用NHibernate进行类映射

Question

I have a plain database table (Named DBFoo):

| PropertyA | PropertyB| PropertyC | PropertyD | PropertyE |

PropertyA, PropertyB and PropertyC are part of the key.

And for this in my program I have following class structure:

public class Foo
{
   public virtual SubFoo SubFoo { get; set; }
   public virtual string PropertyC { get; set; }
   public virtual string PropertyD { get; set; }
   public virtual string PropertyE { get; set; }
}

public class SubFoo
{
   public virtual string PropertyA { get; set; }
   public virtual string PropertyB { get; set; }
}

Now I'm trying to create the mapping file:

...
<class name="Foo" table="DBFoo">
   <composite-id>
      // here I Need to define the mapping for the SubFoo properties PropertyA and PropertyB
      <key-property name="PropertyC" column="PropertyC"/>
   </composite-id>
   <property name="PropertyD" column="PropertyD"/>
   <property name="PropertyE" column="PropertyE"/>
</class>
....

Anyone an idea how I can define the key-properties for the PropertyA and PropertyB?

Thanks in advance for helping

Answer 1

Possibly is a bad idea, but you can try to generate a FooIdentifier class that decorates your SubFoo class to provide direct access to PropertyA , PropertyB and PropertyC .

public class FooIdentifier
{
    private SubFoo InnerSubFoo { get; set; }
    public FooIdentifier(SubFoo subFoo, string propertyC)
    {
        this.InnerSubFoo = subFoo
        this.PropertyC = propertyC;
    }   

    public virtual string PropertyA 
    { 
        get 
        { 
            return SubFoo.PropertyA; 
        } 
        set 
        {
            SubFoo.PropertyA = value; 
        }
    }

    public virtual string PropertyB
    {
        get
        {
            return SubFoo.PropertyB; 
        }
        set 
        {
            SubFoo.PropertyB = value;
        }
    }

    public virtual string PropertyC { get; set; }
}

Then, the mapping file could be something like:

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2">
  <class name="Foo" table="Foo" lazy="true" >
    <composite-id name="FooIdentifier" class="FooIdentifier">
      <key-property name="PropertyA" column="PropertyA" />
      <key-property name="PropertyB" column="PropertyB" />
      <key-property name="PropertyC" column="PropertyB" />
    </composite-id>
    <property name="PropertyD" column="PropertyD" type="String" />
    <property name="PropertyE" column="PropertyE" type="String" />
  </class>
</hibernate-mapping>

Answer 2

As HuorSwords mentioned, you can define a composite key for your table, to do this, you have to create a composite key class which contains the properties AND overwrites the hashkey and equals methods...

Read this blog for further details of how exactly this should be implemented.

But I would strongly recommend not to use composite keys because there can be some issues in general. In addition it is recommended to have a surrogate key more or less in each table and have secondary keys/foreign keys where needed.

This makes also the nhibernate mappings a lot easier!