EntitySet - is there a sane reason that IList.Add doesn't set assigned?
There are 3 ways of adding items to most lists...
- via a direct public API method, typically
Add(SomeType)
- via the generic
IList<T>.Add(T)
interface - via the non-generic
IList.Add(object)
interface method
and you normally expect them to behave more or less the same. However, LINQ's EntitySet<T>
is... peculiar on both 3.5 and 4.0; the IList
API does not flag the set as "assigned" - the other two mechanisms do - this sounds trivial开发者_StackOverflow社区, but it is important in that it heavily influences serialization (i.e. causes it to be skipped) in the boilerplate code.
Example:
EntitySet<string> set1 = new EntitySet<string>();
set1.Add("abc");
Debug.Assert(set1.Count == 1); // pass
Debug.Assert(set1.HasLoadedOrAssignedValues, "direct"); // pass
EntitySet<string> set2 = new EntitySet<string>();
IList<string> typedList = set2;
typedList.Add("abc");
Debug.Assert(set2.Count == 1); // pass
Debug.Assert(set2.HasLoadedOrAssignedValues, "typed list"); // pass
EntitySet<string> set3 = new EntitySet<string>();
IList untypedList = set3;
untypedList.Add("abc");
Debug.Assert(set3.Count == 1); // pass
Debug.Assert(set3.HasLoadedOrAssignedValues, "untyped list"); // FAIL
Now... this is deeply surprising to me; so much so that it took me over 2 hours of tracking upwards through code to isolate what was happening. So...
is there any sane reason for this? Or is this just a bug?
(FWIW, there was also an issue in set.Assign(set)
in 3.5, but this is now fixed in 4.0.)
Interestingly, this has been identified for several versions now (you stated that a 3.5 issue was fixed in 4.0). Here is a post from 2007. The rest of the IList
methods in 4.0 are correctly tied to the IList<T>
methods. I think that there are 2 likely explanations (of the bug/feature variety):
- This is an actual bug that Microsoft has not yet fixed.
- This is a feature that some other Microsoft code is
exploitingleveraging to add items without setting theHasLoadedOrAssignedValues
.
It is probably both - a bug that other code inside the framework is counting on. Sounds like someone said to themselves:
No one is really going to cast this into an IList and then call the Add method, right?
Surprisingly, the difference seems rooted in the fact that the IList.Add
and IList<T>.Add
methods actually have different semantics:
- The
IList.Add
method fails if the entity being added is already present - The
LIst<T>.Add
method removes and then re-adds an entity if is is already present
The apparent reason for this difference is that IList.Add
interface method is defined to return the index of the added entity, which for a typical implementation of IList.Add
will always be the Count
of the collection prior to the Add
.
In any case, because the two implementations are intentionally different, it seems the authors simply accidentally omitted the this.OnModified()
call in the IList.Add
version.
Looks like a bug to me. ILSpy shows the differences between the two implementations:
int IList.Add(object value)
{
TEntity tEntity = value as TEntity;
if (tEntity == null || this.IndexOf(tEntity) >= 0)
{
throw Error.ArgumentOutOfRange("value");
}
this.CheckModify();
int count = this.entities.Count;
this.entities.Add(tEntity);
this.OnAdd(tEntity);
return count;
}
// System.Data.Linq.EntitySet<TEntity>
/// <summary>Adds an entity.</summary>
/// <param name="entity">The entity to add.</param>
public void Add(TEntity entity)
{
if (entity == null)
{
throw Error.ArgumentNull("entity");
}
if (entity != this.onAddEntity)
{
this.CheckModify();
if (!this.entities.Contains(entity))
{
this.OnAdd(entity);
if (this.HasSource)
{
this.removedEntities.Remove(entity);
}
this.entities.Add(entity);
this.OnListChanged(ListChangedType.ItemAdded, this.entities.IndexOf(entity));
}
this.OnModified();
}
}
It looks like the IList implementation simply neglects to call a couple of event invokers (OnListChanged
and OnModified
) that LINQ to SQL probably relies on to track its changes. If this had been intentional, I would have expected them to also leave out the call to OnAdd
.
Why they don't simply have IList.Add
cast the value to TEntity
and call the generic Add
method is beyond me.
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