Confused about mapping

vishyanand · **Joined:** Fri Jul 07, 2006 12:08 pm **Posts:** 37

I have this scenario-A TransportPackage can have many vehicle hire rates.So,my mapping looks like

Code:

  <class name="TransportPackage" table="TransportPackages" lazy ="false" >
    <id name="m_TransportPackageID" column ="TransportPackageID" access ="field">
      <generator class ="identity"></generator>
    </id>

    <property name="TransportPackageName" />
    <many-to-one name="m_Destination" access ="field" class="Destination"  column ="TransportPackageLocationID"/>
    
    <property name="TransportPackageNoOfDays"/>
   
 
    </bag>
    <bag name ="m_VehicleHireRateCollection" access ="field"  table="TransportPackageVehicleRates" cascade ="all-delete-orphan">
      <key column ="TransportPackageID"></key>
      <one-to-many class ="VehicleHireRate" />
    </bag>

  </class>

and in another hbm..VehicleHireRate

Code:

<class name="VehicleHireRate" table="TransportPackageVehicleRates" lazy ="false">
    <id column ="TransportPackageVehicleRateID" name ="m_VehicleHireRate" access ="field">
      <generator class ="identity"/>
    </id>

    <property column ="TransportPackageVehicleRateBaseCost" name ="m_BaseCost" access ="field"/>
 
    <many-to-one class ="TransportPackage" column ="TransportPackageID" name ="m_TransportPackage" access ="field"></many-to-one>
  </class>
 

Now,if I remove many-to-one mapping from vehicleHireRate,I get an error while inserting into VehicleHireRate table,cannot insert null for TransportPackageID.Does it mean,that both sides of relationship must hav references to each other
thks

GeAr · **Posted:** Thu Sep 07, 2006 5:01 am

How do you ‘insert’ into VehicleHireRate? When you create a VehicleHireRate object, set its properties (among which the TransportPackage property) and flush the session, then you will need the bi-directional relationship. If you add a VehicleHireRate object to the VehicleHireRateCollection of the TransportPackage, either explicitly or by some AddVehicleHireRate method, you can do without the bi-directional relationship (which I usually prefer), but then you must allow the database column TransportPackageVehicleRates.TransportPackageID to be null. See NHibernate doc on One-To-Many Associations.

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

Have you tried putting inverse='true' in your collection declaration?
Like so:

<bag name ="m_VehicleHireRateCollection" access ="field" table="TransportPackageVehicleRates" cascade ="all-delete-orphan" inverse="true">
<key column ="TransportPackageID"></key>
<one-to-many class ="VehicleHireRate" />
</bag>

Then you can drop the many-to-one association but the key from TransportPackage should be in the TransportPackageVehicleRates table.

MIKE

vishyanand · **Joined:** Fri Jul 07, 2006 12:08 pm **Posts:** 37

Hi Mike,
I did what you said,I get error cannot insert null..when I add VehicleHireRate and save it..

mnichols wrote:

Have you tried putting inverse='true' in your collection declaration?
Like so:

<bag name ="m_VehicleHireRateCollection" access ="field" table="TransportPackageVehicleRates" cascade ="all-delete-orphan" inverse="true">
<key column ="TransportPackageID"></key>
<one-to-many class ="VehicleHireRate" />
</bag>

Then you can drop the many-to-one association but the key from TransportPackage should be in the TransportPackageVehicleRates table.

MIKE

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

Sorry - I was wrong...I just had to get this for a mapping myself.
Per the Hibernate In Action book, when you don't have bidirectional association for a one-to-many, then the foreigh keey column (TransportPackageID) must be null. They admit that is confusing from a relational point of view since typically you'd make it non-nullable, but they argue that since you don't have a bidirectional association in the object, then it is conciveable that the VehicleHireRate would exist on it's own as far as NHibernate is concerned.
So you have a choice - either allow nulls in your foreign key column which may not be a big deal (and remove the inverse='true' flag, or set up the bidirectional association.

I applied this to my mappings as well and am deleting, saving, and updating without bidirectional associations.

Hope this helps.

MIKE