实现Entity Framework 6 Add-or-Update方法的最简单方法是什么

I have a project that uses Entity Framework 6 that does an Add-or-Update (i.e. Upsert) for a bunch of different entity types. For each of these entities, there is an surrogate integer ID (i.e. primary key), a natural key (e.g. customer ID) used for external lookups, and a set of descriptive fields (e.g. Name, Description, etc.) I have a project that uses Entity Framework 6 t