In the previous chapter you learned how to add new entities and change or delete existing entities. All the examples we looked at involved making changes one at a time to entities that are tracked by the context. Each of the changes affected a single entity or relationship. You saw that you can perform multiple of these single entity operations and then call SaveChanges to push all the changes to the database in a single transaction. In this chapter we will look at making changes to entities that are not being tracked by a context. Entities that are not being tracked by a context are known as disconnected entities.

For most single-tier applications, where the user interface and database access layers run in the same application process, you will probably just be performing operations on entities that are being tracked by a context. Operations on disconnected entities are much more common in N-Tier applications. N-Tier applications involve fetching some data on a server and returning it, over the network, to a client machine. The client application then manipulates this data before returning it to the server to be persisted.

The N-Tier pattern makes data access more complex because there is no longer a context tracking changes that are made to each entity. The data is fetched using one context, and returned to the client where there is no context to track changes. The data is then sent back to the server and must be persisted back to the database using a new instance of the context.

When it comes time to persist the data on the server, you are typically working with a graph of entities. A graph of entities is simply a number of entities that reference each other. We’ve already worked with graphs of entities that are attached to the context. In the last chapter we looked at adding a relationship using a navigation property, which is enough to create a graph, because one entity now references another. In N-Tier scenarios this graph of entities is usually disconnected from the context, though, meaning the context isn’t yet tracking any of the entities in the graph.

When it comes time to start performing operations on this disconnected graph, there are some additional behaviors in Entity Framework that you need to be aware of. The entity that you perform the operation on is known as the root of the graph. Performing an operation on the root of disconnected graph can have side effects on the rest of the graph, too.