Associating multiple single instances of the same model in Laravel - php

Question

I am working on a project in which there are events, which each relate to two single forms on two separate relations – booking and survey. These forms are identically constructed, making it seem unnecessary to use two entirely distinct form models – I instead wanted to use a polymorphic relation, but it appears that isn't possible.
What is the appropriate way to structure this relationship?
Events have one or no booking form
Events have one or no survey form
Forms are a separate, single table
What I have tried:
Polymorphic relationship: Not compatible with two relations to the same model.
Has one relationship: This used a booking_id and survey_id but refused to set either of these fields.
Has many relationship with a type field: Made it difficult to easily save the forms, as it wasn't possible to save to the single relationship. There was also no restriction on the number of forms.
class Event extends Model
{
public function booking()
{
return $this->hasOne(Form::class, 'id', 'booking_form_id');
}
public function survey()
{
return $this->hasOne(Form::class, 'id', 'survey_form_id');
}
}
...
class Form extends Model
{
public function event()
{
return $this->belongsTo(Event::class);
}
}
...
$event = new Event;
$event->name = 'Event';
$event->save();
$booking = new Form;
$booking->name = 'booking';
$event->booking()->save($booking);
$survey = new Form;
$survey->name = 'survey';
$event->survey()->save($survey);
...
Schema::create('events', function (Blueprint $table) {
$table->bigIncrements('id');
$table->string('name');
$table->unsignedInteger('booking_form_id')->nullable()->index();
$table->unsignedInteger('survey_form_id')->nullable()->index();
$table->timestamps();
});
Schema::create('forms', function (Blueprint $table) {
$table->increments('id');
$table->string('name');
$table->timestamps();
});
What would be preferable:
Using a polymorphic relationship which would allow forms to be used in other parts of the application.
Using multiple hasOne relationships to limit the number of forms to one for each type.

Answer 1

I think you got your param order wrong. It's hasOne($related, $foreignKey, $localKey)
class Event extends Model
{
/* if you haven't changed the default primary keys, $localKey should be equal to 'id' */
public function booking()
{
return $this->belongsTo(Form::class, 'booking_form_id');
}
public function survey()
{
return $this->belongsTo(Form::class, 'survey_form_id');
}
}
class Form extends Model
{
public function booking_event()
{
return $this->hasOne(Event::class, 'booking_form_id');
}
public function survey_event()
{
return $this->hasOne(Event::class, 'survey_form_id');
}
}
Now there's 2 ways you can go about this.
If a Form can belong to both kind of events, you need to return a collection when accessing $form->event.
If a Form can belong to only one kind of event, you need to guess which kind and return the model when accessing $form->event.
# Form model
# 1. can be achieved using an accessor. Cannot be eager loaded but can be appended with the $appends Model property
public function getEventsAttribute()
{
return collect([$this->booking_event, $this->survey_event]);
}
# Form model
# 2. can be achieved using a relationship that guesses which relation it should return. Since it returns a relationship, it can be eager loaded.
public function event()
{
return ($this->booking_event()->count() != 0) ? $this->booking_event() : $this->survey_event();
}