How can I associate application information with a database or database environment handle?
In the C API, the DB and DB_ENV handles each contain an “app_private” field intended to be used to reference application-specific information. See the db_create and db_env_create documentation for more information. In the C++ or Java APIs, the easiest way to associate application-specific data with a handle is to subclass the Db and DbEnv handles, for example subclassing Db to get MyDb. Objects of type MyDb will still have the Berkeley DB API methods available on them, and you can put any extra data or methods you want into the MyDb class. If you are using “callback” APIs that take Db or DbEnv arguments (for example, the Db.set_bt_compare method), these will always be called with the Db or DbEnv objects you create. So if you always use MyDb objects, you will be able to take the first argument to the callback function and cast it to a MyDb (in C++, cast it to (MyDb*)). That will allow you to access your data members or methods.
When using the C API, the DB and DB_ENV handles each contain an app_private field intended to be used to reference application-specific information. See the db_create and db_env_create documentation for more information. In the C++ or Java APIs, the easiest way to associate application-specific data with a handle is to subclass the Db and DbEnv handles, for example subclassing Db to get MyDb. Objects of type MyDb will still have the Berkeley DB API methods available on them, and you can put any extra data or methods you want into the MyDb class. If you are using callback APIs that take Db or DbEnv arguments (for example, the Db.set_bt_compare() method), these will always be called with the Db or DbEnv objects you create. So if you always use MyDb objects, you will be able to take the first argument to the callback function and cast it to a MyDb (in C++, cast it to (MyDb*)). That will allow you to access your data members or methods.
