Laravel – Eager Loading Polymorphic Relation’s Related Models

Solution:

It is possible, if you add:

protected $with = ['company']; 

to both the Service and Product models. That way, the company relation is eager-loaded every time a Service or a Product is loaded, including when loaded via the polymorphic relation with History.

Explanation:

This will result in an additional 2 queries, one for Service and one for Product, i.e. one query for each historable_type. So your total number of queries—regardless of the number of results n—goes from m+1 (without eager-loading the distant company relation) to (m*2)+1, where m is the number of models linked by your polymorphic relation.

Optional:

The downside of this approach is that you will always eager-load the company relation on the Service and Product models. This may or may not be an issue, depending on the nature of your data. If this is a problem, you could use this trick to automatically eager-load company only when calling the polymorphic relation.

Add this to your History model:

public function getHistorableTypeAttribute($value)
{
    if (is_null($value)) return ($value); 
    return ($value.'WithCompany');
}

Now, when you load the historable polymorphic relation, Eloquent will look for the classes ServiceWithCompany and ProductWithCompany, rather than Service or Product. Then, create those classes, and set with inside them:

ProductWithCompany.php

class ProductWithCompany extends Product {
    protected $table="products";
    protected $with = ['company'];
}

ServiceWithCompany.php

class ServiceWithCompany extends Service {
    protected $table="services";
    protected $with = ['company'];
}

…and finally, you can remove protected $with = ['company']; from the base Service and Product classes.

A bit hacky, but it should work.