C＃-流利的NHibernate映射问题

Question

Is there a way to avoid the explicit Id mapping in Fluent NHibernate ?

I want it to somehow generate the entry id automatically so that I wouldn't have to introduce it as a part of the class.

public class HeyMapping
{
    public String Name { get; set; }
    public DateTime Timestamp { get; set; }
}

public class HeyMapping : ClassMap<HeyMapping>
{
    public HeyMapping()
    {
        Not.LazyLoad();

        // I'm not particularly sure how this line works, but
        // it fails the mapping unit test.
        CompositeId().KeyProperty(x => x.Name);

        Map(x => x.Name).Not.Nullable().Length(64);
        Map(x => x.Timestamp).Not.Nullable();
    }
}

Answer 1

If you want to have no id in your entity, you still have to map an Id so NHibernate knows the database column to use.

You can call

Id<TColumnDataType>("column_name");

Please note that you will give up some NHibernate functionality (specifically cascading updates and the ability to call SaveOrUpdate() ) and incur a performance penalty on the database side for having database-only identity (I believe NHibernate will have to make extra queries for comparison).

I usually concede this point and allow the Id as the one persistence concern in my domain classes, so I would do this:

public class HeyMapping
{
    protected internal int Id { get; set; } // persistence concern

    public virtual String Name { get; set; }
    public virtual DateTime Timestamp { get; set; }
}

I realize you might not want to do this; I'm just letting you know that there is a tradeoff.

Answer 2

创建一个基类，所有映射的实体都将从该基类继承，然后将Id属性添加到基类。