No Tracking With Entity Framework Core

DbContext in Entity Framework is responsible for tracking the changes made on the entity or object, so the correct update is done to the database when the SaveChange() method of context is called. When we retrieve entities using an object query, the Entity Framework puts these entities in a cache and tracks whatever changes are made on these entities until the savechanges method is called. Entity Framework tracks the query results that return entity types.

source http://www.c-sharpcorner.com/article/no-tracking-with-entity-framework-core/