In this blog post, we'll explore one to many associations in Rails, including how to set them up, how to use them in your applications, and examples of when they can be useful.
Setting up a One to Many Association
To set up a one to many association in Rails, you'll need to add a foreign key to the table that will have multiple records associated with a single record in the other table. For example, let's say we have two tables: Users and Posts. Each user can have many posts, but each post can only belong to one user.
To set up this association, we would add a user_id column to the Posts table, like so:
rails generate migration add_user_id_to_posts user:references
This will create a new migration that adds a user_id column to the Posts table and creates a foreign key reference to the Users table.
Next, we'll need to update our models to specify the association. In the User model, we'll add.
class User < ApplicationRecord
has_many :posts
end
And in the Post model, we'll add
class Post < ApplicationRecord
belongs_to :user
end
This sets up the one to many association between the User and Post models.
Using a One to Many Association
Now that we've set up our one to many association, we can use it in our applications. For example, if we wanted to display all of a user's posts on their profile page, we could do something like this:
class UsersController < ApplicationController
def show
@user = User.find(params[:id])
@posts = @user.posts
end
end
This will find the user with the given id, and then retrieve all of their associated posts using the @user.posts association.
Examples of When to Use a One to Many Association
One to many associations can be useful in many different scenarios. Here are a few examples:
- Blogging Platform
- E-commerce Platform
- Social Network
