solutions
:: Error handling
Error handling
As ABEL is dealing with I/O and databases, a runtime error may happen at any time.
ABEL will inform you of an error by setting the
- Before invoking a library command.
- After a transaction commit.
- After iterating over the result of a read-only query.
ABEL maps database specific error messages to its own representation for errors, which is a hierarchy of classes rooted at
- CONNECTION_SETUP_ERROR: No internet link, or a deleted serialization file.
- AUTHORIZATION_ERROR: Usually a wrong password.
- BACKEND_ERROR: An unrecoverable error in the storage backend, e.g. a disk failure.
- INTERNAL_ERROR: Any error happening inside ABEL.
- PS_OPERATION_ERROR: For invalid operations, e.g. no access rights to a table.
- TRANSACTION_ABORTED_ERROR: A conflict between two transactions.
- MESSAGE_NOT_UNDERSTOOD_ERROR: Malformed SQL or JSON statements.
- INTEGRITY_CONSTRAINT_VIOLATION_ERROR: The operation violates an integrity constraint in the database.
- EXTERNAL_ROUTINE_ERROR: An SQL routine or triggered action has failed.
- VERSION_MISMATCH: The stored version of an object isn't compatible any more to the current type.
For your convenience, there is a visitor pattern for all ABEL error types. You can just implement the appropriate functions and use it for your error handling code.
class
MY_PRIVATE_VISITOR
inherit
PS_DEFAULT_ERROR_VISITOR
redefine
visit_transaction_aborted_error,
visit_connection_setup_error
end
feature -- Visitor features
visit_transaction_aborted_error (transaction_aborted_error: PS_TRANSACTION_ABORTED_ERROR)
-- Visit a transaction aborted error
do
print ("Transaction aborted")
end
visit_connection_setup_error (connection_setup_error: PS_CONNECTION_SETUP_ERROR)
-- Visit a connection setup error
do
print ("Wrong login")
end
end