Rails optional belongs_to

Question

I'm writing a Rails frontend for inventory management. I want users to be able to register products, so I have:

class User < ActiveRecord::Base   has_many :products   # <snip> end 

and

class Product < ActiveRecord::Base   belongs_to :user   # <snip> end 

The problem is that products are created prior to being registered by a user. That is, it's perfectly acceptable to call Product.create and just have it set the user_id to nil. As you can imagine, though, Rails doesn't support this out of the box:

> Product.create!    (0.3ms)  SELECT COUNT(*) FROM "products" WHERE "products"."type" IN ('Product')    (0.1ms)  begin transaction    (0.1ms)  rollback transaction ActiveRecord::RecordInvalid: Validation failed: User can't be blank     from ~/.rvm/gems/ruby-2.0.0-p0/gems/activerecord-3.2.13/lib/active_record/validations.rb:56:in `save!' 

I've thought about a bunch of kludgey workarounds, the most appealing of which is to have a NullUser subclassing User and use that to create products. But that still seems like a hack. What's the Rails Way with this?

Thanks.

---

The relevant migration:

class AddUseridToProducts < ActiveRecord::Migration   def change     add_column :products, :user_id, :integer   end end 

and later:

class Changeuseridtobeoptionalforproducts < ActiveRecord::Migration   def change     change_column :products, :user_id, :integer, null: true   end end 

Answer 1

Just an update for rails 5, if you want this kind of behavior you will need to pass this option:

belongs_to :user, optional: true 

In Rails 5, whenever we define a belongs_to association, it is required to have the associated record present by default.

Update
If you still want to use the old behavior by default you can add the configuration to your application.rb file.

# /config/application.rb config.active_record.belongs_to_required_by_default = false 

notice: there were some issues on early releases of Rails 5 with this configuration, but is currently fixed, tested on the release candidate 5.2.3.

Answer 2

Rails absolutely supports this out of the box, check your migrate, have you included a constraint such as :null => false on the user_id line? If so, take it out!

Edit: Or as @Rodrigo Dias states, reverse it to :null => true.

Also, check that you don't have any validations on the user relation in the Product model.