Defensive Database Programming - Red Gate Software

Chapter 4: When Upgrading Breaks CodeCREATE TABLE dbo.Developers(DeveloperID INT NOT NULL ,FirstName VARCHAR(30) NOT NULL ,Lastname VARCHAR(30) NOT NULL ,Status VARCHAR(10) NOT NULL ,CONSTRAINT PK_Developers PRIMARY KEY (DeveloperID) ,CONSTRAINT CHK_Developers_Status CHECK ( Status IN( 'Active','Vacation' ) )) ;GOCREATE TABLE dbo.Tickets(TicketID INT NOT NULL ,AssignedToDeveloperID INT NULL ,Description VARCHAR(50) NOT NULL ,Status VARCHAR(10) NOT NULL ,CONSTRAINT PK_Tickets PRIMARY KEY ( TicketID ) ,CONSTRAINT FK_Tickets_DevelopersFOREIGN KEY ( AssignedToDeveloperID )REFERENCES dbo.Developers ( DeveloperID ) ,CONSTRAINT CHK_Tickets_StatusCHECK ( Status IN ( 'Active', 'Closed' ) )) ;Listing 4-7: Creating the Developers and Tickets tables.Note that, thanks to our FOREIGN KEY constraint, FK_Tickets_Developers, newlyadded developers cannot have tickets assigned to them. We only need to make sure ourrules are enforced at the point when a developer's status is updated. Therefore, on theDevelopers table, we create an AFTER UPDATE trigger, as shown in Listing 4-8. It isdesigned to make sure that developers cannot go on vacation if they have active ticketsassigned to them.111