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This example shows how to use ODB with C++11. In particular, this example
examines ODB support for the new std::unique_ptr and std::shared_ptr smart
pointers and their lazy variants as well as the unordered containers. It
also shows how to use new C++11 features such as the range-based for-loop
when working with persistent objects and handling query results.
The example consists of the following files:
employee.hxx
Header file defining the 'employee', 'employer', and 'pension_fund'
persistent classes. We use the standard std::shared_ptr/weak_ptr smart
pointers as well as their lazy versions provided by ODB to establish a
bidirectional employee-employer relationship. We also enable session
support for these two classes using the 'db session' pragma. Because
we don't share the 'pension_fund' objects, we use std::unique_ptr
as an object pointer for this persistent class. We also use the
std::unordered_set container to keep track of the employee's email
addresses.
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> --std c++11 --generate-schema --generate-query employee.hxx
Where <database> stands for the database system we are using, for example,
'mysql'.
The --std c++11 option is used to instruct the ODB compiler to compile in
the C++11 mode.
database.hxx
Contains the create_database() function which instantiates the concrete
database class corresponding to the database system we are using. Unlike
other examples, here we use std::unique_ptr instead of std::auto_ptr to
return the created database.
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 creates a number of 'employee', 'employer', and
'pension_fund' objects and persists them in the database. Then the driver
loads and prints some information about various objects and their
relationships. Finally, the driver performs a database query and iterates
over the result printing basic information about the returned objects.
To compile and link the example manually from the command line we can use
the following commands (using MySQL as an example; replace 'c++ -std=c++11'
with your C++ compiler in C++11 mode):
c++ -std=c++11 -c employee-odb.cxx
c++ -std=c++11 -DDATABASE_MYSQL -c driver.cxx
c++ -std=c++11 -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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