[Study Note] Patterns and Practices in NHibernate

在 NHibernate Forge 上，Patterns&Practices 栏目里面只有两篇文章，我感兴趣的是其中一篇：NHibernate and the Unit of Work Pattern。

[Identity Field, Equality and Hash Code]

“The identity field saves a database ID field in an object to maintain identity between an in-memory object and a database row.” – Martin Fowler, PoEAA

The surrogate key is not derived from application data.

GUID, global unique identifier

A Set is a collection that contains no duplicate elements.

a object should never ever change it’s hash code during its life, that is from the moment the object is instantiated until it is disposed.

[NHibernate and the Unit of Work Pattern]

Part 1

Unit of Work Maintains a list of objects affected by a business transaction and coordinates the writing out of changes and the resolution of concurrency problems. – Martin Fowler, PEAA

When you’re pulling data in and out of a database, it’s important to keep track of what you’ve changed; otherwise, that data won’t be written back into the database. Similarly you have to insert new objects you create and remove any objects you delete.

A Unit of Work keeps track of everything you do during a business transaction that can affect the database. When you’re done, if figures out everything that needs to be done to alter the database as a result of your work.

In NHibernate, the Session object is a Unit of Work (UoW) container…Only when flushing the session will the database be alered.

看完之后才发现这个 Unit of Work 的实现过于的复杂，至少现在我还不能完全的理解其中的奥妙。最近几天看到了大概一共三个 Unit of Work 的实现，繁简不一，有时间的话可以比较一下。