Multiple ObjectStateManager errors when attempting to update an Entity in Entity Framework

Multiple ObjectStateManager errors when attempting to update an Entity in
Entity Framework

This is a problem that has been cropping up for months and is proving to
be extremely frustrating.
I have an entity ... StorageContract ... which inherits from Contract;
created from a TPT (Table per Type) relationship (I am not sure if that
makes a difference). When I attempt to update an existing StorageContract
by passing an updated definition of the contract to the Update method ...
public StorageContract UpdateStorageContract(StorageContract contract)
{
Context.ObjectContext.ApplyCurrentValues("Contracts", contract);
Context.SaveChanges();
return contract;
}
... I get the error ...
"An object with a key that matches the key of the supplied object could
not be found in the ObjectStateManager"
I found the following post ... "An object with a key that matches the key
of the supplied object could not be found in the ObjectStateManager" ...
which led me to try "attaching" the contract parameter.
public StorageContract UpdateStorageContract(StorageContract contract)
{
Context.ObjectContext.AttachTo("Contracts", contract);
Context.SaveChanges();
return contract;
}
... Which results in an error that seems to be confusingly quite the
opposite of the previous error ...
"An object with the same key already exists in the ObjectStateManager. The
ObjectStateManager cannot track multiple objects with the same key"
The first error indicated that the entity could not be updated because it
could NOT be found ... where as this one seems to suggest that it cannot
be updated because it already exists(??). Anyway that led me to the
following post ... "An object with the same key already exists in the
ObjectStateManager. The ObjectStateManager cannot track multiple objects
with the same key". SO I reworked the code again based on that ...
public StorageContract UpdateStorageContract(StorageContract contract)
{
var origEntry = Context.Entry<StorageContract>(contract);
if (origEntry.State == System.Data.EntityState.Detached)
{
var set = Context.Set<StorageContract>();
StorageContract attachedEntity = set.Find(contract.Id);
if (attachedEntity != null)
{
var attachedEntry = Context.Entry(attachedEntity);
attachedEntry.CurrentValues.SetValues(contract);
}
else
{
origEntry.State = System.Data.EntityState.Modified;
}
}
Context.SaveChanges();
return contract;
}
Which results in the same error ...
"An object with the same key already exists in the ObjectStateManager. The
ObjectStateManager cannot track multiple objects with the same key"
I am chasing this down a rabbit hole that caves in at every turn! I am
desperate for help with this!!
Thanks!