EJB representing optional relationship

Hi,
I was wondering how does EJB 2.0 deployment descriptor handles the 1 to 1/0 relationship between 2 entites. For example, 1 course can have 0 or 1 textbook. In this case, textbook is optional and might be represented as null in the database.
The following represents 1-to-many relationship, how can I define 1-to-1/0 relationship? Please help. Thanks.
<relationships>
   <ejb-relation>
      <ejb-relation-name>Textbook-Course</ejb-relation-name>
      <ejb-relationship-role>
         <ejb-relationship-role-name>Textbook-has-Course</ejb-relationship-role-name>
         <multiplicity>many</multiplicity>
         <relationship-role-source>
            <ejb-name>TextbookBean</ejb-name>
         </relationship-role-source>
         <cmr-field>
            <cmr-field-name>course</cmr-field-name>
         </cmr-field>
      </ejb-relationship-role>
      <ejb-relationship-role>
         <ejb-relationship-role-name>Course-has-Textbook</ejb-relationship-role-name>
         <multiplicity>one</multiplicity>
         <relationship-role-source>
            <ejb-name>CourseBean</ejb-name>
         </relationship-role-source>
         <cmr-field>
            <cmr-field-name>textbooks</cmr-field-name>
            <cmr-field-type>java.util.Collection</cmr-field-type>
         </cmr-field>
      </ejb-relationship-role>
   </ejb-relation>
</relationships>

hi,
I think you can use 1-1 relation for your case. It will also take care of 1-0.
You just need to update the Textbook-Course multiplicity tag.
Set multiplicityto one
If there is no textbook in a course the Collection will be empty. if you strictly want to model 1 -1/0 , then no need to using Collection in following tag. Just use the type of TextBookbean's remote interface.
<cmr-field>
<cmr-field-name>textbooks</cmr-field-name>
<cmr-field-type>java.util.Collection</cmr-field-type>
</cmr-field>I am using the same technique in our application . We take help of model 1-1 for 1-0 type of relation.
regards,
Amit

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EJB
v Navigating from a Product to its parent Products results in getParents() method in Product
§ Since a Product can have many parents the return type of getParents() method is
java.util.Collection
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Product and the other Product as parent
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children Products
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Product and other Product as child
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Product and the other Product as child
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Ø DataBase
v For a many-to-many relationship define a new associative (join) table
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Child_Product_ID
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v Example: Product, Parent_Child_Product
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v ejb-jar.xml
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o Source
§ Example:
<relationship-role-source>
<ejb-name>Product</ejb-name>
</relationship-role-source>
o Role name
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ejb-relationship-role-name>
o Multiplicity
§ Example: <multiplicity>many</multiplicity>
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§ Example:
<cmr-field>
<cmr-field-name>children</cmr-field-name>
<cmr-field-type>java.util.Collection</cmr-field-type>
</cmr-field>
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o Source
§ Example:
<relationship-role-source>
<ejb-name>Product</ejb-name>
</relationship-role-source>
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§ Example: <ejb-relationship-role-name>many-Product@parents-Have-Product</
ejb-relationship-role-name>
o Multiplicity
§ Example: <multiplicity>many</multiplicity>
o CMR field
§ Example:
<cmr-field>
<cmr-field-name>parents</cmr-field-name>
<cmr-field-type>java.util.Collection</cmr-field-type>
</cmr-field>
v weblogic-ejb-jar.xml
v weblogic-cmp-rdbms-jar.xml
§ Within <weblogic-rdbms-jar>.<weblogic-rdbms-relation> specify the following:.23
· Name of the relationship matching the name in ejb-jar
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relationship-role-name>
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<relationship-role-map>
<column-map>
<foreign-key-column>Parent_Product_ID</foreign-key-column>
<key-column>Product_ID</key-column>
</column-map>
</relationship-role-map>
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relationship-role-name>
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<relationship-role-map>
<column-map>
<foreign-key-column>Child_Product_ID</foreign-key-column>
<key-column>Product_ID</key-column>
</column-map>
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"Thomas A. Valletta" <[email protected]> wrote in message news:[email protected]...
I am attempting to create an EJB that uses Container Managed Persistence,
but my situation seems to be an odd one. The EJB needs to have a
Many-to-Many relationship to itself, because the object is Hierarchical.
Because this is my first EJB I am having a hard time with all of the
deployment descriptors.
I am asking for an example of any Many-to-Many EJB relationship that uses
Weblogic's built-in link table creation to make the relationship (that
works). I realize that there are confidentiality issues with many people
releasing code. I will make any promise (short of selling my soul) that the
code will be safe and promply destroyed immediately after inspection.
Thanks for any help,
Tom
[email protected]
[att1.html]
[ejb-jar.xml]
[weblogic-cmp-rdbms-jar.xml]
[weblogic-ejb-jar.xml]
[ProductBean.java]
[ProductLocal.java]
[ProductLocalHome.java]

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EJB representing optional relationship

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