Implementing Entity Validation - ASP.NET Dynamic Data - page 257

using (var context = new NorthwindEntities())
{
var order = CreateOrder();
order.OrderStatus = (byte)OrderStatus.Fulfilled;
context.Orders.AddObject(order);
context.SaveChanges();
order.OrderStatus = (byte)OrderStatus.Paid;
var stateEntry = context.ObjectStateManager.GetObjectStateEntry(order);
byte originalStatus = (byte)stateEntry.OriginalValues[“OrderStatus”];
if (originalStatus == (byte)OrderStatus.Fulfilled &&
order.OrderStatus != (byte)OrderStatus.Fulfilled)
{
// We have a problem
}
context.SaveChanges();
}
In this new version, the code first calls the GetObjectStateEntry method of the
ObjectStateManager to retrieve an ObjectStateEntry , which allows accessing original
property values of the entity via its OriginalValues property. This property returns an
object of type DbDataRecord defined in the System.Data namespace by the ADO.NET
framework. You can use its indexer to access the original property values by name. Having
retrieved the original value of the OrderStatus property, you can compare it against the
current value in the entity object itself.
Accessing Original Property Values in Validation Methods
Out of the box, validation methods, whether they are defined by applying the
CustomValidationAttribute or implementing the IValidatableObject interface, do
not have access to the ObjectStateEntry , the ObjectStateManager , or even the
ObjectContext for that matter. To access the original property values inside the validation
methods, this information needs to be supplied to them by the Validate method of the
UnleashedObjectContext class. Luckily, ValidationContext (which all validation methods
can receive as a parameter) defines the Items property of type IDictionary<object,
object> specifically for that purpose.
Here is how the Validate method in the UnleashedObjectContext was modified to create
the Items dictionary and place an ObjectStateEntry instance in it for the validation
methods to find:
private void Validate(ObjectStateEntry stateEntry)
{
object entity = stateEntry.Entity;
var items = new Dictionary<object, object>();
items[typeof(ObjectStateEntry)] = stateEntry;