Filter through model or dao?

Question

How should I filter a series of domain objects according to user-defined criteria? Should filtering methods be in the model or should be in the DAO?

Answer 1

If you want to use only model objects (mostly) as data containers, you should put a filter in the DAOs that you already use. It’s good practice to make sure that user criteria are independent of the database (so pass your own filter object, not a simple one like Hibernate Criteria. An example query may work fine too).

Then your DAO methods might look like this:

public interface BeanDao
{
    List<Bean> findAllByFilter(BeanFilter filter);
}

Answer 2

The choice of whether to retrieve more objects and then filter or just retrieve the correct objects in the first place depends on the underlying data. Most applications will use a combination of the two.

I would consider the following things:

Network bandwidth and memory requirements

If after filtering there are a small number of results, but a significantly larger number of results before filtering, then this can be a waste of resources and memory resources for filtering in code.

Request speed

Filtering results in a database can be more expensive than executing logic in code — disk and memory. Indexes are needed to make this useful.

maintainability

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