db_fetch_array() vs. db_fetch_object()

Question

Drupal provides these two methods for iterating through a db_query() result. For example,

$users = array();
$result = db_query('SELECT uid FROM {users} WHERE status=0 AND login=0');
while ($row = db_fetch_object($result)) {
    $users[] = $row->uid;
}

However, it seems that db_fetch_array($result) could be used just the same here, only with $row['uid'] on the next line.

What is the difference between these two methods? Are they completely interchangeable?

Source: http://api.drupal.org/api/group/database/6

score 12 · Accepted Answer · 2010-08-17 23:46:28Z

12

The difference is that db_fetch_array() returns an array, whereas db_fetch_object() returns an object. Depending on the use-case, you might need one or the other.

It appears, at least given the snippet you provided, they are indeed—with a change in syntax like you mentioned—interchangeable for your use-case.

Edit

Drupal's db_fetch_object() and db_fetch_array() are inherited from PHP's *_fetch_object and *_fetch_array: Drupal merely abstracts PHP's database specific versions so a Drupal developer doesn't have to care what database is used in the backend.

So, the same reasons why they both exist in PHP are the same reasons why they exist in Drupal. They provide flexibility to developers: some use-cases require arrays, some require objects.

In Drupal core, db_fetch_object() is favored far more than db_fetch_array(): you can see how each are used within core by going to each function's API page and clicking on the header n functions call functionname.

The reason for this bias towards db_fetch_object is mainly preference and ease of maintenance: it's less characters to say $object->property than it is to say $object['property']. A lot of code style in Drupal is based on years of convention.

You can use either, but think whether it makes sense, semantically, for your data to be an object or an array. For example, if you wanted to take advantage of PHP's plethora of array functions (like array_merge(), which doesn't have a simple object analogue), you might opt to buck convention and use db_fetch_array().

All things being equal, *_fetch_object() is identical to *_fetch_array in terms of speed, but the resulting object from the former takes up slightly more memory than the resulting array from the latter.

edited Aug 17, 2010 at 23:46

answered Aug 17, 2010 at 20:42

user113292

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3 Comments

feedbackloop Over a year ago

1) Can you give an example where you'd use one rather than the other? 2) Is there a performance difference between the two?

user113292 Over a year ago

Sure; I've revised my answer to provide more background.

Angry Dan Over a year ago

Don't forget that objects are passed around by reference whereas arrays are passed by copy. This means that if another function modifies your object that reflects everywhere. This could be to your benefit or detriment depending on what your up to, but it's often a consideration. E.g. node_load uses db_fetch_object because node's are modified all over the place and saved at will.

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