2010/7/31 Nicolás Sanguinetti <h...@nicolassanguinetti.info>:
> On Sat, Jul 31, 2010 at 6:08 PM, DBA <diogo.borges.alme...@gmail.com> wrote:
>> I've implemented the following scope in a rails 3 application:
>>
>> scope :popular, lambda { |l = 5| order('views desc').limit(l) }
>>
>> However, it seems that when you attempt to count its records directly
>> it doesn't apply the scope filters.
>>
>> For example:
>>
>> Post.popular.size #=> 20
>>
>> Checking the log, it executes the following query:
>>
>> SQL (0.4ms) SELECT COUNT(*) AS count_id FROM `posts` LIMIT 5
>>
>> Now if I execute
>>
>> Post.popular.all.size #=> 5
>>
>> And the correct query is executed:
>>
>> Post Load (1.5ms) SELECT `posts`.* FROM `posts` ORDER BY views
>> desc LIMIT 5
>>
>> Anyone else experienced this kind of behavior? If so, any idea if this
>> is the expected behavior or am I facing a bug?
>
> This is expected. The three ways to get the size of an ActiveRecord
> collection are:
>
> .count #=> this always triggers a SELECT COUNT(*) on the database
> .size #=> if the collection has been loaded, defers to
> Enumerable#size, else does the SELECT COUNT(*)
> .length #=> always loads the collection and then defers to
> Enumerable#size (I think it's length, but I don't think I ever used it
> :P)
>
> So, since Post.popular doesn't trigger the query and load the objects,
> calling size will do a count query.
>
> This is, apparently, a good use case for Post.popular.length :)
Or a good reason to change the code to do:
SELECT COUNT(*) FROM (SELECT `posts`.* FROM `posts` ORDER BY views
desc LIMIT 5) AS some_alias
which is Sequel's behavior.
Jeremy
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