Defensive Database Programming - Red Gate Software

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Chapter 7: Advanced Use of ConstraintsAssignedToDeveloperID ,Description ,TicketStatus ,DeveloperStatusFROM dbo.Tickets ;GOROLLBACK ;Listing 7-18: No rows in the Tickets table are modified if Justin goes on vacation.If Justin is on vacation we cannot reopen a ticket assigned to him, as verified byListing 7-19.BEGIN TRANSACTION ;GOUPDATE dbo.DevelopersSET DeveloperStatus = 'Vacation'WHERE DeveloperID = 1 ;-- attempt one: just change the ticket's statusUPDATE dbo.TicketsSET TicketStatus = 'Active'WHERE TicketID = 1 ;Msg 547, Level 16, State 0, Line 6The UPDATE statement conflicted with the CHECK constraint"CHK_Tickets_ValidStatuses"-- attempt two: change both Status and DeveloperStatusUPDATE dbo.TicketsSET TicketStatus = 'Active' ,DeveloperStatus = 'Active'WHERE TicketID = 1 ;Msg 547, Level 16, State 0, Line 11The UPDATE statement conflicted with the FOREIGN KEYconstraint "FK_Tickets_Developers_WithStatus".226
Chapter 7: Advanced Use of ConstraintsSELECT *FROM dbo.Tickets-- restoring test data to its original stateROLLBACK ;Listing 7-19: Trying to reopen a ticket assigned to Justin.We have seen how three constraints work together to enforce a rather complex businessrule. Originally, we used an approach that works in the simplest possible way, and thenwe modified it to be more efficient. We have also removed the side effect of changes inDevelopers.DeveloperID column propagating into the Tickets table (and our FKconstraint will prohibit changes that would result in orphaned rows).Let's move on to discuss another case where constraints really shine: inventory systems.Constraints and Rock Solid Inventory SystemsIn the previous example, we used constraints to improve a trigger-based solutiondiscussed in Chapter 4. This next example is completely new and involves an inventorysystem that is used to store the history of changes to an inventory of items. Listing 7-20creates the InventoryLog table, for this purpose.CREATE TABLE dbo.InventoryLog(-- In a real production system-- there would be a foreign key to the Items table.-- We have skipped it to keep the example simple.ItemID INT NOT NULL ,ChangeDate DATETIME NOT NULL ,ChangeQuantity INT NOT NULL ,-- in a highly concurrent system-- this combination of columns-- might not be unique, but let us keep-- the example simple227
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Enforcing Data Integrity in the App
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About the AuthorAlex Kuznetsov has
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IntroductionResilient T-SQL code is
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IntroductionSpecific examples demon
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IntroductionWhat this book does not
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Chapter 1: Basic Defensive Database
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Chapter 5: Reusing T-SQL CodeBEGINS
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Defensive Database Programming - Red Gate Software

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