Error Handling

The simplest kind of error handling is to know whether a method succeeded in its operation or not. This level of error handling is accomplished by looking at the return value of the method. Most methods in the library return a result of type oresult. An oresult will either have the value OSUCCESS, which indicates that the method worked, or OFAILURE, which indicates that some error occurred during the method's execution.

Note: Beginning with this release, newly introduced methods may throw an OException object in the case of an error.

After an error has occurred, you will often want more information about exactly what went wrong. There are two broad categories of problems:

• Errors that occur in the server. These are things like invalid SQL statements, attempting to access records that are locked, and so on.
• Errors occurring in the class library. These are things like improperly initialized objects, invalid arguments, out of memory conditions and so on.

The two categories of problems are reported in different ways.

The Oracle errors are reported through the ServerErrorNumber and GetServerErrorText methods of OSession and ODatabase. Errors that occur when connecting to the database, or in the execution of transaction operations, will be reported through OSession. Errors that occur while processing an SQL statement, for instance when opening a dynaset or using ExecuteSQL, will be reported through ODatabase. The number returned by ServerErrorNumber is a standard Oracle error number. An error number of 0 indicates no error. The text returned by GetServerErrorText is the standard Oracle error message. For more information about Oracle errors consult your Oracle documentation.

The class library errors are reported through the ErrorNumber and GetErrorText methods that are supported by most of the objects (all those that inherit these methods from OOracleObject). Each object will have available the most recent state of that object. The object's error state is cleared at the beginning of executing each method. GetErrorText will not have explanatory text available for all errors.

Because error reporting is done through additional calls rather than through returns of error codes it is possible to obtain error information about the execution of methods that cannot have error return values such as constructors and overloaded assignment operators. After using a constructor, especially a "construct and open" constructor or an assignment operator you should check an object's error state by calling ErrorNumber.

The following table lists all possible error codes returned by ErrorNumber and a brief explanation of each:

Error Codes Returned by ErrorNumber

These values can be found in the oraconst.txt file.

Find Method Parser Errors

Find method parser errors occur when the parser cannot parse the expression (find clause) in a Find method. These errors specify what part of the expression caused the error.

Find Method Parser Errors

Find Method Runtime Errors

Find method runtime errors occur when the system cannot evaluate a find expression. Such errors are rare. When one occurs, the parser might have generated incorrect code.

Find Method Runtime Errors