Undefined property when belongs to fk name matches relation name

[matt-allan]

• Laravel Version: 6.10.1
• PHP Version: 7.3.13
• Database Driver & Version: Any

Description:

When the foreign key name for a belongsTo relation is the same as the relationship name, accessing the relationship method throws an undefined property error unless the field has previously been set (i.e. when fetching from the database).

Steps To Reproduce:

In a standard Laravel app add the following method to App\User:

    public function state()
    {
        return $this->BelongsTo(State::class, 'state');
    }

Open a tinker shell and attempt to access the state property or the state method

>>> (new App\User)->state
PHP Notice:  Undefined property: App/User::$state in /Users/matt/code/model-issue/vendor/laravel/framework/src/Illuminate/Database/Eloquent/Relations/BelongsTo.php on line 99
>>> (new App\User)->state()
PHP Notice:  Undefined property: App/User::$state in /Users/matt/code/model-issue/vendor/laravel/framework/src/Illuminate/Database/Eloquent/Relations/BelongsTo.php on line 99

Here's the stack trace:

1) Tests\Feature\ExampleTest::testBasicTest
ErrorException: Undefined property: App\User::$state

/Users/matt/code/model-issue/vendor/laravel/framework/src/Illuminate/Database/Eloquent/Relations/BelongsTo.php:99
/Users/matt/code/model-issue/vendor/laravel/framework/src/Illuminate/Database/Eloquent/Relations/Relation.php:71
/Users/matt/code/model-issue/vendor/laravel/framework/src/Illuminate/Database/Eloquent/Relations/BelongsTo.php:69
/Users/matt/code/model-issue/vendor/laravel/framework/src/Illuminate/Database/Eloquent/Concerns/HasRelationships.php:210
/Users/matt/code/model-issue/vendor/laravel/framework/src/Illuminate/Database/Eloquent/Concerns/HasRelationships.php:194
/Users/matt/code/model-issue/app/User.php:42
/Users/matt/code/model-issue/vendor/laravel/framework/src/Illuminate/Database/Eloquent/Concerns/HasAttributes.php:415
/Users/matt/code/model-issue/vendor/laravel/framework/src/Illuminate/Database/Eloquent/Concerns/HasAttributes.php:401
/Users/matt/code/model-issue/vendor/laravel/framework/src/Illuminate/Database/Eloquent/Concerns/HasAttributes.php:333
/Users/matt/code/model-issue/vendor/laravel/framework/src/Illuminate/Database/Eloquent/Model.php:1523
/Users/matt/code/model-issue/tests/Feature/ExampleTest.php:18

Expected output:

• Accessing the property returns null
• Accessing the method returns the BelongsTo relation

Note that the error does not occur if the property has been set, either manually or when fetching from the database.

I pushed a sample app with seeds, migrations, etc here.

[Miguel-Serejo]

I think this is a known limitation.

How would Eloquent know if $user->state should fetch the relationship or simply return the property?

[matt-allan]

Hi @36864, I didn't see any mentions of this in the docs or in existing issues so I opened an issue.

How would Eloquent know if $user->state should fetch the relationship or simply return the property?

In this example Eloquent is accessing the property itself and it knows it wants to fetch the property, not the relationship.

[Miguel-Serejo]

In this example Eloquent is accessing the property itself and it knows it wants to fetch the property, not the relationship.

But if in your code you try to access $user->state, are you trying to get the property or the relationship? How do you get the other? I think this was never made to work because that question was never answered unanimously.

Just use a different name for either the relation or the property.

[matt-allan]

But if in your code you try to access $user->state, are you trying to get the property or the relationship? How do you get the other?

In this case I would expect $user->state to return the string for the column. If I need to get the related model I can use $user->state()->first().

This is how it works currently if you fetch the model from the database or instantiate it with the property explicitly set.

>>> $user = App\User::first()
=> App\User {#3014
     id: 1,
     name: "fWHafxtduH",
     email: "[email protected]",
     email_verified_at: null,
     state: "FL",
     created_at: null,
     updated_at: null,
   }
>>> $user->state
=> "FL"
>>> $user->state()->first()
=> App\State {#3013
     id: "FL",
   }

If I could easily use a different property name I would but I'm working in an existing codebase with an existing database; refactoring everything is rather difficult at this point.

This issue doesn't seem too difficult to fix (i.e. calling $this->child->getAttributeValue($this->foreignKey) instead of $this->child->{$this->foreignKey} should work) and I think it's preferable that Eloquent doesn't throw an exception if it doesn't have to.

[Miguel-Serejo]

I am 0/2 today on this type of issue, sorry.

Traced the issue to

framework/src/Illuminate/Database/Eloquent/Concerns/HasAttributes.php

Lines 326 to 331 in 917ee51

	// Here we will determine if the model base class itself contains this given key
	// since we don't want to treat any of those methods as relationships because
	// they are all intended as helper methods and none of these are relations.
	if (method_exists(self::class, $key)) {
	return;
	}

This is called from the magic __get() method in the model, which is called when eloquent attempts to retrieve the property value.

This appears to be intentional, but maybe it can be changed?

[driesvints]

Hey @matt-allan, this is indeed not supported but you're right that the docs aren't clear on this. I also didn't find a note immediately. I've sent in a PR to clarify this at the top of the relationship docs. Thanks for reporting.

laravel/docs#5718