How can I implement eager load in a many-to-many relationship that exists in a pivot table? I've succeed in retrieving it by lazy loading, but I'm trying to find the eager load way (I'm using L8).

I have 5 tables which related to one another as shown below (simplified):

From the 5 tables above, I've created 4 models:

• Class
• Period
• ClassPeriod, as a pivot model
• Teacher

Class has belongsToMany() relationship to Period, which using() the ClassPeriod pivot model. Common stuff. Eager loads related to these 3 models have been easily done. However, I'm confused on how can I eager load Teacher from Class.

To retrieve Teacher from Class by lazy loading as I mentioned, I've created the following:

• Create teachers method with belongsToMany() relationship in ClassPeriod
• Create getTeachersAttribute method which calls the teachers method above

Then the retrievement can be performed in 2 ways:

• Way number 1 is using the pivot attribute, something like:

  $classes = Class::with(['periods'])->get();
  foreach($classes as $class) {
      echo $class->pivot->teachers;
  }
  

• Way number 2 is by utilizing the appends property in the model. So inside ClassPeriod, I added:

  protected $appends = [ 'teachers' ];
  

  thus Class::with(['periods']) will have teachers appended to the pivot automatically

So, back to the question, how can I achieve the above in eager loads? Is it possible? Your input is much appriciated.

CodePudding user response：

You can call nested relationships with dot . in your with() method.

So your query will be:

Class::with('periods')->with('class_period.teachers');

And create the relationship in Class :

public function class_period(){return $this->hasMany(ClassPeriod::class,'class_id');}

And in your ClassPeriod class the relationship:

public function teachers(){return $this->belongsToMany(Teachers::class)->using(ClassPeriodTeacher::class);}

You can add wheres and whereRelation to add more logic to your query.