Application Generation - ORM

Polymorphic Queries

Mon, 14 Jul 2008 17:14:00 -0400

One thing that is quite nice in Hibernate is the support for polymorphic queries. Let's say that I have a number of companies that I do business with - vendors and customers. They may be in different tables (lets say tbl_Vendor and tbl_Customer) if I implement a "one table per concrete class" inheritance strategy, but I can still query for all of the Companies that I do business with. If I'm using one table per concrete class, Hibernate uses a union of two queries plus the setting of null columns (to give vendors the customer columns and vice versa) to return the results of the query. Obviously if I'm using one table per class hierarchy, Hibernate can just run a simple query against the tbl_Company table to get the results.

Default Values

Mon, 14 Jul 2008 16:36:00 -0400

Continuing on from an earlier posting, I'm looking at the different meaning of "default values" within an application and some ways of distinguishing them . . . [More]

Some More Persistence Patterns

Mon, 14 Jul 2008 14:53:00 -0400

Some other interesting ideas from Hibernate: serializable Value object classes, properties utilizing a SQL formula, generated property types, and default values . . . [More]

Inheritance in Hibernate: Should an Object Ever Have More than one Type?

Mon, 14 Jul 2008 14:36:00 -0400

Let's say you have an inheritance hierarchy where Vendor and Customer are both subclasses of Company. So, you deal with companies that could be Vendors or Customers. The question is, what happens if a given Company is both a Vendor and a Customer? . . . [More]

Object LifeCycles: Value Objects, Composed Objects and Associated Objects

Mon, 14 Jul 2008 12:55:00 -0400

When thinking about persistence, one of the concerns is the lifecycles of the objects you are persisting (necessary to understand how/when to implement cascading deletes) . . . [More]

Entity vs Value Types in Hibernate

Mon, 14 Jul 2008 12:31:00 -0400

Hibernate is really the gold standard for ORM's, and if you have any interest in persisting object models it makes sense to study Hibernate - whether to use it or to learn from the patterns that they use. One interesting pattern in Hibernate is the distinction between Entity and Value object types . . . [More]

How Would You Solve the Order:Address Problem?

Mon, 14 Jul 2008 11:18:00 -0400

Let's say you're building a commerce system. An Order has a BillingAddress. You want to support address book functionality where users can re-use, edit and delete addresses, but once an order has been placed, you want to fix the BillingAddress for that order while still allowing it to be editable within the address book. What's the best way to solve the problem? . . . [More]

What Should a Persistence Framework Do?

Mon, 14 Jul 2008 10:52:00 -0400

At its simplest, the goal of a persistence framework is to simplify and speed up the process of handling persistence of your applications. What a persistence framework needs to do depends heavily on your use cases. Here are the core problems I would personally like a persistence framework to solve . . . [More]

Objects, Tables and ORMs – part deux

Thu, 03 Apr 2008 10:30:00 -0400

The other day I looked at inheritance strategies for ORMs. Today I want to look at some of the other times where there isn't necessarily a 1:1 relationship between objects and database tables . . . [More]

Objects, Tables and ORMs

Wed, 02 Apr 2008 16:01:00 -0400

One of the quickest tests of an ORM is to look at how flexible it is when mapping objects to tables. Here are some of the possible requirements to consider . . . [More]

What I Need From My ORM/Data Access Layer

Fri, 24 Aug 2007 22:55:00 -0400

The ideal ORM is dependent on your exact use case. From Transfer and Reactor to SQL Alchemy and Hibernate, there are many ORM systems available of varying complexity. Here's what I need from my ORM system. I'd appreciate any input on features I haven't mentioned along with a sense of the problem they solve. This spec works for me today, but I'm sure there are plenty of new use cases just lurking out of site that I haven't thought through yet :-> . . . [More]

Approaches to ORM . . .

Mon, 28 May 2007 13:18:00 -0400

Phillip Senn posted a link to Paul Nielsons Nordic ORM for .NET, and I just came across a nice overview of SQL Alchemy - a Python ORM. Always interesting to see different approaches to these common problems . . .

Microsoft Gets Into ORM

Fri, 04 May 2007 12:28:00 -0400

It appears that with Project Jasper, Microsoft is getting into ORM. Right now this will only work with VB9 and IronPython (and possibly Managed Javascript and Iron Ruby) due to the dependence on late binding so it isn't exactly going to take the commercial world by storm just yet, but it'll be interesting to check out their API and to see how this ends up working down the line with the Dynamic Language Runtime. Interesting times!

Rethinking the Data Access Layer

Thu, 22 Mar 2007 11:40:00 -0400

There are a number of approaches to implementing a data access layer. You're got procedural tools like Steve Bryants excellent DataMgr and ORM systems like the extremely popular Transfer from Mark Mandell and Reactor from Doug Hughes. In this short series I want to examine exactly what I need out of a DAL and how I plan to approach solving this problem in a somewhat different way that Steve, Mark or Doug have taken . . . [More]

A DSL for SQL

Tue, 13 Mar 2007 14:56:00 -0400

Written in Ruby, but looks interesting. Will have to compare to Mark Mandells TQL (part of Transfer) and Doug Hughes' query object API and see what I can learn . . .