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, etc.

· 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 via 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 via OSession. Errors that occur while processing an SQL statement, for instance when opening a dynaset or using ExecuteSQL, will be reported via 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 via 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 via 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

Constant	Value	Description
OERROR_NONE	0	No error
OERROR_NOINTER	11	Internal Error
OERROR_MEMORY	12	Couldn't allocate necessary memory.
OERROR_BADERR	13	Internal Error
OERROR_INVPARENT	14	An attempt was made to get an object from an unopened object.
OERROR_SYSTEM	15	Internal Error
OERROR_NOTOPEN	16	An attempt was made to use an unopened object
OERROR_BADARG	17	One of the arguments to the method is invalid.
OERROR_INVRECORD	18	The current record is not valid.
OERROR_ADVISEULINK	4096	Internal error: Invalid advisory connection.
OERROR_POSITION	4098	An attempt was made to retrieve a field value from an empty dynaset.
OERROR_NOFIELDNAME	4099	An invalid field name was specified.
OERROR_TRANSIP	4101	A BeginTransaction was specified while a transaction is already in progress
OERROR_TRANSNIPC	4104	A CommitTransaction was specified without first executing BeginTrans.
OERROR_TRANSNIPR	4105	A Rollback was specified without first executing BeginTrans.
OERROR_NODSET	4106	Internal error: System attempted to destroy non-existent dynaset.
OERROR_INVROWNUM	4108	An attempt was made to reference an invalid row. This will happen when IsEOF or IsBOF is True or when the current row has been deleted and no record movement has occurred.
OERROR_TEMPFILE	4109	An error occurred while trying to create a temporary file for data caching.
OERROR_DUPSESSION	4110	An attempt was made to create a named session that already exists.
OERROR_NOSESSION	4111	Internal error: System attempted to destroy non-existent session.
OERROR_NOOBJECTN	4112	An attempt was made to reference a named object of a collection (other than the fields collection) that does not exist.
OERROR_DUPCONN	4113	Internal error: Duplicate connection name.
OERROR_NOCONN	4114	Internal error: System attempted to destroy non-existent connection.
OERROR_BFINDEX	4115	An invalid field index was specified. The range of indices is 0 to Count -1.
OERROR_CURNREADY	4116	Internal error: System attempted to move to row in invalid dynaset.
OERROR_NOUPDATES	4117	An attempt was made to change the data of a non-updatable dynaset.
OERROR_NOTEDITING	4118	An attempt was made to change a fields value without first executing StartEdit.
OERROR_DATACHANGE	4119	An attempt was made to Edit data in the local cache, but the data on the Oracle server has been changed.
OERROR_NOBUFMEM	4120	Out of memory for data binding buffers.
OERROR_INVBKMRK	4121	An invalid bookmark was specified.
OERROR_BNDVNOEN	4122	Internal error: Bind variable not enabled.
OERROR_DUPPARAM	4123	An attempt was made to create a named parameter using Add, but that name already exists.
OERROR_INVARGVAL	4124	An invalid offset or length parameters was passed to GetChunk or an internal error has occurred using AppendChunk.
OERROR_INVFLDTYPE	4125	An attempt was made to use GetChunk or Append Chunk on a field that was not of the type Long or Long Raw.
OERROR_TRANSFORUP	4127	A SELECT ... FOR UPDATE was specified without first executing BeginTransaction
OERROR_NOTUPFORUP	4128	A SELECT ... FOR UPDATE was specified but the query is non-updatable.
OERROR_TRANSLOCK	4129	A Commit or Rollback was executed while a SELECT ... FOR UPDATE is in progress.
OERROR_CACHEPARM	4130	An invalid cache parameter was specified.
OERROR_FLDRQROWID	4131	An attempt was made to reference a field that requires a ROWID (Long or Long Raw), but the ROWID was not available.
OERROR_OUTOFMEMORY	4132	Internal Error
OERROR_MAXSIZE	4135	Element size specified in AddTable exceeds the maximum allowed size for that variable type. See AddTable Method for more details.
OERROR_INVDIMENSION	4136	Dimension specified in AddTable is invalid (negative). See AddTable Method for more details.
OERROR_MAXBUFFER	4137	Buffer size for parameter array variable exceeds 32512 bytes (OCI limit).
OERROR_ARRAYSIZ	4138	Dimensions of array parameters used in insert/update/delete statements are not equal.
OERROR_ARRAYFAILP	4139	Error processing arrays. For details refer to OO4OERR.LOG in the windows directory.
OERROR_NONBLKINPROGRESS	4153	Non-blocking operation in progress
OERROR_NONONBLKINPROGRESS	4154	Operation is valid only when non-block is in progress

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

Constant	Value	Description
OERROR_STOVER	4496	Stack overflow.
OERROR_SYNTAX	4497	Syntax error
OERROR_MISPLC	4498	Misplaced parenthesis
OERROR_MISQTE	4499	Misplaced quotation marks
OERROR_MISPAR	4500	WARNING: Missing closing parenthesis
OERROR_EXPCTD	4501	Usually open parentheses expected
OERROR_PRSERR	4502	Unknown parser error condition
OERROR_DUMMY	4503	Syntax not supported
OERROR_INVCOL	4504	Invalid column name
OERROR_TOKEN	4505	Maximum token size exceed in token.
OERROR_COLTYPE	4506	Unsupported data type
OERROR_UNXPTD	4507	Unexpected token found.

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

Constant	Value	Description
OERROR_INSTR	4516	Internal error: Invalid instruction
OERROR_STACK	4517	Internal error: Stack over/under-flow
OERROR_CONVERT	4518	Invalid type conversion
OERROR_DATA	4519	Invalid datatype
OERROR_SQLFUNC	4520	SQL function missing argument
OERROR_COMP	4521	Invalid comparison
OERROR_SQLEXEC	4522	Select from dual failed
OERROR_SQLTYPE	4523	Invalid datatype in Select from dual