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100137RE: [XP] [OT] Delegation and YAGNI!

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  • Steven Gordon
    Dec 1, 2004
      Why was this considered OT??

      One way YAGNI applies in this kind of situation is that the stories
      asking for visible business functionality should be separate from
      the stories asking for persistance functionality. Given the
      dependencies between those stories, the business functionality
      stories almost always have greater business value to the customer
      than the persistance stories.

      Persistance is totally YAGNI when implementing the business
      functionality stories, so you first end up with a Customer class
      that provides the visible functionality your customer needs (via
      iterative feedback) with tests that verify its behavior.

      Then, when the persistance stories are the highest priority
      stories not yet implemented, persistance is no longer YAGNI.
      DoSimpleThings, ExpressiveCode, SingleResponsibilityPrinciple,
      etc. will then lead to building a data access layer (or
      leveraging an existing framework). Refactoring (i.e.,
      continuously applying OnceAndOnlyOnce) will keep it as simple
      as possible.

      If the original question was whether having virtually identical
      field names in the Customer object, the database, and the data
      access layer mediating them constitutes duplication, that appears
      to me to be a form of duplication whose elimination would likely
      lead to code that is far more difficult to understand and maintain
      than the code with the duplicative field names.

      Consider CMP in J2EE which is essentially driven by meta-data
      expressed in XML files. I have found CMP frustrating because I
      cannot refactor the code (or the database) without carefully
      editing that XML file. It does not feel like OnceAndOnlyOnce when
      I have to keep the database, code, and XML descriptors in synch.
      Of course, an Eclipse Plugin with XDOCLET-like functionality
      could automate a lot of the synchronization issues away.

      Steven A. Gordon, Ph.D.
      Manager, Software Factory
      Arizona State University
      PO Box 875506
      Tempe, AZ 85287-9509
      http://sf.asu.edu
      (480)-727-6271



      -----Original Message-----
      From: Ramon Leon [mailto:rleon@...]
      Sent: Wednesday, December 01, 2004 11:29 AM
      To: extremeprogramming@yahoogroups.com
      Subject: RE: [XP] [OT] Delegation and YAGNI!



      YouArentGonnaNeedIt is only one of many principles, you have to balance
      it with the others. OnceAndOnlyOnce and DoSimpleThings will lead you to
      making sure each class only has one responsibility, and you are gonna
      need that. YouArentGonnaNeedIt is not a justification to violate basic
      good OO principles like SingleResponsibilityPrinciple. In the java
      community, I'm pretty sure most people just use existing open source
      object mapping layers, in the .NET world, most are still hacking up
      their own private implementation because there isn't any really
      outstanding open source implementations yet.

      > -----Original Message-----
      > From: Stede Troisi [mailto:stedetro@...]
      > Sent: Wednesday, December 01, 2004 9:53 AM
      > To: extremeprogramming@yahoogroups.com
      > Subject: [XP] [OT] Delegation and YAGNI!
      >
      >
      > I was thinking about YAGNI yesterday. Normally, I see most
      > people create a customer class that holds domain information
      > and another class, say CustomerDb that persists the
      > information from customer to a database.
      > This makes sense, becuase if I want to persist to something
      > different (like a flat file) I can create a new class to
      > handle it while leaving the domain class intact.
      >
      > But two objects that share the same basic fields
      > (customer) seems to go against YAGNI. Is this how most people
      > solve the problem or is there a better solution?
      >
      > Thanks,
      > Stede
      >
      >
      >
      >
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