CODEWITHSUNDEEP
ruby-on-railsmodelhas-many
etlds
etlds

Reputation: 5890

ruby on rails manys' many

I am wondering how to do this without double each loop. Assume that I have a user model and order model, and user has_many orders.

Now I have a users array which class is User::ActiveRecord_Relation

How can I get the orders of these users in one line?

Upvotes: 0

Views: 34

Answers (3)

tadman
tadman

Reputation: 211540

If you've got a many-to-many association and you need to quickly load in all the associated orders you will need to be careful to avoid the so-called "N plus 1" load that can result from the most obvious approach:

orders = users.collect(&:orders).flatten

This will iterate over each user and run a query like SELECT * FROM orders WHERE user_id=? without any grouping.

What you really want is this:

orders = Order.where(user_id: users.collect(&:id))

That should find all orders from all users in a single query.

Upvotes: 1

Uelb
Uelb

Reputation: 4093

Actually, the best way to do that is : 

users.includes(:orders).map(&:orders)

Cause you eager load the orders of the users (only 2 sql queries)

Or 

Order.where(user_id: users.pluck(:id))

is quite good too in term of performance

Upvotes: 2

etlds
etlds

Reputation: 5890

An answer just come up my mind after I asked....

users.map {|user| user.orders}

Upvotes: 0

Related Questions