Article link: RIA Services and Validation

RIA Services and Validation by Nikhil
Excerpt:

public void CommitEditing() {
    if (IsEditing == false) {
        return;
    }

    if (SelectedBook.Validate(_bookShelfContext.ValidationContext) == false) {
        return;
    }

    if (SelectedBook.IsNew) {
        _bookShelfContext.BookExists(SelectedBook.ASIN,
            delegate(InvokeOperation<bool> operation) {
                if (operation.Value) {
                    ValidationResult duplicateError =
                        new ValidationResult("This book already exists in the book club.",
                                             new string[] { "Title" });
                    SelectedBook.ValidationErrors.Add(duplicateError);
                }
                else {
                    EndEditing();
                }
            }, null);
    }
    else {
        EndEditing();
    }
}