[5.x] Allow for customizing the attribute used to relate attributes

[Jade-GG]

This is needed for rapidez/statamic where we want to use sku as a primary key (to make sure products always stay attached even after a product re-import which may affect entity ids)

ref: RAP-1727

[royduin]

• We can't use the getKeyName / setKeyName? See: https://github.com/laravel/framework/blob/12.x/src/Illuminate/Database/Eloquent/Model.php
• No impact on performance?

[Jade-GG]

• We can't use the getKeyName / setKeyName? See: https://github.com/laravel/framework/blob/12.x/src/Illuminate/Database/Eloquent/Model.php

Not really, no. When you use getKeyName() you will (of course) get the primary key as defined by the model which we purposefully set to sku: https://github.com/rapidez/statamic/blob/master/src/Models/Product.php#L21

We need both the SKU to be primary key and entity_id for the attribute relation at the same time, so we need to have both. Only way to do that would be to no longer assume that the primary key is always used for that, and instead use a separate variable for that.

• No impact on performance?

Not any that I could tell, especially given that this will only affect the booting part of the model very slightly.

Obviously, if you're using a key that's not indexed it will be slower. However that's not really our problem, and this PR won't really affect that. In this specific case for rapidez/statamic, the SKU field is actually indexed anyway.

[indykoning]

Wouldn't setting the primary key to sku impact more relationships?
Or is it only these that utilise $this->primaryKey for that?

[Jade-GG]

Wouldn't setting the primary key to sku impact more relationships? Or is it only these that utilise $this->primaryKey for that?

Hm, looks like about half of the relations on the product model right now have the entity_id mentioned explicitly. This means relations like tierPrices and reviews will work correctly, but options and reviewSummary will not.

Now I'm not sure if this is the ideal approach. However, I don't know if there's any other way to make this work properly 😞