Laravel Eloquent: Eager Load Pivot Relations

Eager load pivot relations for Laravel Eloquent's BelongsToMany relation.
Medium Story: https://medium.com/@ajcastro29/laravel-eloquent-eager-load-pivot-relations-dba579f3fd3a

Installation

composer require ajcastro/eager-load-pivot-relations

Usage and Example

There are use-cases where in a pivot model has relations to be eager loaded. Example, in a procurement system, we have the following:

Tables

items
 - id
 - name

units
 - id
 - name (pc, box, etc...)

plans (annual procurement plan)
 - id

plan_item (pivot for plans and items)
 - id
 - plan_id
 - item_id
 - unit_id

Models

class Unit extends \Eloquent {
}

use AjCastro\EagerLoadPivotRelations\EagerLoadPivotTrait;
class Item extends \Eloquent
{
    // Use the trait here to override eloquent builder.
    // It is used in this model because it is the relation model defined in
    // Plan::items() relation.
    use EagerLoadPivotTrait;

    public function plans()
    {
        return $this->belongsToMany('Plan', 'plan_item');
    }
}

class Plan extends \Eloquent
{
    public function items()
    {
        return $this->belongsToMany('Item', 'plan_item')
            ->using('PlanItem')
            // make sure to include the necessary foreign key in this case the `unit_id`
            ->withPivot('unit_id', 'qty', 'price');
    }
}


// Pivot model
class PlanItem extends \Illuminate\Database\Eloquent\Relations\Pivot
{
    protected $table = 'plan_item';

    public function unit()
    {
        return $this->belongsTo('Unit');
    }
}

From the code above, plans and items has Many-to-Many relationship. Each item in a plan has a selected unit, unit of measurement. It also possible for other scenario that the pivot model will have other many relations.

Eager Loading Pivot Relations

Use keyword pivot in eager loading pivot models. So from the example above, the pivot model PlanItem can eager load the unit relation by doing this:

return Plan::with('items.pivot.unit')->get();

The resulting data structure will be:

You may also access other relations for example:

return Plan::with([
  'items.pivot.unit',
  'items.pivot.unit.someRelation',
  'items.pivot.anotherRelation',
  // It is also possible to eager load nested pivot models
  'items.pivot.unit.someBelongsToManyRelation.pivot.anotherRelationFromAnotherPivot',
])->get();

Custom Pivot Accessor

You can customize the "pivot accessor", so instead of using the keyword pivot, we can declare it as planItem. Just chain the as() method in the definition of the BelongsToMany relation.

class Plan extends \Eloquent
{
    public function items()
    {
        return $this->belongsToMany('Item', 'plan_item')
            ->withPivot('unit_id', 'qty', 'price')
            ->using('PlanItem')
            ->as('planItem');
    }
}

Make sure we also use the trait to our main model which is the Plan model, because the package needs to acess the belongsToMany relation (items relation) to recognize the used pivot acessor.

use AjCastro\EagerLoadPivotRelations\EagerLoadPivotTrait;

class Plan extends \Eloquent
{
    use EagerLoadPivotTrait;
}

So instead of using pivot, we can eager load it by defined pivot accessor planItem.

return Plan::with('items.planItem.unit')->get();

$plan = Plan::with('items.planItem.unit');

foreach ($plan->items as $item) {
    $unit = $item->planItem->unit;
    echo $unit->name;
}

Other Examples and Use-cases

https://github.com/ajcastro/eager-load-pivot-relations-examples