Methods and Products

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User Methods

You saw how to set up code to create likes, now it's time to improve the code with some additional methods.

like

To make things simpler, create a method in User for liking products.

Model Code

Here's one way you could create the method in User:

def like(product)
  Like.create(user_id: self.id, product_id:product.id)
end

Rails also lets you mention the model directly instead of the ID, so you can shorten the code:

def like(product)
  Like.create(user: self, product: product)
end

likes?

Add another method to user that checks if a user likes a specific product. To do this, check if the user's liked_products includes a given product.
(To find a method that check if an item exists in a collection, see Ruby Arrays or look at Ruby's enumerable docs.)

Model Code

Get the user's liked products and check if they include? the given product:

class User < ActiveRecord::Base
#...

  def likes?(product)
    liked_products.include?(product)
  end

end

(Note that liked_products is equivalent to self.liked_products, it returns all the liked_products of the user.)

validation

Can you add validations to the Like model to make sure every like has a user_id and product_id?

Model Code

validates :user_id, presence: true
validates :product_id, presence: true

dependent relationships

If you ever delete a user, their likes will still exist in the database.

table of likes 1

Above, user #1 is deleted, but now these 3 likes are all pointing to a user who does not exist:

table of likes 2

To fix this issue, add the dependent: :destroy option to the user-likes relationship:

user.rb

has_many :likes, dependent: :destroy

This will destroy all of a user's likes when the user is destroyed. So when user #1 gets deleted, his likes get deleted as well:

table of likes 3

Complete User Model

Here's how the User model should look:

models/user.rb

class User < ActiveRecord::Base

  # devise code...

  has_many :likes, dependent: :destroy
  has_many :products, through: :likes, source: :product

  def like(product)
     Like.create(user: self, product: product)
  end

  def likes?(product)
    liked_products.include?(product)
  end

end

Console Time

reload! your Rails console and try out your new user methods, for example:

p2 = Product.second 
u2 = User.second
u2.like(p2)
u2.likes?(p2)

Product's likes

You can now get all the products that a specific user likes. Can you add a line of code to the Product model to make it easy to get all the likes for a specific product?

Model Code

This is just a simple has_many line. If a product is destroyed, the likes are no longer relevant, so add the option to destroy them as well:

class Product < ActiveRecord::Base
  #..
  has_many :likes, dependent: :destroy
  #..
end

After adding the above code, you can now get the likes for a given product. reload! your rails console and try it out:

prod = Product.find 1
prod.likes

Liking Users

Optional Challenge

You can now get the likes for a given product, but what should you do if you wanted to get the actual users who like a product?

Guidelines

Add another relationship to the Product model.
Add a relationship to the Like model.

Model Code

Add the following code to the product model below has_many :likes, dependent: :destroy:

has_many :liking_users, through: :likes, source: :user

Then add the following code to the Like model:

 belongs_to :user

You can now reload your console and try getting liking_users for a given product!

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