This example shows how to use polymorphism inheritance with ODB. This inheritance style is normally used to provide polymorphic behavior through a common interface. The base class defines a number of virtual functions and, normally, a virtual destructor while the derived classes provide specific implementations of these virtual functions. The other commonly used inheritance style is reuse inheritance. Refer to the inheritance/reuse example for more information on this style. The example consists of the following files: employee.hxx employee.cxx Header and source files defining the 'person' abstract polymorphic persistent class as well as the 'employee' and 'contractor' concrete persistent classes. employee-odb.hxx employee-odb.ixx employee-odb.cxx employee.sql The first three files contain the database support code and the last file contains the database schema for the employee.hxx header. These files are generated by the ODB compiler from employee.hxx using the following command line: odb -d <database> --generate-schema --generate-query employee.hxx Where <database> stands for the database system we are using, for example, 'mysql'. database.hxx Contains the create_database() function which instantiates the concrete database class corresponding to the database system we are using. driver.cxx Driver for the example. It includes the employee.hxx and employee-odb.hxx headers to gain access to the persistent classes and their database support code. It also includes database.hxx for the create_database() function declaration. In main() the driver first calls create_database() to obtain the database instance. It then persists a number of employee and contractor objects via their common base (person). The next transaction loads these objects, also via their common base. Once loaded, the driver calls the print() virtual function on each of them. Next, the driver changes an employee from temporary to permanent and updates its state in the database, again using the base class interface. The driver then queries the database for all the person objects that have Doe as the last name. The result set of this query contains a mix of employee and contractor objects. The driver iterates over this result set and calls the print() virtual function for each object. Finally, the driver erases the state of the persistent objects from the database, again using the base class interface. To run the example we may first need to create the database schema (for some database systems, such as SQLite, the schema is embedded into the generated code which makes this step unnecessary). Using MySQL as an example, this can be achieved with the following command: mysql --user=odb_test --database=odb_test < employee.sql Here we use 'odb_test' as the database login and also 'odb_test' as the database name. Once the database schema is ready, we can run the example (using MySQL as the database): ./driver --user odb_test --database odb_test