When working with objects that are saved to a database that have a relationship, do you load the whole objects or just the id?

Suppose I have a CatHerder and he has Cats, when I getCatHerderByID(String id) should I load in the CatHerder and set an arrayList of cats or an arrayList of cat开发者_JS百科IDs?

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getCatHerderByID() should be a method which returns an object of type CatHerder, which can have a property catsOwned which will contain a list of IDs, populated by the constructor. In addition, you can have a method on the CatHerder object called getCats() which returns an array of Cat consisting of the IDs in the CatHerder object. You shouldn't load unnecessary information just because it has a relationship with the information you actually want -- in many cases, everything will have a relationship with the data you actually want.

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When you don't have much data or many concurrent users, you can go with either way.

One easy options would be to add an additional parameter specifying whether to return a "deep copy" including the relations, or just the attributes of the object itself.

Stay away from the urge to add more parameters, or you will end up re-implementing SQL :)