Why do I get an Unknown Primary Key exception for a join table in Rails 4?

Question

These are my models:

class Product
  has_many :line_items
  has_many :orders, :through => :line_items
end

class LineItem 
  belongs_to :order
  belongs_t         


        

Answer 1

In model add the following:

self.primary_key = [:order_id, :product_id]

and I think it would be wise to ensure that there's an index on those columns.

You may create one with following migration:

add_index :line_items, [:order_id, :product_id]