Refreshing entities

Because of the first level cache, reloading an entity with modified database values will not refresh it.

Problem

Entity Framework Core, like other Object-Relational Mappers, uses something called a First Level Cache (also known as Identity Map) to keep track of the entities that it knows about. These are entities that were loaded from the database or ones that have been marked for persistence. This, in general, can be regarded as an optimization: when Entity Framework loads the same record over and over again, it does not need to instantiate the entity's class and hydrate it with the values coming from the database.

The problem is, what if the entity's record changes in the database and we wish to refresh the ones we have? For example, this won't work:

//retrieve an entity from the database
var myEntity = ctx.MyEntities.First();
//the entity's record changes in the database
//retrieve the entity again
//unchanged: is returned from the first level cache
myEntity = ctx.MyEntities.First();

How to solve it…

The way to solve this is to first detach it from the context, which effectively means removing it from the first level cache, like this:

//retrieve an entity from the database
var myEntity = ctx.MyEntities.First();
//the entity's record changes in the database
//detach the entity
ctx.Entry(myEntity).State = EntityState.Detached;
//retrieve the entity again
myEntity = ctx.MyEntities.First();

This way, you are sure to get the most up-to-date values.