In laravel, what happen if we define hasMany() relationship but didn't define belongsTo() relationship?

Question

I think (I don't really know, if I'm wrong please correct me), this is actually Many To Many relationship between Medias table and other tables (Users, Messages, Posts).

So, I am creating the middle table named Media_links to connect the Many To Many relation between these tables.

I am thinking to define the hasMany() relation for the Medias tables, but didn't want to define its belongsTo() relationship.

I didn't try anything yet. Posting this thread just to get insights first.

Answer 1

hasMany and belongsTo is a one-to-many, NOT many-to-many.

about your question, you can access the relation whereever you define it, but not the inverse unless you define it!

i.e. if you have a Teacher and Student model

Teacher Model

use Illuminate\Database\Eloquent\Relations\HasMany;

class Teacher extends Model {

    public function students(): HasMany {
        return $this->hasMany(Student::class);
    }
}

Student Model

use Illuminate\Database\Eloquent\Relations\BelongsTo;

class Student extends Model {

    //Relation below not define.
    /* public function teacher(): BelongsTo {
        return $this->belongsTo(Teacher::class);
    } */
}


//each line below works fine, you can perform relationship related query 
$teacher->students()->create([...]); // create students relation
$teacher->students; //lazy load students relation
Teacher::with('students')->paginate(); //eager load students relation


//each line below will throw 500 error as Inverse relation is not define 
$student->teacher()->create([...]); // create teacher relation
$student->teacher; //lazy load teacher relation
Student::with('teacher')->paginate(); //eager load teacher relation