barcode generator vb.net free Tactics of Error Handling in Software

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Tactics of Error Handling
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Some DBAs recognize the importance of this issue and place error handling in critical positions in their code. The result would be something like the following:
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Create Procedure prInsertLeasedAsset_2 -- Insert leased asset and update total in LeaseSchedule. -- (demonstration of not exactly perfect solution) ( @intEquipmentId int, @intLocationId int, @intStatusId int, @intLeaseId int, @intLeaseScheduleId int, @intOwnerId int, @mnyLease money, @intAcquisitionTypeID int ) As set nocount on begin transaction -- insert asset insert Inventory(EquipmentId, StatusId, LocationId, LeaseId,
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LeaseScheduleId, OwnerId,
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Debugging and Error Handling
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Lease, values ( @intStatusId, @mnyLease, If @@error <> 0 Begin
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AcquisitionTypeID) @intLeaseId, @intAcquisitionTypeID)
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@intEquipmentId, @intLocationId, @intLeaseScheduleId,@intOwnerId,
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Print 'Unexpected error occurred!' Rollback transaction Return 1 End -- update total update LeaseSchedule Set PeriodicTotalAmount = PeriodicTotalAmount + @mnyLease where LeaseId = @intLeaseId If @@error <> 0 Begin Print 'Unexpected error occurred!' Rollback transaction Return 1 End commit transaction return 0
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This kind of solution contains substantial repetition especially if your business logic requires more than two Transact-SQL statements to be implemented. A more elegant solution is to group codes into a generic error handling procedure:
Create Procedure prInsertLeasedAsset_3 -- Insert leased asset and update total in LeaseSchedule. -- (demonstration of not exactly perfect solution) ( @intEquipmentId int, @intLocationId int,
SQL Server 2000 Stored Procedure Programming
@intStatusId int, @intLeaseId int, @intLeaseScheduleId int, @intOwnerId int, @mnyLease money, @intAcquisitionTypeID int ) As set nocount on begin transaction -- insert asset insert Inventory(EquipmentId, StatusId, Lease, values ( @intStatusId, @mnyLease, If @@error <> 0 GOTO ERR_HANDLER -- update total update LeaseSchedule Set PeriodicTotalAmount = PeriodicTotalAmount + @mnyLease where LeaseId = @intLeaseId If @@error <> 0 GOTO ERR_HANDLER commit transaction return 0 ERR_HANDLER: Print 'Unexpected error occurred!' Rollback transaction Return 1 LocationId, LeaseId, AcquisitionTypeID) @intLeaseId, @intAcquisitionTypeID)
LeaseScheduleId, OwnerId, @intEquipmentId, @intLocationId, @intLeaseScheduleId,@intOwnerId,
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Debugging and Error Handling
This is better, but it does not deal with all of the issues that need to be handled. A typical error that beginners in TSQL make is to check the value of a global variable and then try to return or process it. Such an attempt is usually the result of a good intention such as wanting to notify the user of an error that has occurred.
Create Procedure prInsertLeasedAsset_4 -- Insert leased asset and update total in LeaseSchedule. -- (demonstration of not exactly perfect solution) ( @intEquipmentId int, @intLocationId int, @intStatusId int, @intLeaseId int, @intLeaseScheduleId int, @intOwnerId int, @mnyLease money, @intAcquisitionTypeID int ) As set nocount on begin transaction -- insert asset insert Inventory(EquipmentId, StatusId, Lease, values ( @intStatusId, @mnyLease, If @@error <> 0 GOTO ERR_HANDLER -- update total LocationId, LeaseId, AcquisitionTypeID) @intLeaseId, @intAcquisitionTypeID)
LeaseScheduleId, OwnerId, @intEquipmentId, @intLocationId, @intLeaseScheduleId,@intOwnerId,
SQL Server 2000 Stored Procedure Programming
update LeaseSchedule Set PeriodicTotalAmount = PeriodicTotalAmount + @mnyLease where LeaseId = @intLeaseId If @@Error <> 0 GOTO ERR_HANDLER commit transaction return 0 ERR_HANDLER: Print 'Unexpected error occurred: ' + Convert(varchar, @@Error) - this will -- not work, -- as expected Rollback transaction Return @@Error
Although something like this could work in Visual Basic, for example, in this case the stored procedure will return 0 as an error number. SQL Server sets the value of the @@Error variable after each statement. It treats each statement separately, so the value of @@Error is set to 0 subsequently when the If statement is (successfully) executed. Thus the Print statement displays 0 as an error number, and eventually the stored procedure will also return 0.
A Coherent Error Handling Methodology
Let s discuss a single coherent error handling methodology. The fundamental idea is that all SQL statements within a stored procedure should be covered by this error handling solution. Any time an unexpected error occurs, a stored procedure should stop further processing. When the current stored procedure stops processing, so should the stored procedures that called it. The basic feature of this solution is to follow all SQL statements with a statement that reads the contents of the @@Error variable, along with an If statement, which checks whether the previous command completed successfully.
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