Polymorphic Associations in Ruby on Rails
In Ruby on Rails, associations allow us to establish relationships between models. One such association is polymorphic association, which provides a flexible way to connect multiple models to a single model. In this blog post, we will explore the concept of polymorphic associations in Ruby on Rails and how they can be utilized to build powerful and flexible relationships within your application.
Understanding Polymorphic Associations
Polymorphic associations enable a model to belong to more than one other model on a single association. This is particularly useful when you have multiple models that can be associated with a common model. For example, imagine a scenario where you have a Comment model and want to associate comments with various models like Article, Image, and Video. Polymorphic associations provide a clean solution for this kind of scenario.
Setting up Polymorphic Associations
To implement a polymorphic association, follow the steps below:
Step 1: Define the Polymorphic Association
To define a polymorphic association, you need to add two columns to the model that will have the polymorphic relationship. These columns will store the ID and type of the associated model. For example, let’s consider a Comment model that can belong to various models:
1 2 3 class Comment < ApplicationRecord belongs_to :commentable, polymorphic: true end
In this example, the
belongs_to association is defined with
commentable as the polymorphic association name.
Step 2: Define the Associated Models
Next, you need to define the associated models that can have a polymorphic relationship with the Comment model. For instance, let’s consider the Article and Image models:
1 2 3 4 5 6 7 class Article < ApplicationRecord has_many :comments, as: :commentable end class Image < ApplicationRecord has_many :comments, as: :commentable end
In both the Article and Image models, we define a
has_many association with
comments as the polymorphic association name.
Usage and Benefits of Polymorphic Associations
Once the polymorphic associations are set up, you can now take advantage of the flexibility they provide:
- Easy association creation: You can associate comments with any model that has a polymorphic association with the Comment model. For example, to associate a comment with an article:
1 2 article = Article.find(params[:article_id]) comment = article.comments.create(content: "Great article!")
- Simplified querying: You can easily retrieve associated comments for any model that has a polymorphic association. For example, to fetch comments for an image:
1 2 image = Image.find(params[:image_id]) comments = image.comments
- Code reusability: Polymorphic associations eliminate the need to create separate models for each type of association, promoting code reuse and maintainability.
- Flexibility in database schema: Polymorphic associations allow for flexible and dynamic relationships between models, as they are not bound to a fixed database schema.
Polymorphic associations in Ruby on Rails provide a flexible and efficient way to establish relationships between models.