Re: mapping 1 to 0 or 1 relationships to null objects

[Ka-Wai Chan]

Thanks Peter
 
We are doing something similar now, was just wondering if this could be
avoided by handling it in IBatis.
 
Thanks
Ka-Wai

>>> Peter Mills <[EMAIL PROTECTED]> 01/22/07 4:24 PM >>>

Hi Ka-Wai,

I find the easiest way to do that kind of mapping is in the domain 
object, itself.

public class Customer {
    SubObject _subObject = SubObject.Empty;

    public SubObject MySubObject {
       get { return _subObject; }
       set {
          if (null == value)
             _subObject = SubObject.Empty;
          else
             _subObject = value;
       }
    }
}

It also protects you from accidentally setting the property null, 
somewhere else in your code.

Cheers,

Peter

Ka-Wai Chan wrote:
> Hello
>  
> I have a 1 to 0 or 1 relationship mapped as follow
>  
>       <result property="SubObject" column="sub_object_id" 
> select="SelectBySubtObjectId"/>
>  
> This works fine, but what we are trying to implement is the
NullObject 
> pattern in which a null value is mapped to a specific null object 
> instead of null.
>  
> ie.  In Parent object, I have a reference called SubObject.  Ibatis 
> right now will set that reference to null when a database value of 
> null is encountered, what I want is for Ibatis to set that value to 
> SubObject.NULL instead.
>  
> Is this possible? What is the proper way of doing this? 
>  
> I have tried implementing ITypeHandlerCallback by doing the following

> but doesn't work.  When is the NullValue getter called?
>  
>         public void SetParameter(IParameterSetter setter, object 
> parameter)
>         {
>         }
>  
>         public object GetResult(IResultGetter getter)
>         {
>             return getter.Value;
>         }
>  
>         public object ValueOf(string s)
>         {
>             return s;
>         }
>  
>         public object NullValue
>         {
>             get { return SubObject.NULL; }
>         }
>  
> Thanks,
> Ka-Wai