Ruby on Rails Explained
belongs_to

When developing a web application with Ruby on Rails, it is common to create associations between different models. Among the most important associations in Rails is the belongs_to method, which establishes a one-to-many relationship between two models.

What Does the belongs_to Method Do?

The belongs_to method is a Ruby on Rails method that defines a one-to-many relationship between two models. This method is used in the child model's class to specify its association with the parent model.

For instance, suppose we have two models, Author and Book, where each book belongs to an author. In that case, we can define the association in the Book model as follows:

class Book < ApplicationRecord
  belongs_to :author
end

This code specifies that each book belongs to an author, and that the author_id column should be used to establish the association.

How Does the belongs_to Method Work?

When using the belongs_to method, Rails creates an association between the child model and the parent model and adds a foreign key to the child model to reference the parent model. In the previous example, the Book model would have an author_id column that references the id column of the Author model.

We can use this association to access data from the parent model with ease. For example, if we have a book instance, we can access the author of the book using the following code:

book.author

This code will return the author of the book, as specified by the belongs_to association.

Options for the belongs_to Method

The belongs_to method accepts several options that can be used to customize the behavior of the association. Some of the most commonly used options include:

• class_name: Specifies the name of the associated class. For example, if the associated class is named Writer instead of Author, we can specify this using the class_name option:

class Book < ApplicationRecord
  belongs_to :writer, class_name: "Writer"
end

• foreign_key: Specifies the name of the foreign key column used to establish the association. For example, if we wanted to use a different column name than author_id, we could specify this using the foreign_key option:

class Book < ApplicationRecord
  belongs_to :author, foreign_key: "writer_id"
end

• optional: Specifies whether the association is optional or required. By default, the belongs_to association is required, meaning that the child model must have a valid parent model. If we want to allow the child model to exist without a parent model, we can specify this using the optional option:

class Book < ApplicationRecord
  belongs_to :author, optional: true
end

Conclusion

The belongs_to method is a powerful tool for establishing associations between models in Ruby on Rails. By using this method, we can effortlessly create one-to-many relationships between models, and access data from the parent model with ease. By understanding the options available for the belongs_to method, we can customize the behavior of our associations to fit our specific needs.