Get the "indexOf" of an ICollection in Entity Framework

I have two objects that are connected in a way such that ObjectA contains an ICollection of ObjectB. I would like to be able to determine the indexOf ObjectB in inside the ICollection<ObjectB> that is stored in ObjectA.

One of the solutions was to convert the ICollection to a list and then use the built in IndexOf. However, when multiple threads access the ICollection, in many cases, I can get the same indexOf value for multiple ObjectBs.

Question Is there any way to have a certain field (of type int) that stores the index of ObjectB inside the ICollection? If not, is there anyway to ensure that indexOf (when multiple threads attempt to access it) gives the right index (i.e. no matter of the thread)?

Possible solutions I've tried to ensure to use a new context for each look up as well as GetDatabaseValues() and Reload(). This has worked better (especially in Debug mode), but when the debug mode is turned off, the same index of value is given to more ObjectBs.

via Chebli Mohamed