WCF: how to modify registers with different types of operations (update, add, delete...)

Question

Well, in this post, I get to the conclusion that is better to work with services in per call mode, because it's more efficient. This makes me to have data context with a short life, the life of the method that I call.

In this example, I see how to modify data of a list of elements, only is needed to set the state of the entity to modified.

However, how could I do with one operation, modifies and updates, for example?

One case can be this. I have books and authors, and the client application have a view with two datagrids, one for authors and other for books. The user can add authors and modify their information in the first datagrid and do the same with the books in the second datagrid. Also can assign books to their authors.

I have the POCO classes, so I have a author class with a property that is a list of books. Well, I can add books to this list, and then when I call the service method updateAuthors, I only need to use the class of author as parameter, EF knows what to do with the books. It is not needed to pass the book too.

But what happens when in the list of books there are new books and also books that exists but its information is modified?

In the example of the post that I mention in the beginning it says how to do it when all the entity are modify, but if I want to add new registers, I need to set the state to add. So if there is mixed entities, how can I do it? does it exist any pattern or a some way to do this? I have to set the state of all the books? I can know the state of the books, because I use an autonumeric as ID, so if the ID is 0 is a new register, in other case is a modification.

Thanks. Daimroc.

EDIT: Perhaps I don't be very clear in my question. What I want to know is how I can save the changes of many entities at once. For example, I have the Authors, Books and Custormers. I Add, modify and delete information of many of them. In my WCF client I have method to save changes of Authors, other method to save changes of books and other method to save changes of Customers.

How my service is per call, I need to make three calls, one for each type of entities, and this are independents. However, if I use directly entity framework, I can do many changes to many type of entities and I only need to call savechanges once, it make all the work. How can I do the same with WCF and POCO entities?

I am reading about self tracking entities, buy I have the same problem, I can use Applychanges(entity) but if I am not wrong, it applies changes only to one entity. do I need to call N times if I did changes to many entities?

Thanks.

Answer 1

Not sure if this will answer your question, but here is my suggestion:

• Manage the state on your POCO entities by using flags (IsNew, IsDirty, IsDeleted);
• When you pass the POCO entities to the object context, use the ObjectStateManager to change the attached entity state;
• Recursively loop through the list of children entities and apply the same approach.

EDIT: The following code is the AuthorStateManager class:

public partial class AuthorStateManager : IStateManager<Author, Context>
{

    private IStateManager<Book, Context> _BookStateManager = new BookStateManager();

    public void ChangeState(Author m, Context ctx)
    {
        if (m == null) return;
        ctx.Authors.Attach(m);
        if (m.IsDeleted)
        {
            ctx.ObjectStateManager.ChangeObjectState(m, System.Data.EntityState.Deleted);
        }
        else
        {
            if (m.IsNew)
            {
                ctx.ObjectStateManager.ChangeObjectState(m, System.Data.EntityState.Added);
            }
            else
            {
                if (m.IsDirty)
                {
                    ctx.ObjectStateManager.ChangeObjectState(m, System.Data.EntityState.Modified);
                }
            }
        }
        SetRelationsState(m, ctx);
    }

    private void SetRelationsState(Author m, Context ctx)
    {
        foreach (Book varBook in m.Books)
        {
            _BookStateManager.ChangeState(varBook, ctx);
        }
    }
}

where Authors is the ObjectSet, m is a POCO entity of type Author, ctx is the object context, and SetRelationsState is the method that loops through all the children state managers to update their state.

After changing the state, in my repository object I call ctx.SaveChanges(). This is the Update method in AuthorRepository class:

public Author Update(Author m, bool commit)
{
    _AuthorStateManager.ChangeState(m, _ctx);
    if (commit)
    {
        _ctx.SaveChanges();
    }
    return m;
}

_BookStateManager is a private member of BookStateManager type which modifies the Book state in its own ChangeState() method. I suggest you make the State Manager classes implement an interface called IStateManager, which has the ChangeState() method.

It seems a bit convoluted, but it gets easier if you generate code for these classes.

Answer 2

If you want to perform multiple actions in a single service call, then the action to take need to move from being a method call to an object. For example, you might have a InsertCustomerAction class which has a Customer instance tied to it. All of these actions would have a base class (Action) and your WCF method would take in a collection of Action instances.