Indeed, Object-Relational Modeling represents the mapping between the relational database model and the object data model. Further, each table in the database is represented by a class and we formulate queries in the language of programming such as C rather than in SQL. Also, the queries are translated in SQL at runtime. Further, the fields in an entity class represent the columns of the table. Also, all related entity classes have an associated DataContext object which is basically a source of all entities.
Therefore, we create a Windows Forms Application. Further, after creating the application, click on the Project menu and select the Add New Item option. It will open an Object-Relational Designer Editor. Now, you can drag your database table from the Server Explorer to the Object-Relational Designer surface.
Basically, this process creates several entity classes that we will use in our application. However, before we perform any database operation, we must have a DataContext object with us. Therefore, we need to create an object of the DataContext and pass the ConnectionString as a parameter in the constructor.
While, you can also create an object of DataContext without ConnectionString, but then updates are not reflected in the physical database. Find centralized, trusted content and collaborate around the technologies you use most. Connect and share knowledge within a single location that is structured and easy to search. To update data, you need to fetch it out, update the record, and submit the changes:.
In the ExecuteCommand statement, you can send the query directly, with the value for the specific record you want to update. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow.
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Active Oldest Votes. Marc Gravell Marc Gravell k gold badges silver badges bronze badges. So now, if you view the details for the books, you'll see their Category is set to WPF :. Therefore, if you take a book that's in one category and add it to a different category, you are effectively moving it to that new category even though you didn't explicitly ask for this. When we remove a book from a category, our OnBookRemoved delegate clears the Category property from that Book instance. We, for some reason, have two copies of Programming Ruby , so let's remove the Programming Ruby 1.
Finally, we can complete our M:M relationships. These are a little trickier because we want to keep our Join table BookAuthor out of our public interface so callers can work directly with Book s and Author s and not have to care how they're joined together. If you're coding along, then you already added logic into BookAuthor so that if either side updates a BookAuthor relationship, it handles synchronizing both the Book and the Author for you.
What remains is providing a mechanism for users to set a Book 's authors, and an Author 's books. And, we created a public Authors property that serves as a proxy, pulling this book's authors from BookAuthors :. The problem with this approach is we now have no way to tell when a caller adds or removes Author s from our Book. What we need is something akin to the EntityRef delegates for OnAdd and OnRemove so that we can perform our synchronization whenever a caller adds or removes an author.
Since our data is not in an EntryRef, we need another way to get notifications when an author is added or deleted. We can do this by making Authors return an ObservableCollection that will notify us when changes are made to it:. The second line authors. This is the delegate method we registered to be notified of all changes made to our Authors collection.
Create the method to respond to the Add and Remove events, and use its NotifyCollectionChangedEventArgs to gain access to the items that were added e.
NewItems or removed e. OldItems :. If you've been coding along, then you already did this when you added logic to BookAuthor 's set methods for Book to add the new BookAuthor instance to the Book :. The way this works is that when you attach add the BookAuthor instance to your Book , LINQ to SQL notices the change because it's monitoring Book for changes , and so it will automatically insert this attached BookAuthor record into the database the next time you call SubmitChanges.
Voila, a new BookAuthor relationship. Step 1 calls a RemoveRecord method on the DataContext which we'll add below. The reason it does this is because, unlike any of our other changes made so far, deleting a record always requires direct access to a DataContext. But, we don't want to have to pass the DataContext to our entity classes. We can instead handle this with a static method on the DataContext that:. The method uses Generics so that it can take any record. Warning : If you do choose to create a new DataContext instance for RemoveRecord , you'll have to either:.
Finally, update the code for the other side of your M:M relationship. Here is how that will look for Author :.
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