Update in linq c

If you want to delete a row in a table that has constraints against it, you must either set the ON DELETE CASCADE rule in the foreign-key constraint in the database, or use your own code to first delete the child objects that prevent the parent object from being deleted. Otherwise, an exception is thrown. The following excerpts use the Customer and Order classes from the Northwind sample database.

Class definitions are not shown for brevity. You can override this behavior by using your own custom logic, typically by way of a stored procedure. Developers using Visual Studio can use the Object Relational Designer to develop stored procedures for this purpose. Therefore, you need to add logic to your classes so they know how to update their relationships themselves. In our M:1 classes, we want to be able to traverse the object model from both directions. For example, each Book should contain an instance of the Category it belongs to, and each Category should contain a collection of its Book s:.

Imagine you notice that the book C in Depth 's category has been set to Java and you want to fix it. When you update C in Depth to the category C , three things should happen:. LINQ to SQL will handle step 1 for you when you call SubmitChanges , but your classes are responsible for updating the other side of their relationship steps 2 and 3.

But, and this is the tricky part, we're going to be instructing each side of the relationship to inform the other side when it's updated. So, we need to add some additional checks to this method to prevent it from looping:. There are two ways to view this relationship in our classes:. In our Book Catalog application, a book can only belong to a single category, so when we update the book's category, it should get automatically moved from the LINQ category to the C one.

To do this, retrieve both books from the DataContext and set their Category to the C category. Then, call SubmitChanges to persist the changes to the database. Even though only the Book objects were updated, the synchronization code we added caused the Category objects to be updated as well:. Now, let's synchronize the M:1 relationships in our M:M Join tables.

Whenever we have a M:M Join table, as we do with BookAuthors , the join table is, of course, just two M:1 relationships, so we can mirror what we did for Book. We want our Join tables to provide a central location for ensuring both sides of the M:M relationship are kept synchronized. So, regardless of whether someone updates a Book to have a new author, or if they update an Author to add that person's books - the central class BookAuthor will ensure both sides are synchronized accordingly.

In our example, we'll update BookAuthor 's set method for Author just like we updated Book. Category 's set :. We can't see this in action just yet. First, we have to see how to handle the other side of our M:M relationships: the 1:M relationship. Just as we can update a Book 's category and have it automatically synchronize the old and the new Category for us, we should be able to add or remove books from a Category and have them update the Book instances accordingly.

Here's the cool part. And, EntitySet s let you specify delegates to be called whenever an item is added to or removed from its collection. So, create two delegate methods to handle this synchronization:. Then, construct the EntitySet by passing in these two delegate methods. Since the methods are instance methods, you'll need to do this in Category 's constructor:.

To demonstrate adding new 1:M relationships, add a couple of new books without a category. Notice that we never set the Category on the books directly, but the synchronization code we added takes care of that for us. Error dotnet swagger tofile --serializeasv2 --output mysql executeScalar only if successful asp. NET and C? How to use the protected keyword in C c printwindow how to change the extension of a file C button size xamarin how to loop over array in c windows forms webbrowser navigate c get random integer how to count letters in c force overwrite c c write line variable c how to get connection string from app config list of vectors c HMD Motion Emulation check if string is a guid c c object to dictionary vb.

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