Component, Dependent or Composition Mapping - Help

kowusu · **Posted:** Tue Feb 06, 2007 4:49 pm

I have class PersonClass that embeds other classes Name and Address (composition). I save the name and address in separate tables from the parent, I am able to save the parent class and it saves the name and address (if any) but when I try to retrieve the parent, the name and address are null.

I believe I am totally misusing the Component and the One-to-One elements. I will appreciate any help or pointers to examples/documentation to read.

My schema looks like below:

table contact
(
[id] int not null identity,
[name_id] int,
[address_id] int
)

table name
(
[id] int not null identity,
[fname] varchar(25),
[lname] varchar(25)
)
table address
(
[id] int not null identity,
[street] varchar(25),
[zip] varchar(25)
)

<class name="Tests.PersonClass" table="contact">
<id name="id" type="Int32" >
<generator class="identity" />
</id>
<component name="person_name" class="Tests.NameClass ">
<property name="id" column="name_id" not-null="false" />
</component>
<component name="person_address" class="Tests.AddressClass ">
<property name="id" column="address_id" not-null="false"/>
</component>

<one-to-one name="person_name" class="Tests.NameClass" cascade="all" constrained="false" lazy="false"/>
<one-to-one name="person_address" class="Tests.Address" cascade="all" constrained="false" lazy="false"/>

</class>

<class name="Tests.NameClass" table="name">
<id name="id" column="name_id" type="Int32" >
<generator class="identity" />
</id>
<property name="fname" column="first_name"/>
<property name="lname" column="last_name"/>
</class>

Code:

public class PersonClass
    {
        private Nullable<int> _id;
        private NameClass _myName;
        private AddressClass _myAddress;

        public PersonClass() { }

        public virtual Nullable<int> id
        {
            get { return this._id; }
            set { this._id = value; }
        }
        public virtual NameClass person_name 
        {
            get { return this._myName; }
            set { this._myName = value; }
        }
        public virtual AddressClass person_address
        {
            get { return this._myAddress; }
            set { this._myAddress = value; }
        }
       
        public virtual Nullable<int> name_id
        {
            get { return this._myName == null ? null : this._myName.id; }
            set { if (this._myName != null)this._myName.id = value; }
        }

        public virtual Nullable<int> address_id
        {
            get { return this._myAddress == null ? null : this._myAddress.id ; }
            set { if (this._myAddress!=null)this._myAddress.id = value; }
        }

    }
    public class NameClass
    {   
        private Nullable<int> _id;
        private string _fname;
        private string _lname;

       public NameClass(){}
        public virtual Nullable<int> id
        {
            get { return this._id; }
            set { this._id = value; }
        }
        public virtual string fname
        {
            get { return this._fname; }
            set { this._fname = value; }
        }
        public virtual string lname
        {
            get { return this._lname; }
            set { this._lname = value; }
        }

    }

mnichols · **Joined:** Mon Aug 21, 2006 9:18 am **Posts:** 179

Do you really need to have the Name class in its own table? I ask because this seems to be overcomplicated. Think of a component as mapping data from within the same table as the parent class, but to different object representations. Personally I'd map your Name class this way in your parent mapping:

Code:

    <component name="person_name" class="Tests.NameClass">
      <property name="fname"/>
      <property name="lname"/>      
    </component>   

If you insist on maintaining the Name in a separate table and must have a one-to-one association, it might look like this:

Code:

<one-to-one name="person_name" class="Tests.NameClass" constrained="true" foreign-key="person_personname" />

It's either a component OR a one-to-one association.

Hope this helps
MIKE

kowusu · **Posted:** Fri Feb 16, 2007 11:18 am

mike,
thanks a lot for your response. I still could not get it to work the way I wanted it though. Part of my problem is that the model is given to me and I can't change it.
But I worked around it by calling SaveOrUpdate() for the Name and Address objects in the Person before I call SaveOrUpdate on the Person object. Somehow I thought I could get NHibernate to do all that for me when I call SaveOrUpdate(personObj).

wolli · **Posted:** Sun Feb 18, 2007 12:30 pm

What does your "new" mapping looks like ? As Mike said, you need either a component or a one-to-one mapping, but not both. If you want Hibernate to save the objects in your collection automatically, you have to add a parent mapping to Name and Adress (Have a look at the reference documentation, chapter 17.1 and 17.2. There is a good example about parent/child relationships).

Regards,
Wolfgang