Top 10 Must Have Features in O/R Mapping Tools
Feature 2: Use your existing domain objects
As you saw, a popular design pattern separates persistence objects into "domain" and "factory" objects. One important O/R mapping feature is to let you decide whether you want to generate both domain and factory objects or use your existing domain objects and only generate factory objects that know about your domain objects.
Some people do not want to generate "domain" objects and instead develop them by hand and only generate the "factory" objects. The reason behind this is that their domain objects are being used in almost all subsystems of their application and therefore they don't want them changing frequently through subsequent code regenerations. But, they don't mind generating the "factory" objects since their use is localized to a few places (for load and save operations).
Therefore, the O/R mapping tool should let you use your existing domain objects and map and generate only the factory objects. It should use .NET Reflection to read your domain object definition and after you have done the mapping, it should generate the factory objects in such a way that these factory objects use your domain objects to hold all the data.
Feature 3: Transactional operations (CRUD)
A database transaction allows you to group multiple operations as one atomic operation so either all operations succeed or none of them succeed. Transactional operations include create, read, update, and delete (also called insert, update, load, and delete). Each transaction operation is performed only on one row of data in a table.
You'll be working in one of two main transactional environments and your O/R mapping tools needs to know both of them so it can generate code accordingly. They options are:
- COM+/MTS
Microsoft Transaction Server (MTS) manages all transactions of an application. Your objects do not start, commit, or rollback a transaction. They only return success or failure from their methods and MTS figures out when to do "BeginTrans", "Commit", or "Rollback". Additionally, all your factory objects are stateless so MTS can do object pooling on them. This is a specific design pattern that your O/R mapping tool must understand and generate your persistence objects to comply with it. Most common applications for this environment are ASP.NET applications and .NET Web Services. - Stand-alone
This is the environment where your application manages all the transactions itself. It needs to know where to go "BeginTrans", "Commit", and "Rollback". And, your O/R mapping tool needs to be aware of this environment and generate code to comply with it. Most common situations for this are Windows Forms based client/server applications that directly talk to the database server.
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