Having Problem with Many to Many Mapping

sandipandeb · **Joined:** Mon Oct 17, 2005 1:58 am **Posts:** 27

I am trying to implement a many to many mapping between two table objects by introducing an intermediate link table. When I insert data into the two main tables I want the data to be inserted or updated automatically into the link table.

But data is not automatically inserted into the link table.Ihave to manually insert it.

Can anybody help me in this regard?

Thanks..

michal · **Posted:** Wed Dec 28, 2005 3:52 am

Properly mapped many-to-many collection should maintain "link table" transparently.

Could you post a code sample (your mapping at least)?

sandipandeb · **Joined:** Mon Oct 17, 2005 1:58 am **Posts:** 27

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.0" default-access="nosetter.camelcase">
<class name="QandADomainModel.QandAAuthenticationQuestion, QandADomainModel" table="QA_AUTHENTICATION_QUESTIONS" >
<id name="Id" column="QUESTION_ID" type="Int32" unsaved-value="0">
<generator class="native"/>
</id>
<property name="Text" column="TEXT" type="string" not-null="true" />
<property name="QuesLanguage" column="QUES_LANGUAGE" type="string" not-null="true" />
<property name="CreatedDate" column="CREATION_DATE" type="DateTime" not-null="true" />
<many-to-one name="QAClientApp" column="QA_CLIENT_APP_ID" class="QandADomainModel.QandAClientApplication, QandADomainModel" not-null="true" />
<property name="Status" column="STATUS" type="string" not-null="true" />
<bag name="QAAuthAnswers" lazy="false" inverse="false" cascade="all-delete-orphan" >
<key column="QUESTION_ID"/>
<one-to-many class="QandADomainModel.QandAAuthenticationAnswer, QandADomainModel"/>
</bag>
<bag name="QAUsers" table="QA_QUESTIONS_USERS" inverse="false" >
<key column="QUESTION_ID" />
<many-to-many column="USER_ID" class="QandADomainModel.QandAUser,QandADomainModel" />
</bag>
</class>

<class name="QandADomainModel.QandAUser, QandADomainModel" table="QA_USERS">
<id name="Id" type="Int32" column="USER_ID">
<generator class="native" />
</id>
<bag name="QAAuthenticationQuestions" table="QA_QUESTIONS_USERS" lazy="true" inverse="true" >
<key column="USER_ID" />
<many-to-many column="QUESTION_ID" class="QandADomainModel.QandAAuthenticationQuestion,QandADomainModel" />
</bag>
<property name="UserName" column="USER_NAME" type="String" />
<property name="CreationDate" column="CREATION_DATE" type="DateTime" />
<property name="Status" column="STATUS" type="String" />
<many-to-one name="QAClientApplication" column="CLIENT_APP_ID" class="QandADomainModel.QandAClientApplication, QandADomainModel" />
</class>

<class name="QandADomainModel.QandAClientApplication,QandADomainModel" table="QA_CLIENT_APPLICATIONS" >
<id name="Id" column="QA_CLIENT_APP_ID" type="Int32" unsaved-value="0" >
<generator class="native"/>
</id>

<property name="QAClientApplication" column="QA_CLIENT_APPLICATION_NAME" type="string" not-null="true" unique="true" />
<property name="KeyName" column="KEY_NAME" type="string" not-null="true" unique="true" />
<property name="CreatedDate" column="CREATION_DATE" type="DateTime" not-null="true" />
<property name="Status" column="STATUS" not-null="true" />
<bag name="QAAuthQuestions" lazy="false" inverse="true" cascade="all-delete-orphan" >
<key column="QA_CLIENT_APP_ID"/>
<one-to-many class="QandADomainModel.QandAAuthenticationQuestion,QandADomainModel"/>
</bag>
</class>

<class name="QandADomainModel.QandAAuthenticationAnswer, QandADomainModel" table="QA_AUTHENTICATION_ANSWERS" >
<id name="Id" column="ANSWER_ID" type="Int32" unsaved-value="0">
<generator class="native"/>
</id>
<property name="Text" column="TEXT" type="string" not-null="true" />
<many-to-one name="User" column="USER_ID" class="QandADomainModel.QandAUser, QandADomainModel" not-null="true" />
<many-to-one name="QAAuthQuestion" column="QUESTION_ID" class="QandADomainModel.QandAAuthenticationQuestion, QandADomainModel" not-null="true" />
<many-to-one name="QAClientApp" column="QA_CLIENT_APP_ID" class="QandADomainModel.QandAClientApplication, QandADomainModel" not-null="true" />
<property name="Status" column="STATUS" type="string" not-null="true" />
<property name="CreatedDate" column="CREATION_DATE" type="DateTime" />
<property name="LastModifiedDate" column="LAST_MODIFICATION_DATE" type="DateTime"/>
</class>
</hibernate-mapping>

michal · **Posted:** Wed Dec 28, 2005 5:58 am

First - I am not a many-to-many guru, but I have several such collections performing well in my apps. If I were you I would try the following:

- try cascade="all" at non-inverse end of collection
- make sure you are adding objects to collection at non-inverse end ( QandAAuthenticationQuestion1.QAUsers.Add(QandAUser1) )
- replace "bag" with "set" - bags are VERY ineffective here (the whole collection must be deleted and recreated in the db with every change)