5.4 Error Handling

Each predicate in the XSB-DB interface throws an exception with the functor

   xsb_error(database(Number), Message)

where Number is a string with the error number and Message is a string with a slightly detailed error message. It is upto the user to catch this exception and proceed with error handling. This is done by the throw-catch error handling mechanism in XSB. For example, in order to catch the error which will be thrown when the user attempts to close a database connection for a handle (ha) which does not exist:

| ?- catch(db_disconnect(ha),
     xsb_error(database(Number), Message), handler(Number, Message)).

It is the user's responsibility to define the handler predicate which can be as simple as printing out the error number and message or may involve more complicated processing.

A list of error numbers and messages that are thrown by the XSB-DB interface is given below:

• XSB_DBI_001: XSB_DBI ERROR: Driver already registered
  This error is thrown when the user tries to load a driver, using the load_driver predicate, which has already been loaded previously.

• XSB_DBI_002: XSB_DBI ERROR: Driver does not exist
  This error is thrown when the user tries to connect to a database, using db_connect, with a driver which has not been loaded.

• XSB_DBI_003: XSB_DBI ERROR: Function does not exist in this driver
  This error is thrown when the user tries to use a function support for which does not exist in the corresponding driver. For example, this error is generated if the user tries to use db_prepare for a connection established with the mysql driver.

• XSB_DBI_004: XSB_DBI ERROR: No such connection handle
  This error is thrown when the user tries to use a connection handle which has not been created.

• XSB_DBI_005: XSB_DBI ERROR: No such query handle
  This error is thrown when the user tries to use a query handle which has not been created.

• XSB_DBI_006: XSB_DBI ERROR: Connection handle already exists
  This error is thrown when the user tries to create a connection handle in db_connect using a name which already exists as a connection handle.

• XSB_DBI_007: XSB_DBI ERROR: Query handle already exists
  This error is thrown when the user tries to create a query handle, in db_query or db_prepare, using a name which already exists as a query handle for a different query.

• XSB_DBI_008: XSB_DBI ERROR: Not all parameters supplied
  This error is thrown when the user tries to execute a prepared statement, using db_prepare_execute, without supplying values for all the parameters in the statement.

• XSB_DBI_009: XSB_DBI ERROR: Unbound variable in parameter list
  This error is thrown when the user tries to execute a prepared statement, using db_prepare_execute, without binding all the parameters of the statement.