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Refreshing Cached Data

As discussed throughout this book, Enterprise Objects is essentially a big cache of objects. There are mechanisms within Enterprise Objects to preserve the integrity of its objects and mechanisms to improve performance when dealing with potentially large caches of objects. When you fetch data in an Enterprise Objects application, Enterprise Objects prefers to use data that’s already been fetched (cached data) rather than perform a round trip to the database. The degree to which Enterprise Objects prefers cached data is controlled by many things including an editing context’s fetch timestamp. This is discussed in “Ensuring Fresh Data.”

In the context of managing the object graph, there are scenarios in which you want to refresh the data in the object graph. You can refresh an entire object graph using the methods invalidateAllObjects and invalidateObjectsWithGlobalIDs on EOEditingContext as described in “Discarding Cached Objects,” but you often want to refresh the data in a specific object or objects.

By default, when you refetch data, Enterprise Objects does not update the data in enterprise object instances with the refetched data from the database. This is the default behavior that helps maintain an internally consistent view of the application’s data. However, this is not always the behavior you want, especially if you are more concerned with ensuring the freshness of data than anything else (which is especially true in read-only applications).

To override the default behavior, invoke the method setRefreshesRefetchedObjects on an EOFetchSpecification. Then, when you refetch data, the data in enterprise object instances is refreshed with the refreshed data from the database. (You can refetch the data for a particular enterprise object by invoking on it the method refreshObject. If you need to refresh a set of enterprise objects, use a fetch specification.)

By default setRefreshesRefetchedObjects refreshes only the objects you are refetching. For example, if you refetch Employee objects, you don’t also refetch the Employees’ departments. However, by invoking setPrefetchingRelationshipKeyPaths on a fetch specification, the refetch is also propagated for all of the fetched object’s relationships that you specify in that invocation.

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