Eloquent eager loading, bug or intended behaviour?

[dododedodonl]

• Laravel Version: 7.16.1
• PHP Version: 7.4.3
• Database Driver & Version: mariadb 10.4.10

Description:

When using eager loading on a model, another query's output in the relationship method changes.

Steps To Reproduce:

Model relations:

User -- hasOne --> Merchant
Post -- hasMany --> Comment
Merchant -- belongsTo --> User
Comments-- belongsTo --> Post

Have the default user model with relationship merchant

<?php

namespace App;

use Illuminate\Foundation\Auth\User as Authenticatable;
use Illuminate\Notifications\Notifiable;

class User extends Authenticatable
{
    use Notifiable;

    public function merchant()
    {
        return $this->hasOne(\App\Merchant::class);
    }
}

Have a post model with an other relationship, depending on other data

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Post extends Model
{
    public function comments()
    {
        return $this->hasMany(\App\Comment::class)
            ->where('priviliged', auth()->user()->merchant->priviliged);
    }
}

When the comments are retrieved as Post::first()->comments, the code works as expected.
When the comments are retrieved as Post::with('comments')->first()->comments, the code does not work as expected.

I tried narrowing down the problem, and it looks like the nested query is the problem.
As a simplification I used this code.

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Post extends Model
{
    public function comments()
    {
        $user = User::find(3); // hard code user so this is no variable
        dump($user->merchant->id); // retrieve the id to verify which data is retrieved

        return $this->hasMany(\App\Comment::class)
            ->where('priviliged', auth()->user()->merchant->priviliged);
    }
}

When running Post::first()->comments, it dumps the correct merchant id (in this case 3).
The query executed for the User->merchant relationship is select * from merchants where merchants.user_id = ? and merchants.user_id is not null.

When running Post::with('comments')->first()->comments, it dumps a different merchant id (in this case 1). Upon further inspection, all merchants are retrieved, and the first merchant is selected.
The query exectued for the User->merchant relationship is select * from merchants.

I do not understand enough of the eager loading mechanism to determine if this is intended behaviour or a bug.

[staudenmeir]

What's the result of dump(auth()->user()->getAttributes(), auth()->user()->merchant->getAttributes()); in the last relationship?

[dododedodonl]

For Post::first()->comments the results of the 2 dumps (of seeded faker data) are:

array:9 [
  "id" => 3
  "name" => "Dr. Cortez Parker Jr."
  "email" => "[email protected]"
  "email_verified_at" => "2020-06-18 13:31:27"
  "password" => "$2y$10$92IXUNpkjO0rOQ5byMi.Ye4oKoEa3Ro9llC/.og/at2.uheWG/igi"
  "remember_token" => "3EFVcjXHtT"
  "created_at" => "2020-06-18 13:31:27"
  "updated_at" => "2020-06-18 13:31:27"
  "deleted_at" => null
]
array:6 [
  "id" => 3
  "user_id" => 3
  "name" => "Mr. Eduardo Goldner"
  "created_at" => "2020-06-18 13:31:27"
  "updated_at" => "2020-06-18 13:31:27"
  "deleted_at" => null
]

For Post::with('comments')->first()->comments the results of the 2 dumps are:

array:9 [
  "id" => 3
  "name" => "Dr. Cortez Parker Jr."
  "email" => "[email protected]"
  "email_verified_at" => "2020-06-18 13:31:27"
  "password" => "$2y$10$92IXUNpkjO0rOQ5byMi.Ye4oKoEa3Ro9llC/.og/at2.uheWG/igi"
  "remember_token" => "3EFVcjXHtT"
  "created_at" => "2020-06-18 13:31:27"
  "updated_at" => "2020-06-18 13:31:27"
  "deleted_at" => null
]
array:6 [
  "id" => 1
  "user_id" => 1
  "name" => "Miss Cassidy Christiansen Sr."
  "created_at" => "2020-06-18 13:31:27"
  "updated_at" => "2020-06-18 13:31:27"
  "deleted_at" => null
]

When I change the relationship from hasOne to hasMany, in the second case all merchants (existing in the database) are returned, while in the first case only the correct merchant is returned. Also, for the second case the where clause is not set on the querybuilder object, while it is set for the first case.

[staudenmeir]

Can you log all the executed queries for both lazy and eager loading?

[dododedodonl]

I used this comments function on the post model.

public function comments()
{
    $user = User::find(3); // hard code user so this is no variable
    dump($user->merchant->id); // retrieve the id to verify which data is retrieved

    dump(auth()->user()->getAttributes());
    dump(auth()->user()->merchant->getAttributes());

    return $this->hasMany(\App\Comment::class);
}

Running Post::first()->comments, the next queries are executed:

select * from `posts` limit 1   
select * from `users` where `users`.`id` = ? limit 1   
select * from `merchants` where `merchants`.`user_id` = ? and `merchants`.`user_id` is not null limit 1   
select * from `users` where `id` = ? limit 1   
select * from `merchants` where `merchants`.`user_id` = ? and `merchants`.`user_id` is not null limit 1   
select * from `comments` where `comments`.`post_id` = ? and `comments`.`post_id` is not null 

Running Post::with('comments')->first()->comments, the next queries are executed:

select * from `posts` limit 1   
select * from `users` where `users`.`id` = ? limit 1   
select * from `merchants` limit 1   
select * from `users` where `id` = ? limit 1   
select * from `merchants` limit 1   
select * from `comments` where `comments`.`post_id` in (1)  

[staudenmeir]

Please share the complete User, Post, Comment and Merchant models.

[dododedodonl]

Before posting anything here, I already dummed them down as far as I could and still had the same results. I used these models for testing.

User.php

<?php

namespace App;

use Illuminate\Foundation\Auth\User as Authenticatable;
use Illuminate\Notifications\Notifiable;

class User extends Authenticatable
{
    use Notifiable;

    public function merchant()
    {
        return $this->hasOne(\App\Merchant::class);
    }
}

Post.php

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Post extends Model
{
    public function comments()
    {
        $user = User::find(3);
        dump($user->merchant->id);

        dump(auth()->user()->getAttributes());
        dump(auth()->user()->merchant->getAttributes());

        return $this->hasMany(\App\Comment::class);
    }
}

Comment.php

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Comment extends Model
{
    public function post()
    {
        return $this->belongsTo(\App\Post::class);
    }
}

Merchant.php

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Merchant extends Model
{
    public function user()
    {
        return $this->belongsTo(\App\User::class);
    }
}

[staudenmeir]

Can you reproduce the issue on a fresh Laravel installation?

[dododedodonl]

Yes, that is what I did before posting here. The results are the same on a fresh laravel 7.16.1 install.

[staudenmeir]

Can you upload it to a GitHub repository?

[dododedodonl]

Just did that: https://github.com/dododedodonl/temp-elqouent-test

[staudenmeir]

The behavior is surprising, but I wouldn't consider it a bug. Relationships aren't meant to be built dynamically with additional queries.

Eager loading removes relationship constraints with Relation::noConstraints() and this also affects other queries that happen during this eager loading process.

Possible workarounds for your situation:

• Always load the merchant with the user:

class User extends Authenticatable
{
    protected $with = ['merchant'];
}

• Use eager loading for the merchant:

class Post extends Model
{
    public function comments()
    {
        return $this->hasMany(\App\Comment::class)
            ->where('priviliged', auth()->user()->load('merchant')->merchant->priviliged);
    }
}

[dododedodonl]

Okay, thank you for clarifying the process. Should this surprising behavior maybe be mentioned in the docs?