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diff --git a/odb-examples/mapping/README b/odb-examples/mapping/README new file mode 100644 index 0000000..48bbe4f --- /dev/null +++ b/odb-examples/mapping/README @@ -0,0 +1,79 @@ +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 +traits-pgsql.hxx +traits-oracle.hxx +traits-mssql.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 --std c++11 -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, + 'pgsql'. + + 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 PostgreSQL as an example; replace 'c++' with your +C++ compiler name): + +c++ -DDATABASE_PGSQL -c person-odb.cxx +c++ -DDATABASE_PGSQL -c driver.cxx +c++ -o driver driver.o person-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 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 PostgreSQL as +the database): + +./driver --user odb_test --database odb_test |