Rails add reference

When building web applications, it is often necessary to associate records in different database tables. For example, a blog post might be associated with comments or authors.

In Rails, you can use the add_reference method to create a foreign key in a database table that references another table. This method generates a migration that adds a new column to the current table with a foreign key that references the primary key of the referenced table.

Syntax

The syntax for add_reference is as follows:

add_reference :table_name, :referenced_table_name, :options

• table_name: The name of the table to add the reference to.
• referenced_table_name: The name of the table to reference.
• options: A hash of options, such as null and index.

Example

If we want to associate blog posts with authors, we can create a foreign key from the posts table to the authors table using the add_reference method:

rails g migration AddAuthorToPosts author:references

This will generate the following migration:

class AddAuthorToPosts < ActiveRecord::Migration[6.1]
  def change
    add_reference :posts, :author, null: false, foreign_key: true
  end
end

This migration adds a new column author_id to the posts table that references the id column of the authors table. The null: false option specifies that the author_id column cannot be NULL, and the foreign_key: true option creates a foreign key constraint between the posts and authors tables.

Conclusion

The add_reference method is a simple and powerful way to add foreign keys to your Rails database tables. It makes it easy to associate records in your application and helps ensure data integrity.