Failing validations in join model when using has_many :through

Question

My full code can be seen at https://github.com/andyw8/simpleform_examples

I have a join model ProductCategory with the following validations:

Answer 1

This is a "racing condition" in the callback chain.

When you create a product it doesn't have any id before it is saved, therefore there is no product in the scope of ProductCategory.

Product.new(name: "modern times", category_ids:[1, 2]) #=> #

At that stage of validation (before saving), ProductCatgory cannot assign any id to it's foreign key product_id.

That's the reason you have association validations : so that the validation happens in the scope of the whole transaction

UPDATE: As said in the comment you still can't ensure presence of a product/category. There's many ways around depending on why you want do this (e.g direct access to ProductCategory through some form)

• You can create a flag to have validates :product, presence: true, if: :direct_access?
• or if you can only update them: validates :product, presence: true, on: "update"
• create your product first (in the products_controller) and add the categories after

... But indeed these are all compromises or workarounds from the simple @product.create(params)