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This example shows how to use reuse inheritance with ODB. This inheritance
style normally lacks virtual functions and a virtual destructor in the base
class. The application code is normally written in terms of the derived
classes instead of the base.
The other commonly used inheritance style is polymorphism inheritance. Refer
to the inheritance/polymorphism example for more information on this style.
The example consists of the following files:
employee.hxx
Header file defining the 'person' and 'employee' abstract persistent
classes as well as the 'permanent_employee', 'temporary_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 permanent and temporary employee
objects as well as a number of contractor objects. The next transaction
looks up a contractor based on the email address. Finally, the driver
performs a database query which uses a data member from the base class
in its criterion.
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++ -c employee-odb.cxx
c++ -DDATABASE_MYSQL -c driver.cxx
c++ -o driver driver.o employee-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 < 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
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