Call to a member function addEagerConstraints() on string

问题

I want to calculate the average of the column of nested morph relation.

Model Function

public function trader_ratings()
{
    return $this->morphMany(TraderRatings::class, 'rateable')
        ->select('rateable_id', 'rateable_type', 'rating')
        ->avg('rating');
}

Controller with lazy loading

$user = auth('api')->user();
$user_id = $user->id;
$customer_classes = CustomerClassBooking::with([
    'trader_class',
    'trader_class.trader_ratings',
    'vendor',
])
    ->where('customer_id', $user_id)
    ->where('status', 'Accepted-paid')
    ->get();

It is not calculating the avg but giving the error.

回答1:

Because with() need to get the relationship. addEagerConstraints is from source code. When you use eager loading, Your relationship builder will call addEagerConstraints.

However, your relationship method is return the string(the result of avg()) instead of morph relationship. So the error occurs.

You can change your method like:

public function trader_ratings()
{
    return $this->morphMany(TraderRatings::class, 'rateable')->select('*', DB::raw('AVG(rating) AS avg_rating'));
}

回答2:

The error clearly states that trader_ratings have already calculated the avg and is no longer instance of builder that you would need for eager loading. so may be do some thing as below, (not tested the code, just from top of my head)

public function trader_ratings()
{
  return $this->morphMany(TraderRatings::class, 'rateable')->select('rateable_id','rateable_type','rating');
 }


// Then

$customer_classes = CustomerClassBooking::with([
         'trader_class',
         'trader_class.trader_ratings' => function($query`){
            $query->avg('rating)
         },

        ,'vendor'])-> // rest of query

来源：https://stackoverflow.com/questions/59897448/call-to-a-member-function-addeagerconstraints-on-string