What is Laravel Polymorphic Relationship?
Laravel Polymorphic Relationship is a feature that allows you to establish associations between different model types using a single association. In simpler terms, it enables a model to belong to multiple other models on a single association. This powerful concept eliminates the need for complex and redundant database structures, providing a more efficient and flexible way to handle relationships.
How Does Polymorphic Relationship Work?
Polymorphic relationships in Laravel are built on three key components: the polymorphic model, the polymorphic type, and the polymorphic ID.. The polymorphic model represents the model that can belong to multiple other models, while the polymorphic type and ID determine the specific relationship.
Let’s look at an example where a blog post can receive comments from both users and administrators to demonstrate this. To address both instances, we can utilise a single comments table with a polymorphic connection rather than making separate tables for user comments and admin comments. In the comments table, there would be columns for commentable_id, commentable_type, and content. Commentable_id would indicate the associated model’s ID, while commentable_type would indicate the type of model.
posts:
id
title
content
post_images:
id
url
image_type
post_id (foreign key referencing posts.id)
comments:
id
content
commentable_id
commentable_type
comment_images:
id
url
image_type
comment_id (foreign key referencing comments.id)Implementing Polymorphic Relationships
Implementing Laravel Polymorphic Relationships is a straight forward process. To establish a polymorphic relationship between two models, you need to define the relationship methods and set up the corresponding tables and columns.
Defining Polymorphic Relationships
In Laravel, you can define polymorphic relationships using the morphTo and morphMany methods.
MorphTo: This method is used on the model that can be associated with multiple other models. For example, a Comment model could be associated with either a Post model or an PostImage model. In this case, we would use the morphTo method on the Comment model, because the Comment model can be associated with multiple different types of models.
MorphMany: This method is used on the model that can have multiple associated models. For example, a Post model could have multiple comments associated with it. In this case, we would use the morphMany method on the Post model, because the Post model can have multiple associated Comment models.
Let’s go back to our earlier blog post with comments sample.. To set up the polymorphic relationship, we would define the following methods in our models:
class Comment extends Model
{
protected $fillable = ['content'];
public function commentable()
{
// This method returns the model that the comment is associated with.
return $this->morphTo();
}
}
class Post extends Model
{
public function comments()
{
// This method returns all of the comments associated with the post.
return $this->morphMany(Comment::class, 'commentable');
}
}The Comment model contains a commentable() method that establishes a polymorphic relationship using the morphTo() method. This allows the Comment model to be associated with various other models, such as Post and PostImage. The specific related model is determined by the commentable_type and commentable_id columns in the database table.
Creating the Database Structure
To support the polymorphic connection, we must add the required columns to the database table. The structure of the comments table in our example would be as follows:
Schema::create('comments', function (Blueprint $table) {
$table->id();
$table->unsignedBigInteger('commentable_id');
$table->string('commentable_type');
$table->text('content');
$table->timestamps();
});Handling Data with Polymorphic Relationships.
A few things to remember.
- To begin, ensure that the database table containing the polymorphic data has the right columns.
- The columns should indicate the model ID and the type of model with which the data is linked.
For example, if you have a polymorphic relationship between Comments and Posts, the database table would need to have columns for the commentable_id and commentable_type. - Second, you must ensure that you access the data using the proper techniques.
- To get all of the comments associated with a Post, for example, use the Post model’s comments() function.
For example, you cannot use polymorphic relationships to join tables together.
Retrieving Polymorphic Relationships
class Post extends Model
{
public function comments()
{
return $this->morphMany(Comment::class, 'commentable');
}
}
$post = Post::find(1);
$comments = $post->comments;class Comment extends Model
{
public function commentable()
{
return $this->morphTo();
}
}
$comment = Comment::find(1);
$commentable = $comment->commentable;Best Practices for Working with Polymorphic Relationships.
- Consistent Naming Conventions
- Proper Documentation and Comments.
- Testing and Validation.
If you have any question and any feedback, don’t hesitate in commenting below.
Everyone, have a great coding day!
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