Comments on: What’s persistence got to do with it ?

By: Udi Dahan - The Software Simplist

Udi Dahan - The Software Simplist — Mon, 02 Feb 2004 02:38:07 +0000

Paul,

Let me get this straight – you’re dirtying up the one thing common to the whole system ( and external systems that will work in concert with it ) to ease the implementation of ONE service ?!

That’s like amputating your arm to save yourself from having to cut the fingernails on your hand !

By: paulb

paulb — Sun, 01 Feb 2004 22:33:40 +0000

I built something similar recently, but chose to use attributes on my entity classes to guide the CRUD-methods in my service.

By: Udi Dahan - The Software Simplist

Udi Dahan - The Software Simplist — Thu, 22 Jan 2004 03:14:56 +0000

I have yet to implement something like you describe, however, if the business need is to support dynamic/complex queries, this does point to a QueryService.

The fact that the QueryService uses the database does NOT mean that it must use the PersistenceService. Contrast this with the N-Layer model, where all calls to the database would go through the same DAL.

By: Johnny Hall

Johnny Hall — Wed, 21 Jan 2004 23:06:46 +0000

This is very similar to the architecture that I built (on VB6, XML, COM+). How would you fit this into your SOA Udi? A QueryService?

By: mike lorengo

mike lorengo — Wed, 21 Jan 2004 22:31:42 +0000

Martin Fowler proposes using a Query Object http://www.martinfowler.com/eaaCatalog/queryObject.html for this purpose. A query object being composed of Criteria objects. For a more detailed discussion buy his book, you won’t regret it, or subscribe to safari.informit.com like I do.

By: Johnny Hall

Johnny Hall — Wed, 21 Jan 2004 20:15:47 +0000

I’m working on something similar at the moment, with regards to persistence. I have a question:

When you Read data, how do you deal with more complex queries? Using the entity as the query parameters is fine, as long as you don’t require anything more complex, e.g. different logical operators (how do you specify AND/OR?).

In a previous architecture, I had a query script constructed from XML, which the DAL deconstructed and built the SQL (in a nutshell). A class allowed the developer to specify query parameters, operators, etc.

I’m thinking of creating a generic “search” method which will accomplish something similar to this.

What’s your approach?