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Home Backend Development PHP Tutorial Eloquent Multiple Associative Query Returns NULL Value Solution

Eloquent Multiple Associative Query Returns NULL Value Solution

Jul 23, 2025 pm 06:33 PM
laravel

Eloquent Multiple Associative Query Returns NULL Value Solution

This article aims to solve the problem that the associated data returns NULL value when using the with() method for multiple association queries. By analyzing model relationship definitions and query statements, a way to ensure that the associated data is properly obtained is provided, and sample code is included to help developers avoid similar errors.

In Laravel development, when using Eloquent ORM for database operations, you often encounter situations where you need to associate and query multiple tables. The with() method can easily implement preloading associated data, thereby avoiding N 1 query problems. However, sometimes when using the with() method for multiple association queries, the association data returns a NULL value, which is usually caused by not selecting the foreign key field required for the association relationship when querying.

To resolve this problem, the key is to make sure that the foreign key fields required for the association are selected in the main query. The following is an example showing how to use the with() method correctly for multiple association queries.

Suppose we have three models: Course, Files, and User. There is a belongsTo relationship between the Course model and the Files and User models. The Course model contains two foreign key fields, fileId and userId, which point to the id fields of the Files and User tables respectively.

Model definition:

 // Course Model
namespace App\Models;

use Illuminate\Database\Eloquent\Model;

class Course extends Model
{
    public function files()
    {
        return $this->belongsTo(Files::class, 'fileId', 'id');
    }

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

// Files Model
namespace App\Models;

use Illuminate\Database\Eloquent\Model;

class Files extends Model
{
    // ...
}

// User Model
namespace App\Models;

use Illuminate\Database\Eloquent\Model;

class User extends Model
{
    // ...
}

Error example:

The following code causes files and user relationships to return NULL values:

 $course = Course::with(['files:id,FileName,FilePath', 'user:id,name'])
    ->select('id', 'courseDisplayName', 'aboutCourse')
    ->where('userId', $request->tutorId)
    ->get();

Cause analysis:

In the above code, the select() method only selects the id, courseDisplayName, and aboutCourse fields, but does not select the two foreign key fields fileId and userId. Eloquent When loading an association, these foreign key fields are required to correctly associate the Course model with the Files and User models. Due to the lack of foreign key information, Eloquent cannot find the corresponding associated data, so it returns a NULL value.

Correct example:

The following code can correctly load the associated data:

 $course = Course::with(['files:id,FileName,FilePath', 'user:id,name'])
    ->select('id', 'courseDisplayName', 'aboutCourse', 'userId', 'fileId')
    ->where('userId', $request->tutorId)
    ->get();

Solution:

In the select() method, all foreign key fields required for the association must be selected. In this example, the userId and fileId fields need to be selected.

Summarize:

When using Eloquent's with() method for multiple association queries, be sure to make sure that all the foreign key fields required for the association are selected in the main query. This is the key to avoid the associated data returning NULL values. This problem can be effectively solved by carefully examining the query statement and model relationship definitions and ensuring that the associated data is properly obtained.

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