The NHibernate designer supports inheritance hierarchies of entities. To specify that one entity derives from another, either:
- Select the derived entity, go to the Properties window, and change the Base Class setting to the desired base class; or
- Open the Toolbox, select the Inheritance tool, and drag an arrow from the derived entity to the base entity.
The NHibernate designer currently supports only table per hierarchy inheritance, also known as single table inheritance. In this mapping, all entities in the hierarchy are mapped to a single table, which contains columns for every property defined at any level of the hierarchy. NHibernate determines what type of entity a given row represents using a discriminator. For example, a hierarchy representing different kinds of employee might use an EmployeeType column as a discriminator.
To specify which column is the discriminator, select the base entity, go to the Properties window and enter the column in the Discriminator setting. You must also specify what discriminator value maps to the base class: null or not null.
To specify the discriminator value that identifies each derived class, select the inheritance arrow, go to the Properties window, and enter the value against the Discriminator Value setting.
