Delete / cascade / many to many

santon · **Joined:** Fri May 05, 2006 4:54 am **Posts:** 14

Hello!

I use NHibernate 1.02
I´ve been struggling with this in a couple of days now. But it´s surely a simple question to answer..) I got two tables contact and group, a many to many connection. And a table between named groupcontact.
When I add contacts to a group everything works fine, but how can i delete a contact from the contact table and get the groupcontact table updated with this deletion? I´ve tried with cascade = "delete" but this results in deletion of all contacts and all groups that that contact was tied to. I got inverse = "true" on the group side.

Thanks!

tenwit · **Joined:** Thu Dec 23, 2004 9:08 pm **Posts:** 2008

If you have inverse="true" on the group side, that implies that inverse="false" is on the contact side. So cascade="delete" from contact will delete groups. If you don't want this behvaiour, your options are

to change the direction of the association, and put the inverse="true" on the contact side,
or to turn off cascade="delete".

Rows in the join table are always deleted when you delete corresponding rows from either "main" table. You don't need any special settings for inverse or cascade for this. The inverse and cascade settings affect the "main" tables on the far side of the join table.

santon · **Joined:** Fri May 05, 2006 4:54 am **Posts:** 14

Thanks for the answer! But still I cant´t get it to work..
With the code below, only the contact is deleted from the main table.

Code:

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.0" namespace="Business" assembly="Business">
  <class name="Business.Contact, Business" table="Contact" >
    <id name="Id" column ="id" type="System.Int32" >
      <generator class="native" />
    </id>
    <property name="FirstName" />
    <property name="LastName"/>
    <property name="EMail"/>
    <property name="TelePhone"/>
    <property name="UserName"/>
    <property name="Picture" type="BinaryBlob"/>
    <bag name="Groups" table="GroupContact" inverse="true" lazy="true">
      <key column="contactid" />
      <many-to-many class="Business.Groups, Business" column="groupid" />
    </bag>
  </class>
</hibernate-mapping>

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.0" namespace="Business" assembly="Business">
  <class name="Business.Groups" table="Groups">
    <id name="GroupId" column="groupId" type="System.Int32">
      <generator class="native" />
    </id>
    <property name="GroupName" type="String" />
    <property name="UserName" type="String" />
    <bag name="Contacts" table="GroupContact" cascade="delete" lazy="true">
      <key column="groupid" />
      <many-to-many class="Business.Contact, Business" column="contactid" />
    </bag>
  </class>
</hibernate-mapping>

In code I do this:

Contact p = (Contact)session.Load(typeof(Contact), Convert.ToInt32(contacts[i].ToString()));
                    session.Delete(p);
                    session.Flush();

tenwit · **Joined:** Thu Dec 23, 2004 9:08 pm **Posts:** 2008

That code is deleting contact p but leaving references to it in the GroupContact table? That doesn't happen in my code, which admittedly is hibernate3.

I would expect your current mapping to delete any GroupContact rows when the relevant Contact is deleted, and to delete any Contacts and GroupContact rows when a Group is deleted.

Try changing the bags to sets. I've never used bags in production code because of their inefficiencies (inserting or deleting items is very expensive for bags), so it's possible that what you're seeing is correct behaviour for bags. Unlikely, though...

scarface · **Joined:** Sun Jun 04, 2006 1:58 am **Posts:** 136

I think tenwit got it backwards ,
make
inverse="true" and cascade="none"
and
inverse ="false"

on groups. That should get it to work

santon · **Joined:** Fri May 05, 2006 4:54 am **Posts:** 14

Yes! It worked the way scareface said. Thank you both!

tenwit · **Joined:** Thu Dec 23, 2004 9:08 pm **Posts:** 2008

Not backwards, upside down! It's what we do, here on the underside of the world.

That's my excuse and I'm sticking to it ;)

sriguru · **Joined:** Fri May 11, 2007 11:03 am **Posts:** 32

I was trying the same thing.But deleting the relationship works fine if have cascade =none and inverse=true on one side but the addition of one object to the other stops working . For addition I have to set it to "all-delete-orphan"
I am doing something wrong?