I have two table ABC, CBZ
ABC contains ID as primary key
CBZ contains ParentId and ChildID as composite key

relation between ABC and CBZ is many to many, i have confusion with relationship amongs the mappings, i have given mapping for the two tables as below.

Mapping for Parent Table
<Class name="NodeBase">
<subclass name="MyAssembly.Node, MyAssembly" discriminator-value="0" >
<bag name="Nodes" table="ABC">
<key column="ParentID" />
<many-to-many class="MYAssembly.NodeRelation, MyAssembly" unique="true" />
</bag>
</subclass>
</Class>

Mapping for Child Table
<class name="MyAsembly.NodeRelation, MyAssembly" table="CBZ" >

<property name="GroupName" column="GroupName" type="string" not-null="true" />
<property name="ProjectName" column="ProjectName" type="string" not-null="true" />
<one-to-one name="Node" column="ChildID" class="MyAssembly.NodeBase, MyAssembly" not-null="true" />
</class>

I'm very new at hibernate, but if you have a many-to-many relationship I think you must have three tables, one to ABC, other to CBZ and another auxiliar table which shows the relation between them.

Read the code in hibernate's doc page 206 (pdf version) for see this.

please forgive me, I think I was in Hibernate forum, not in Nhibernate! So, you can't find the code in que page I said to you, but I still think the issue is the same: you will need three tables in the database to model a many to many relationship.

no main i dont want role of third table

What you have described above is a one-to-many relationship. The cbz table only has data to relate to a single parentId. So the Parent (ABC) has many children (CBZ) and the child has one parent. You will also have to read up on composite key mappings in the docs.