Exception handling
Torque converts all Exceptions thrown by the Database into
instances of org.apache.torque.TorqueException
or subclasses thereof. TorqueException is a checked exception.
Subclasses of TorqueException whcih are generated by database exceptions
are:
-
org.apache.torque.ConstraintViolationException
- thrown whenever a write operation violates a unique key,
a not-null constraint or a foreign key constraint in the database.
-
org.apache.torque.DeadlockEception
- thrown whenever the database detects a deadlock between two
or more transaction which are executed simultaneously (Note: hsqldb
does not seem to be able to detect deadlocks as of version 2.2.8).
All other database exceptions are mapped to TorqueException directly.
Torque also can throw TorqueExceptions or subclasses thereof
without a database error, e.g. if a database is accessed via Torque
when Torque is not initialized.
Subclasses of TorqueExceptions thrown in special situations are:
-
org.apache.torque.NoRowsException
- thrown whenever a read operation expects to hit exactly one record
but does not hit one (e.g. the generated retrieveByPk methods
in the generated peer classes).
-
org.apache.torque.TooManyRowsException
- thrown whenever a read operation expects to hit at most one record
but does hit more than one (e.g. by the doSelectSingleRecord methods
in the peer classes).