):
+
<pre>Array (
+
[johnsmith] => stdClass Object ( [id] => 1 [name] => John Smith
+
    [email] => johnsmith@example.com [username] => johnsmith )
+
[magdah] => stdClass Object ( [id] => 2 [name] => Magda Hellman
+
    [email] => magda_h@example.com [username] => magdah )
+
[ydegaulle] => stdClass Object ( [id] => 3 [name] => Yvonne de Gaulle
+
    [email] => ydg@example.com [username] => ydegaulle )
+
)</pre>
+
 
+
You can access the individual rows by using:<pre>$row['key_value'] // e.g. $row['johnsmith']</pre>
+
and you can access the individual values by using:<pre>$row['key_value']->column_name // e.g. $row['johnsmith']->email</pre>
+
 
+
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 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. 
+
<source lang='php'>
+
. . .
+
$db->setQuery($query);
+
$db->query();
+
$num_rows = $db->getNumRows();
+
print_r($num_rows);
+
$result = $db->loadRowList();
+
</source>
+
will return <pre>3</pre>
+
Note: if you run getNumRows() after loadRowList() - or any other retrieval method - you may get a PHP Warning:
+
<pre>Warning: mysql_num_rows(): 80 is not a valid MySQL result resource
+
in D:\xampp\htdocs\joomla1.5a\libraries\joomla\database\database\mysql.php on line 344</pre>
+
 
+
==Tips, Tricks & FAQ==
+
===Subqueries===
+
Subqueries should be written as follows:
+
<source lang="SQL">
+
SELECT * FROM #__example WHERE id IN (SELECT id FROM #__example2);
+
</source>
+
These kinds of queries are supported since MySQL 4.1. If this method fails, you can split the query into two as demonstrated below. Please note that this will (often unnecessarily) increase the load on the database server.
+
<source lang="php">
+
$query = "SELECT id FROM #__example2";
+
$database->setQuery($query);
+
$query = "SELECT * FROM #__example WHERE id IN (". implode(",", $database->loadResultArray()) .")";
+
</source>
+
 
+
===Developer-Friendly Tips===
+
Here is a quick way to do four developer-friendly things at once:
+
* Use a simple constant as an SQL seperator (which can probably be used in many queries).
+
* Make your SQL-in-PHP code easy to read (for yourself and possibly other developers later on).
+
* Give an error inside your (component-) content without really setting debugging on.
+
* Have a visibly nice SQL by splitting SQL groups with linebreaks in your error.
+
<source lang="php">
+
$db =& JFactory::getDBO();
+
$jAp=& JFactory::getApplication();
+
    //We define a linebreak constant
+
define('L', chr(10));
+
    //Here is the most magic
+
$db->setQuery(
+
'SELECT * FROM #__table'.L.
+
'WHERE something="something else")'.L.
+
'ORDER BY date desc'
+
);
+
$db->query();
+
    //display and convert to HTML when SQL error
+
if (is_null($posts=$db->loadRowList())) {$jAp->enqueueMessage(nl2br($db->getErrorMsg()),'error'); return;}
+
</source>
+
<noinclude>[[Category:Tutorials]][[Category:Development]][[Category:Database]]</noinclude>
+

Revision as of 18:06, 30 October 2013

Useful information

Being able to use JDatabase is vital when you start developing for Joomla. The tutorial is split into two independent parts:

Advanced information

This tutorial looks at how to use transactions with JDatabase (available since Joomla 3.x only):

Supported Storage Connectors

The table below outlines the database and storage connectors available for Joomla! as well as which version of Joomla they became available in.

To make a connector available in Joomla's installer or global configuration manager, you will need to ensure the PHP library is installed (E.g. for PHP5 and MySQL the php5-mysql library would need to be installed).

Database Joomla Versions Joomla DB
MySQL Joomla 1.5Joomla 2.5Joomla 3.0 Yes
Microsoft SQL Server Joomla 2.5Joomla 3.0 Yes
Microsoft SQL Azure Joomla 2.5Joomla 3.0 Yes
Postgresql Joomla 3.0 Yes
Oracle DB Joomla 3.0 No
SQL Lite Joomla 3.0 No
PHP Data Objects (PDO)* Joomla 3.0 No
  • PHP Data Objects is a database abstraction layer and is shipped with PHP 5.1+.