unable to determine row count Ruby-On-Rails

im trying to build a cart in ruby on rails it requires me to show the output like this : You have 3 items in your cart (3 being the number of items in my cart) and im trying to find the number of rows in the table line_items where the cart_id is 5.

@line_items.find(:all, :condition => { :cart_id => "5"}).count

if anyone know how i 开发者_C百科should write this, please let me know.. Thanks in advance

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You can do it the slow way:

YourModelClass.find(:all, :conditions => { :card_id => 5 }).count

or the fast way:

YourModelClass.count(:conditions => { :card_id => 5 })

The fast way simply does a COUNT(*) inside the database, the slow way pulls the whole result set out of the database, turns it into objects, and then counts them.

There's also the modern Rails3+ way:

YourModelClass.where(:card_id => 5).count

That does a select count(*) from t where card_id = 5 inside the database. Don't use this one though:

YourModelClass.count(:card_id => 5)

That will do a select count(card_id = 5) from t and that's nothing at all like what you want.

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it should be something alone the line of

LineItem.count(:conditions => {:cart_id => 5})

since i don't really know what's the model name, and the association... hope this helps =)