How to Retrieve Nested Data from Eloquent Models in Laravel: A Practical Guide

Laravel Nested Relationships: Unraveling Complex Data Retrieval

One of the strengths of Laravel lies in its ability to handle complex relationships between models. However, retrieving nested data can sometimes prove challenging. In this article, we'll address a common issue involving a deeply nested relationship and demonstrate how to achieve the desired result with Laravel's powerful ORM.

Suppose you have a scenario where you need to retrieve a list of persons who have subscribed to a specific event. The event, in turn, is linked to a city, while the city is associated with one or more companies. Finally, each company employs several persons.

To resolve this nested relationship, avoid using a raw SQL query as it can lead to performance penalties and maintenance challenges. Instead, let's leverage Laravel's eloquent relationships.

// Event Model
class Event extends Eloquent
{
    public function city()
    {
        return $this->belongsTo('City');
    }
}

// City Model
class City extends Eloquent
{
    public function companies()
    {
        return $this->hasMany('Company');
    }
}

// Company Model
class Company extends Eloquent
{
    public function persons()
    {
        return $this->hasMany('Person');
    }
}

// Person Model
class Person extends Eloquent
{
    public function company()
    {
        return $this->belongsTo('Company');
    }
}

The correct query to retrieve the desired nested data is:

Event::with('city.companies.persons')->get();

By utilizing the "with()" method, you can specify the related models you wish to retrieve along with the main model. In this case, we specify that we want to retrieve the "city" relation, followed by the "companies" relation, and finally the "persons" relation associated with each company.

The result of this query will be an Eloquent collection that contains Event models, each of which has access to its corresponding City, Companies, and Persons models.

// To retrieve specific fields from the persons table
Event::with(['city.companies.persons' => function ($query) {
    $query->select('id', '...');
}])->get();

By incorporating this technique into your Laravel application, you can simplify the retrieval of deeply nested data, ensuring maintainable and efficient code.

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