Magento - Most efficient method of getting a collection count

Question

I have a helper method in Magento which requires me to get the count of several unrelated collections. Further to this, i need this information for each product in a category i.e. for each product in the product list view. So i will potentially be creating lots of collections repeatedly during the product list rendering.

What is the most efficient method of getting the count of a collection, that is, i do not need any data from the models, simply how many models there are.

Is it simply:

Mage::getResourceModel('mymodule/mymodel_collection')->addFilter('myattribute', $value)->count()

Or is there a more efficient way to do this?

Answer 1

For counting items in a collection, use the getSize() method:

$collection->getSize();

Never use the php count() function or the count() method of the collection like this:

count($collection)
$collection->count()

When you use the count() function/method, Magento loads all the items of the collection from the database. On large collections you will have an huge memory usage and possibly issues like Fatal error: Allowed memory size of 268435456 bytes exhausted (tried to allocate 71 bytes)...

Answer 2

Try as:

$collection = Mage::getResourceModel('mymodule/mymodel_collection')->addFieldFilter('myattribute', $value);
$collection->count();
//or
$collection->getSize();