Meet in the Middle: Manually Mapping Classes to Tables

If you have an existing OOM and PDM, you can define mappings between them manually using the Mapping Editor.

1. In the OOM, select Model > Data Sources to open the corresponding list.
2. Click the Add a row tool to create a data source.

   You can create multiple data sources in the model.

3. Double-click the data source in the list to open its property sheet.
4. On the Models tab, click the Add Models tool to select one or more PDMs from the available open PDM as source models for the data source.
   
   
   
5. Define mappings using the Mapping tab or the Mapping Editor.

   The Mapping Editor is more convenient to use as you can define all the mappings in one place just by some drag and drop actions. However, it is easy to understand the correspondence between OOM elements and PDM elements by using the Mapping tab in objects property sheet. So we will introduce you how to use Mapping definition tab to define mappings in the following sections.

   When you are familiar with O/R Mapping concepts, you can use the Mapping Editor.

• Entity Class Mapping
  In order to define mapping for entity classes, you have to:
• Attribute Mapping
  After you have defined class mapping, you can define attribute mappings for the class in the Attributes Mapping sub-tab of the Mapping tab. PowerDesigner will generate some attribute mappings by matching their names with the column names. Click the Add Mappings tool and select the attributes you want to be mapped from the list.
• Primary Identifier Mapping
  Columns of primary keys should be mapped to persistent attributes. Like primary keys for tables, you need to set these persistent attributes as primary identifiers of entity classes. The mapped primary keys should be primary keys of primary tables.
• Association Mapping
  You can define association mapping in the Mapping tab of the association property sheet and select the Add Objects tool to add mapping sources.
• Defining Inheritance Mapping
  Inheritance can be mapped using a table per class, joined subclass, or table per class hierarchy inheritance mapping strategy. You can apply any of these inheritance mapping strategies or mix them. You should define primary identifier on the entity class that is the root of the entity hierarchy.