CODEWITHSUNDEEP
laravelmany-to-manyeloquentrelationships
Chris
Chris

Reputation: 4436

Use a different column on a many-to-many relationship in Laravel 4

I've got a situation in a project where I need to form a relationship between a primary key on one table and an indexed column (not the primary key) on another. Here's a sample of the database layout:

courses table
id
level

resources table
id

courses_resources table
course_level
resource_id

In my CourseResource model I have the following:

public function courses(){
    return $this->belongsToMany('Course', 'courses_resources', 'resource_id', 'course_level');
}

Which works fine.

Then in my Course model I have:

public function resources(){
    return $this->belongsToMany('CourseResource', 'course_resources', 'course_level', 'resource_id');
}

Which doesn't work. When I look at the last query performed on the database, it appears Laravel is searching the course_level column using the course's ID. That makes sense, but is there any way to use the level column for this relationship?

Upvotes: 0

Views: 132

Answers (1)

Jarek Tkaczyk
Jarek Tkaczyk

Reputation: 81157

Eloquent BelongsToMany depends on PKs, so there is no way to do that with its methods.

You need custom relation object for this, that will check for given field, instead of primary key.

A quick and hacky solution would be this:

// Course model
public function getKey()
{
    $relation = array_get(debug_backtrace(1, 2), '1.object', null);

    if (method_exists($relation, 'getForeignKey') 
          && $relation->getForeignKey() == 'courses_resources.course_level')
    {
        return $this->getAttribute('level');
    }

    return parent::getKey();
}

However if you would like to use it in production, do some extensive testing first.

Upvotes: 1

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