Laravel: Custom Foreign Key in One-To-Many Relationship Does Not Resolve

There are two Models User and Submission and a User can have any number of submissions in which he is referenced as Author. I have set up the relationship according to the documentation and the result of hasMany() is working fine. Only the belongsTo() method does not return the expected objects.

Here is the migration of my models:

Schema::create('users', function (Blueprint $table) {
    $table->id();
});

Schema::create('submissions', function (Blueprint $table) {
    $table->id();
    $table->foreignId( 'author' );
    $table->foreign( 'author' )->references('id')->on('users');
});

And these are the relationships within my models:

class User extends Authenticatable {
    public function submissions() {
        return $this->hasMany( 'App\Submission', 'author' );
    }
}

class Submission extends Model {
    public function author() {
        return $this->belongsTo( 'App\User', 'author' );
    }
}

Now, in my controller I want to execute this code:

$author = Submission::find(1)->author;
dd($author);

But, instead of the user object, the stored integer value of the author ID is printed. The relationship does not seem to be resolved via the author() method. On the other hand, when I fetch a user and their submissions, everything works as expected, i.e. the submissions are printed as objects:

$u = User::find(1)->submissions;
dd($u);

But the relation from Submission to User does get resolved properly, when I do not define a custom foreign key with belongsTo and rename the colum to author_id.

The configuration that works is this one:

//migration for Submissions table
Schema::create('submissions', function (Blueprint $table) {
    $table->id();
    $table->foreignId( 'author_id' );
    $table->foreign( 'author_id' )->references('id')->on('users');
});

//within Submission model
public function author() {
    return $this->belongsTo( 'App\User' );
}

I have the feeling that I'm missing something. Is there any additional link I have to make? I browsed through the documentation and the web for solutions, but to no success. If there is no other solution, I'll follow with renaming the column. But I'd rather understand the cause of my problem and work with my original design.

you should not name relation functions and fields using the same string.

When you have a column author and a public function author() laravel goes for column content first.

Add '_id' to the column, so you do not need to define referenced field in $this->belongsTo( 'App\User', 'author' );.