Laravel development: How to implement polymorphic associations using Laravel Eloquent?

Laravel Development: How to use Laravel Eloquent to implement polymorphic associations?

Polymorphic association is an important feature of Laravel Eloquent, which allows one model to establish relationships with multiple different models. In practical applications, processing different types of data is relatively simple and efficient, especially in database design. In this article, we will discuss how to implement polymorphic associations using Laravel Eloquent.

1. What is polymorphic association?

Polymorphic association refers to the establishment of an association relationship between a model and multiple different models, which can be regarded as a reference to a general category. It can bring convenience to many applications, such as:

1. Image, audio and video models can all establish polymorphic associations with comment models, so that comments can be applied to multiple data types.
2. Users can establish polymorphic associations with comment models and be applied to a variety of data types, such as articles, pictures, videos, etc.
3. The order model can establish a polymorphic association with the delivery address model, so that orders can be delivered to multiple address types, such as homes, companies, outlets, etc.

2. Methods to implement polymorphic association

Let’s take a look at how to use Laravel Eloquent to implement polymorphic association.

First of all, we need to consider the design of the data table. We need to create an intermediate table to store polymorphic relationships between models. This table should contain the following columns:

1. id: table primary key ID;
2. target_type: type name of the target model;
3. target_id: ID of the target model;
4. source_type: The type name of the source model;
5. source_id: The ID of the source model.

The following is an example of a database migration file:

<?php

use IlluminateDatabaseMigrationsMigration;
use IlluminateDatabaseSchemaBlueprint;
use IlluminateSupportFacadesSchema;

class CreateCommentsTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('comments', function (Blueprint $table) {
            $table->id();
            $table->morphs('commentable');
            $table->text('content');
            $table->timestamps();
        });

        Schema::create('votes', function (Blueprint $table) {
            $table->id();
            $table->unsignedBigInteger('user_id');
            $table->unsignedBigInteger('voteable_id');
            $table->string('voteable_type');
            $table->enum('type', ['up', 'down']);
            $table->timestamps();
        });
    }

    /**
     * Reverse the migrations.
     *
     * @return void
     */
    public function down()
    {
        Schema::dropIfExists('comments');
        Schema::dropIfExists('votes');
    }
}

In the above migration file, we created two new tables: comments and votes.

The comments table contains basic information about the comment model, and uses the morphs() method to implement polymorphic association pointing. The votes table is similar, using voteable_id and voteable_type fields to implement polymorphic association.

Next, we need to define the association relationship in the Eloquent model.

Comment model:

<?php

namespace AppModels;

use IlluminateDatabaseEloquentFactoriesHasFactory;
use IlluminateDatabaseEloquentModel;

class Comment extends Model
{
    use HasFactory;

    public function commentable()
    {
        return $this->morphTo();
    }

    public function votes()
    {
        return $this->morphMany(Vote::class, 'voteable');
    }
}

Vote model:

<?php

namespace AppModels;

use IlluminateDatabaseEloquentFactoriesHasFactory;
use IlluminateDatabaseEloquentModel;

class Vote extends Model
{
    use HasFactory;

    public function voteable()
    {
        return $this->morphTo();
    }

    public function user()
    {
        return $this->belongsTo(User::class);
    }
}

The above code will define polymorphic relationships for the Comment model and the Vote model respectively. In the Comment model, we use the morphTo() method to define the polymorphic association to the comment, and in the Vote model, we use the morphMany() method to define the polymorphic association to the comment.

3. Use polymorphic association

Let us see how to use polymorphic association.

Create a comment:

$article = Article::find(1);

$comment = $article->comments()->create([
    'content' => 'This is a comment',
]);

Get votes for comments:

$votes = $comment->votes;

Get comments for articles:

$comments = $article->comments;

Votes:

$comment->votes()->create([
    'user_id' => 1,
    'type' => 'up',
]);

Above The code example demonstrates the basic use of polymorphic relationships, and you can find more details about this feature in the Laravel Eloquent documentation.

Summary

Polymorphic association is one of the important features of Laravel Eloquent, which allows one model to establish relationships with multiple different models. Very useful in database design and application development. When using Laravel Eloquent to implement polymorphic relationships, you need to design the intermediate table of the relationship and define the relationship in the Eloquent model. We can use the morphTo() and morphMany() methods to implement polymorphic relationships.

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