You can use the Attach or Detach methods of the ObjectContext to attach or detach objects. It should be noted that Attach will attach the entire object graph. The method cannot determine which objects are new and which already exist in the ObjectContext. Note that when you execute a query on the ObjectContext, the objects that are returned as a result of the query are attached in the ObjectContext. You can attach an object to the ObjectContext by calling any of the following methods on the ObjectContext:
AttachAddObjectAttachToApplyPropertyChanges
But what does Attach and Detach mean here? You use Attach to attach an object to the context. You should use Attach when the entity already exists in the database want the context to know about it without doing a query to locate the entity. When you attach an entity to the ObjectContext using the Attach method, it sets the EntityState of the object being attached to Unchanged...