C# - Fluent NHibernate mapping question

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();
    }
}

Jay · Accepted Answer · 2010-12-17 17:29:06Z

2

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.

edited Dec 17, 2010 at 17:29

answered Dec 17, 2010 at 17:15

Jay

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ryudice · Accepted Answer · 2010-12-17 16:56:50Z

1

Create a base class from which all of your mapped entities inherit, then add an Id property to your base class.

answered Dec 17, 2010 at 16:56

ryudice

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