Interesting Things
- Given a list of IDs, how do you find which ones are not in the database?
ids = [1,2,3,4,5,0] missing_ids = ids - Model.find_all_by_id(ids).collect(&:id)
- Sarah Mei is hosting a Ruby Hack Night at pivotal labs tomorrow at 7PM (Tues April 27th. 731 Market St Floor 3, San Francisco).
- There is an android users group tomorrow. We don't know any more about it than that.
You don't want to instantiate those objects. Wow.
Use #select or use a method from ActiveRecord::ConnectionAdapters::DatabaseStatements.
ids = [1,2,3,4444444] missing_ids = ids - Model.select(:id).where(id: ids).all.map(&:id)
Yep, or pre r3:
I thought that exists? might work for this, but you'd have to iterative over ids, generating loads more queries than you need. You can pass it conditions, but it will return a simple 'true' if ANY of the records have that ID.
Regardless of WT or Sam's solution, you're still instantiating objects. Thanks for pointing out that we should only be brining back the IDs, however, that can be a big performance win. If you really only want the IDs and not objects, you'd have to write straight SQL (which isn't very rails friendly):
ids - Model.connection.select_values("SELECT
#{Model.primary_key}FROM#{Model.table_name}WHERE#{Model.primary_key}IN (#{ids.join(",")})").collect(&:to_i)The above statement doesn't use adapter-specific column or table name quoting, which would have made it even more generic for non-mysql adapters.
Also, it wasn't stated originally, but there was an object caching layer (via cache money I think) that direct SQL access would have bypassed.
You can pass it conditions, but it will return a simple 'true' if ANY of the records have that ID.
remove