Question

Is it possible to make a query like this with rails?

SELECT items.*, (select count(*) from ads where item_id = items.id) as adscount WHERE 1

And then access this field like so?

@item.adscount 

For example for each item there is a hundred ads or so.
And in items index view I need to show how many ads each item has.

For now I only found out how to make a unique query for every item, for example:

select count(*) from ads where item_id = 1
select count(*) from ads where item_id = 2
select count(*) from ads where item_id = 3
etc

Edit:

Made a counter cache column.

That gave me huge performance improvement.

Answer 1

Use Rails Counter Cache http://railscasts.com/episodes/23-counter-cache-column

Then you will be able to use it like @item.ads.count and this will not produce any database queries.
And in addition (if you really want to use it your way) you can create a model method

def adscount
  self.ads.count
end