Nested Laravel Relationships

The code snippet below is part of a Laravel model called Message in one of my personal projects. To grasp its significance, I'll provide some necessary context without delving into the entire application's functionality.

Within the Message model, there's a method named message_data. For those unfamiliar with it, message_data is used for lazy loading. To appreciate the brilliance of this code, it's essential to understand lazy loading, but I'll keep it brief for now.

This method facilitates retrieving message_data by employing the with method on the model. This automates the extraction of data from another table linked through a foreign key.

public function message_data()
{
    return $this->belongsTo(
        $this->hasOne(MessageType::class, "id", "message_type_id")->first()->data_model,
        "messageable_id",
        "id"
    );
}
php

If this still seems a bit unclear, let me elaborate further on the Message model. In my project, a message can be either an email or an SMS, establishing a polymorphic relationship. To achieve this, I include a field to hold the polymorphic table's ID, typically suffixed with able to signal Laravel's understanding of its role in polymorphism.

The second part involves a field indicating the model, conventionally named with the _type suffix. However, I've opted for clarity, labeling it data_model.

Here's an example value:

App\Models\Email
php

which references the email model within the project.

Initially, I could have utilized Laravel's basic polymorphic approach to fetch message_data. However, due to project requirements—specifically, allowing users to switch between SMS and email types of messages—I needed a different approach.

Now, let's revisit the code snippet to understand its functionality.

The code first retrieves the current relationship table from the message_type table, which could be either SMS or email. After obtaining this information, it extracts the string value of the data model:

$this->hasOne(MessageType::class, "id", "message_type_id")->first()->data_model
php

This can result in \App\Models\Email. Using this dynamic model, it creates a belongsTo relationship within the Message model. Resulting in dynamic belongsTo relationship from a related table, allowing the user to switch from sms to email and vice versa.

The remarkable aspect lies in Laravel's ability to leverage one relationship functionality within another. It's truly impressive that you can nest relationships, enhancing the flexibility and power of the framework.