Question

I haven’t found a clear explanation for what the association method does and how to use it properly — I see several examples where model Alpha has_many Beta and then when creating a new Beta using a Factory we say beta.association :alpha or something along those lines. But isn’t Alpha also associated with Beta (Beta belongs_to Alpha)… so I’m just pretty confused. I thought an association (at least in normal English) is usually mutual, so I am not understanding what this method is supposed to do. Can someone please clarify this?

In addition to understanding it on a broad conceptual level, I would also like to know exactly what it does on a syntactical level (ie. is it adding methods like attr_accessor does? like what is this actually doing??)

Sorry I just have not found a clear explanation for this — if anyone can explain this to me that would be great!!

Answer 1

From my experience you define “association” in FactoryGirl when you need to instantiate associated object while creating other object by factory, and without this association your new object would be invalid.

Let’s say you have Company and Worker models, and in your application you have validations which prevent creating Worker with invalid company_id attribute. You can have Company without workers (that’s why you shouldn’t define association for workers in factory), but you can’t have Worker without Company. You then add association in factory to lazy-instantiate Company for every Worker created.

So to summarize – you define association when you have belongs_to in model, and when your association in model also have presence validation.