laravel one-to-many on pivot table

Question

I have a four table which are institutions, forms, form_institution(pivot table) and form_institution_attributes. Here is migrations :

Institution Table :

public function up() {
     Schema::create('institutions', function (Blueprint $table) {
         $table->increments('id');
         $table->string('name', 255);
         $table->softDeletes();
         $table->timestamps();
     });
 }

Institution model :

public function forms() {
    return $this->belongsToMany(Form::class, 'form_institution');
}

Form Table :

public function up() {
    Schema::create('forms', function (Blueprint $table) {
        $table->increments('id');
        $table->string('name', 255);
        $table->softDeletes();
        $table->timestamps();
    });
}

Form Model :

public function institutions() {
    return $this->belongsToMany(Institution::class, 'form_institution');
}

Form Institution Pivot Table :

Schema::create('form_institution', function (Blueprint $table) {
    $table->increments('id');
    $table->integer('institution_id')->unsigned();
    $table->integer('form_id')->unsigned();

    $table->foreign('institution_id')->references('id')->on('institutions');
    $table->foreign('form_id')->references('id')->on('forms');
});

Everything is ok till here. But i need to add one more table which is attribute table and it's relationship between pivot table (one-to-many)

Here is table :

Schema::create('form_institution_attributes', function (Blueprint $table) {
            $table->increments('id');
            $table->integer('form_institution_id')->unsigned();
            $table->integer('field_name_id')->unsigned();
            $table->integer('input_type_id')->unsigned();
            $table->string('field_caption');
            $table->softDeletes();
            $table->timestamps();

            $table->foreign('form_institution_id')->references('id')->on('form_institution');
        });

Now, when i call the institution table and institution->forms parameter, i want to get form_institution_attribute (sub-table) with pivot table. But i couldn't do this ?

How can i add table under pivot table as a one-to-many relation ?

Answer 1

You should be able to use the HasManyThrough type of relationship.

However, I think the best solution would be to add these attributes to extra columns that you create in your 'form_institution' table and then retrieve them much more easily by adding the withPivot method to your relationship definitions.

So that would look like this:

public function forms() {
    return $this->belongsToMany(Form::class, 'form_institution')
        ->withPivot([
            'field_name_id',
            'field_caption'.
            ...
        ]);
}

public function institutions() {
    return $this->belongsToMany(Institution::class, 'form_institution')
        ->withPivot([
            'field_name_id',
            'field_caption'.
            ...
        ]);
}