rails 4 scopes with NOT equal and associations

Question

I have a instance variable in my controller that I'm trying to convert into a scope for my model.

Instance variable: products

@products_with_user_differences = Product.where{|p| p.last_user != p.user.username && p.asset_type.name == "Computer" unless p.user.nil? or p.allow_multi_users == true}

Explanation:

This shows all Products that have a last_user value different from the user.username with a type of "Computer". It also excludes any Product that user_id: is nil or have allow_multi_users attribute set to TRUE.

I've tried the following with zero luck: Products.rb

scope :with_user_differences, -> { where(last_user != user.username && asset_type.name == "Computer" unless user.nil? or allow_multi_users == true)}

It doesn't seem to recognize associations or allow "!=" in the scope.

Any ideas or pointers?

In the first version you're using `where{` and in the second version `where(`. [A normal ActiveRecord `where`](http://guides.rubyonrails.org/active_record_querying.html#conditions) definitely can't do what you're trying to do in your scope. — Mischa, Apr 23 '14 at 02:04
thanks but i already realize that it can't do that because it doesn't work. any hints on the correct way to do it? — Devin, Apr 23 '14 at 02:14
Sorry if you think my comment wasn't helpful. I thought it'd help you realise *why* it doesn't work. I put a link in there that may be helpful when trying to rewrite your query. — Mischa, Apr 23 '14 at 02:46

jvnill · Answer 1 · 2014-04-23T08:07:22.043

The following code will return products that are associated to a user and an asset_type

Product.joins(:user, :asset_type)

To exclude products with allow_multi_users set to true

Product.where(allow_multi_users: false)

To get products where asset_type.name is computer, assuming you followed convention and asset_type is under a table called asset_types

# take note of the pluralized asset_type
Product.where(asset_types: { name: 'Computer' })

To get products where last_user is not equal to the associated user's username

Product.where('products.last_user != users.username')

Given all these, you can do the following

def self.with_user_differences
  Product
    .joins(:user, :asset_type)
    .where(assset_types: { name: 'Computer' })
    .where(allow_multi_users: false)
    .where('products.last_user != users.username')
end

You missed the `asset_type.name == "computer"` condition – Pavan Apr 23 '14 at 04:03 — Pavan, Apr 23 '14 at 04:03

rails 4 scopes with NOT equal and associations

1 Answers1