Implementing a Many-to-Many Mapping

Many-to-many mappings represent relationships between a collection of source objects and a collection of target objects. In the advanced tutorial, the projects attribute uses a many-to-many-mapping (for example, many employees can have many projects).

To map a many-to-many mapping:

1. Expand the Employee descriptor in the Navigator pane.

2. Click the projects attribute of the Employee descriptor.

3. 
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   Click the Many-to-many Mapping button on the mapping toolbar.

4. Use the Reference Descriptor drop-down list to choose the BaseProject descriptor.

5. Use the Relation Table drop-down list to choose the PROJ_EMP table (the class to map to).

6. Ensure that the Use Indirection field is selected. See "Implementing Indirection in the Tutorial".

   Figure B-41 Many-to-Many Mapping General Tab

   
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7. Click the Source Reference tab, and add a new reference by clicking the New button.

   • Create a new reference named PROJ_EMP_EMPLOYEE, with a source table of PROJE_EMP and target table of EMPLOYEE, and click OK.

   • In the Table Reference drop-down list, choose the PROJ_EMP_EMPLOYEE reference.

   • Click the Add button on the Source Reference tab to add a foreign key relationship.

   • Set the Foreign Key field to EMP_ID (from the PROJ_EMP table).

   • Set the Primary Key field to EMP_ID (from the EMPLOYEE table).

8. Click the Target Reference tab, and add a new reference by clicking the New button.

   • In the Table Reference drop-down list, choose the PROJ_EMP_PROJECT reference.

   • Click the Add button on the Source Reference tab to add a foreign key relationship.

   • Set the Source Field field to PROJ_ID (from the PROJ_EMP table).

   • Set the Target Field field to PROJ_ID (from the PROJECT table).

9. 
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   Click Save on the toolbar or choose File >  Save Project to save the project.