An object is being passed like this
- Object gets pull from the database through the Business Logic layer and WCF, as well as getting converted into a detached object.
- Values are changed in the Business Logic Layer.
- Object gets passed back into the WCF for an update.
I've seen several ways of how a detached object could be updated. Previously in the data access layer, I was retrieving the original object from the database and getting the object again by the original's entity key. Then updated the values and applied the changes. It looks something like this:
using (MyDBContext db = new MyDBContext ())
{
My_Object obj = db.GetObjectByKey(GetObjectFromDatabaseByID(id).EntityKey) as My_Object;
obj.Name = <newName>;
if (obj != null)
{
db.ApplyCurrentValues("My_Object_Table_Name", obj);
db.SaveChanges();
return "Succesfully Updated!";
}
else
return "Record Does Not Exist.";
}
So one thing, the method that surrounds this code is only passing an 'id'. There is no objects coming in. Therefore, the object would have to be retrieved again to use its Entity Key to grab the object again, except with an attached state. Another parameter that was passed into the method was the newName. So this newName variable has to be assigned to the new attached object. Only then, we can apply and save the changes. Yes, this is a crude way of doing it, but it works.
Recently, I found a new way of handling an update. So what if we pass in a whole object? Will we have to consider the change of all members of the object? What if the object has 50 members? Well, coding will definitely suck. This method was posted on MSDN, so I'm just going to take it as a valid strategy, and it goes something like this:
EntityKey key = default(EntityKey);
object originalObj = null;
using (MESDataModel.e_MESEntities db = new MESDataModel.e_MESEntities())
{
key = db.CreateEntityKey("KIT_Part", ct);
if (db.TryGetObjectByKey(key, out originalObj))
{
db.ApplyCurrentValues(key.EntitySetName, ct);
db.SaveChanges();
return "Succesfully Updated!";
}
else
{
return "Record Does Not Exist.";
}
}
In this situation, we are creating an entity key out of the passed in object. If it already has a key, then it will return the original instead of creating a new one. Similar to the first method, we are using the key to retrieve an attached object. At this point, the attached object and the passed in object now has the same keys. Call ApplyCurrentValues and the data from the passed in object will write to the attached object within context. This is pretty much MSDN's definition of what ApplyCurrentValues does. Save changes and everything should work. Hope this kind of helps.
Hmm, Okay, what about using DetectChanges?
This method seems to be good, if you are pulling straight from the database, writing new values, and saving it back to the database. No detached objects involved here. If there is a way to use this method with cross platform in mind (Android, iPhone), please let me know.
Hmm, Okay, what about using DetectChanges?
This method seems to be good, if you are pulling straight from the database, writing new values, and saving it back to the database. No detached objects involved here. If there is a way to use this method with cross platform in mind (Android, iPhone), please let me know.
