This examples shows how to customize the mapping between C++ value types and database types. The example changes the default mapping for the 'bool' type which is now stored in the database as the "true" or "false" string. It also maps the user-defined 'date' type to a suitable database date type. The example consists of the following files: person.hxx Header file defining the 'date' value type and the 'person' persistent class. It also uses the ODB value type pragma to map 'bool' to the 'VARCHAR(5)' database type and 'date' to the 'DATE' database type. traits.hxx traits-mysql.hxx traits-sqlite.hxx ODB 'value_traits' template specializations for the 'bool' and 'date' types. These specializations implement conversion between these types and their database counterparts. person-odb.hxx person-odb.ixx person-odb.cxx person.sql The first three files contain the database support code and the last file contains the database schema for the person.hxx header. These files are generated by the ODB compiler from person.hxx using the following command line: odb -d <database> --generate-query --generate-schema \ --hxx-prologue "#include \"traits.hxx\"" person.hxx Where <database> stands for the database system we are using, for example, 'mysql'. The --hxx-prologue option included the traits.hxx header at the beginning of the generated person-odb.hxx file. This makes the 'value_traits' specializations defined in traits.hxx known to the generated database support code. 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 person.hxx and person-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 'person' objects in the database and executes a query to find objects matching certain criteria. To compile and link the example manually from the command line we can use the following commands (using MySQL as an example; replace 'c++' with your C++ compiler name): c++ -DDATABASE_MYSQL -c person-odb.cxx c++ -DDATABASE_MYSQL -c driver.cxx c++ -o driver driver.o person-odb.o -lodb-mysql -lodb 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 < person.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