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Best practice for DAO pattern?

Asked 2010-03-18T09:14:16.403
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I've seen a lot of codes use a service-dao pattern , I don't know the origin of this pattern . It force the front layer call service , then delegates some of the service task to dao.

I want to ask :

  1. Does DAO layer do purely data access related task ? What about things like exception encapsulation?
  2. Is there any other pattern can be used to replace this or better than this ?
  3. I think pojo domain models and transaction scripts make even simple problem became complicated , is it possible to completely eliminate dao layer ?
architecture domain-driven-design design-patterns dao
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The main goal of such a layer is to provide abstraction of the persistance back-end. however, most of the times, due to specificities of persistance back-end, total hiding is not possible; A typical example is the query handling. To query a DB using hibernate, you'll write some kind of query code (using HQL, query API, ...) and a totally different paradigm when using JCR, a BigTable, or something else. As a consequence, most of the time, this pattern fails.

Besides there is also the - more annoying - issue of DAO/DTO. You are then pushed forward to write a first class holding your data, then a second copying data from your first one without any added value just for the sake of layer isolation.

There is however some work that has been done in this field. For a micro-framework i've started and implemented for google-app-engine, I've made a little list of so-called dao frameworks easying this rather mundane code.

Notice I plan, in the future, to be able to offer total transparency through gaedo service definition, but it's only a hope ;-) (and is not of immediate interest to you, I guess).

answered 2010-03-18T09:21:38.873

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