C# in Depth

324 CHAPTER 12 LINQ beyond collections-- Generated SQLSELECT [t0].[Summary], [t1].[Name]FROM [dbo].[Defect] AS [t0]LEFT OUTER JOIN [dbo].[DefectUser] AS [t1]ON [t1].[UserID] = [t0].[AssignedToUserID]Of course, if you navigate via more properties, the joins get more and more complicated.I’m not going into the details here—the important thing is that LINQ to SQLhas to do a lot of analysis of the query expression to work out what SQL is required.Before we leave LINQ to SQL, I ought to show you one more feature. It’s part ofwhat you’d expect from any decent ORM system, but leaving it out would just feelwrong. Let’s update some values in our database.12.1.4 Updating the databaseAlthough insertions are straightforward, updates can be handled in a variety of ways,depending on how concurrency is configured. If you’ve done any serious databasework you’ll know that handling conflicts in updates from different users at the sametime is quite hairy—and I’m not going to open that particular can of worms here. I’lljust show you how easy it is to persist a changed entity when there are no conflicts.Let’s change the status of one of our defects, and its assignee, and that person’sname, all in one go. As it happens, I know that the defect with an ID of 1 (as createdon a clean system) is a bug that was created by Tim, and is currently in an “accepted”state, assigned to Darren. We’ll imagine that Darren has now fixed the bug, andassigned it back to Tim. At the same time, Tim has decided he wants to be a bit moreformal, so we’ll change his name to Timothy. Oh, and we should remember to updatethe “last modified” field of the defect too. (In a real system, we’d probably handle thatwith a trigger—in LINQ to SQL we could implement partial methods to set the lastmodified time when any of the other fields changed. For the sake of simplicity here,we’ll do it manually.)Listing 12.5 accomplishes all of this and shows the result—loading it in a freshDataContext to show that it has gone back to the database.Listing 12.5Updating a defect and showing the new detailsusing (var context = new DefectModelDataContext()){context.Log = Console.Out;Defect defect = context.Defects.Where(d => d.ID==1).Single();BFinds defect withextension methodsUser tim = defect.CreatedBy;}defect.AssignedTo = tim;tim.Name = "Timothy Trotter";defect.Status = Status.Fixed;defect.LastModified = SampleData.August(31);context.SubmitChanges();C Updatesentity detailsD Submits changes to databaseLicensed to Rhona Hadida