getting parent info from child

czuroski · **Joined:** Thu Dec 03, 2009 2:10 pm **Posts:** 13

Hello,
I have 2 mappings defined - parent and child. I am using the following code to retrieve the child info, and this is working fine -

Code:

IList<child> c = myProvider.getChildren();

foreach(var item in c)
{
Console.Writeline(item.myItem);
}

What I need to do, is to get at the parent information for that child. I thought I would be able to do this -

Code:

IList<child> c = myProvider.getChildren();

foreach(var item in c)
{
Console.Writeline(item.parent.myParentItem);
}

but that is coming back as null. How can I access the parent data through a child?

Thanks for any thoughts.

Gorbusch · **Joined:** Tue Jan 05, 2010 12:15 pm **Posts:** 9

Can you post your classes as well as table an mapping

czuroski · **Joined:** Thu Dec 03, 2009 2:10 pm **Posts:** 13

Here is my parent class -

Code:

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="Data" namespace="Data">
  <class name="Data.Parent, Datatable="parent">
    <id name="field1_key">
      <generator class="identity"/>
    </id>
    <property name="field2"/>
    <property name="field3"/>    

    <set name="child" table="child" generic="true" inverse="true">
      <key column="ch_field1_key" />
      <one-to-many class="Data.child, Data"/>
    </set>
    
  </class>  
</hibernate-mapping>

Here is my parent class -

Code:

public class parent
    {
        virtual public int field1_key { get; set; }
        virtual public int field2 { get; set; }
        virtual public int field3 { get; set; }
     }

Here is my child mapping -

Code:

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="Data" namespace="Data">
  <class name="Data.child, Data" table="child">
    <id name="ch_field1_key">
      <generator class="native"/>
    </id>
    <property name="field2"/>    
  </class>
</hibernate-mapping>

and here is my child class -

Code:

public class child
    {
        public virtual int ch_field1_key { get; set; }
        public virtual int field2 { get; set; }

        public virtual parent myParent { get; set; }
     } 

Thanks

wolli · **Posted:** Tue Jan 26, 2010 9:00 am

The mapping for the parent is missing in your child mapping:

<many-to-one name="myParent" ...../>

czuroski · **Joined:** Thu Dec 03, 2009 2:10 pm **Posts:** 13

I have tried adding that in, but then I get an error saying could not execute query - column is not found in any table in the query and it is referencing the key for the parent table.

wolli · **Posted:** Tue Jan 26, 2010 9:58 am

You need a column for the parent id in your child table. It doesn't make sense to have a one-to many association from parent to child, when only one child can exist (you currently use the primary key of the child table).

Have a look at this for mapping parent/child relationships:

http://nhforge.org/doc/nh/en/index.html#example-parentchild

czuroski · **Joined:** Thu Dec 03, 2009 2:10 pm **Posts:** 13

I was able to get it to work. in my child mapping, I was putting the parent key for the column value of the mapping -

Code:

<many-to-one name="Parent" column="parent-key" />

when it should have been set as -

Code:

<many-to-one name="Parent" column="child-key" />

Thanks for all the help.