EF4 does not commit Updates

Sorry to ask such a general question: what can cause EF to insert records but not update ?

I face a strange situation where i change an entity and when i call SaveChanges(), the changes are no开发者_运维技巧t committed in the DB. thanks Jon

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Are you keeping the ObjectContext alive for the entire lifetime of your entities? If not, when you re-attach the entities to a new ObjectContext for saving, the changes made may not be reflected and the entities may not be considered dirty.

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Do you have a primary key defined?