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This example shows how to persist objects that use Qt smart pointers,
containers, and value types with the help of the Qt profile library
(libodb-qt).
The example consists of the following files:
employee.hxx
Header file defining the 'employee' and 'employer' persistent classes.
We use QSharedPointer/QWeakPointer smart pointers provided by Qt (as
well as their lazy versions provided by the Qt profile library) to
establish a bidirectional employee-employer relationship. The QList
type is used to store the collection of employees employed by the
employer. We also use the QDateTime type to store the employee's date
of birth and QString to store the employee's first and last name. A
QSet instance keeps track of the employee's email addresses. Finally
we use QByteArray to store the employee's public key.
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> -p qt --generate-schema --generate-query \
--generate-session employee.hxx
Where <database> stands for the database system we are using, for example,
'mysql'.
The -p option is used to instruct the ODB compiler to load the Qt profile.
The --generate-session option is used to enable session support for all
the persistent classes in employee.hxx.
database.hxx
Contains the createDatabase() 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 createDatabase() function
declaration.
In main() the driver first calls createDatabase() to obtain the database
instance. It then creates a number of 'Employee' and 'Employer' objects and
persists them in the database. The next transaction loads all the employees
of a particular employer using the employee-employer relationship. Finally,
the driver performs a database query which uses data member of the Qt
QString and QDate types in its criterion.
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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