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diff --git a/odb-examples/view/README b/odb-examples/view/README new file mode 100644 index 0000000..176521f --- /dev/null +++ b/odb-examples/view/README @@ -0,0 +1,73 @@ +This example shows how to define and use views in ODB. It includes views +that show how to load a subset of data members from objects or columns +from tables, perform aggregate queries, and join multiple objects and +tables using object relationships and custom join conditions. + +The example consists of the following files: + +employee.hxx + Header file defining the 'country', 'employer', and 'employee' persistent + classes. The example also uses the "legacy" 'employee_extra' table that is + not mapped to a persistent class. + + After the persistent classes, this header defines a number of views that + show how to obtain various information from the above object model. + +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 --std c++11 -d <database> --generate-schema --generate-query \ + --default-pointer std::shared_ptr --generate-session employee.hxx + + Where <database> stands for the database system we are using, for example, + 'pgsql'. + + The --default-pointer option is used to make std::shared_ptr the default + object pointer. The --generate-session option is used to enable session + support for all the objects which is required to use object loading views. + +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 views as well as + 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 the legacy 'employee_extra' table and proceeds + to populate the database with a number of 'country', 'employer', and + 'employee' objects. Once this is done, the driver uses views defined in + employee.hxx to load and print various information about the object model. + +To compile and link the example manually from the command line we can use the +following commands (using PostgreSQL as an example; replace 'c++' with your +C++ compiler name): + +c++ -c employee-odb.cxx +c++ -DDATABASE_PGSQL -c driver.cxx +c++ -o driver driver.o employee-odb.o -lodb-pgsql -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 PostgreSQL as an example, this +can be achieved with the following command: + +psql --username=odb_test --dbname=odb_test -f 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 PostgreSQL as +the database): + +./driver --user odb_test --database odb_test |