摘要：
One of the more significant services the DataContext provides is change tracking for entity objects. When
you insert, change, or delete an entity object, the DataContext is monitoring what is happening.
However, no changes are actively being propagated to the database. The changes are cached by the
DataContext until you call the SubmitChanges method.
When you call the SubmitChanges method, the DataContext object’s change processor manages
the update of the database. 阅读全文