How to Use the Rails has_many Method

09/19/2021

Contents

In this article, you will learn how to use the Rails has_many method.

Rails has_many Method

The has_many method in Ruby on Rails is used to define a one-to-many association between two ActiveRecord models. Here’s how to use it:

First, you need to have two models that you want to associate with each other. Let’s say you have a User model and a Post model.

In your User model, you can define the association by adding the has_many method. For example:

class User < ApplicationRecord
  has_many :posts
end

This tells Rails that a user can have many posts.

In your Post model, you can define the inverse association by adding the belongs_to method. For example:

class Post < ApplicationRecord
  belongs_to :user
end

This tells Rails that a post belongs to a user.

With this association set up, you can now use the posts method on a User object to retrieve all of the posts associated with that user. For example:

user = User.find(1)
user.posts

This will return all of the posts associated with the user with ID 1.

You can also create a new post associated with a user by using the create method on the posts association. For example:

user = User.find(1)
user.posts.create(title: "My First Post", content: "Hello, world!")

This will create a new post with the given title and content, and associate it with the user with ID 1.

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