Since this change tracker is different from the one in the context, the results are not tracked by the context. When you configure the query to use identity resolution with no tracking, we use a stand-alone change tracker in the background when generating query results so each instance is materialized only once. There's also associated entry added in the QueryTrackingBehavior enum. Just like AsNoTracking() queryable operator, we've added another operator AsNoTrackingWithIdentityResolution(). That is, you can have a no tracking query, which will do identity resolution in the results.
Starting with EF Core 5.0, you can combine both of the above behaviors in same query. So you get back a new instance of the entity even when the same entity is contained in the result multiple times. No-tracking queries don't use the change tracker and don't do identity resolution. If the result contains the same entity multiple times, you get back same instance for each occurrence. When materializing an entity, EF Core will return the same entity instance from the change tracker if it's already being tracked. Since a tracking query uses the change tracker, EF Core will do identity resolution in a tracking query. You can also change the default tracking behavior at the context instance level: = QueryTrackingBehavior.NoTracking No tracking query will also give you results based on what is in the database disregarding any local changes or added entities. You can swap an individual query to be no-tracking. If you don't need to update the entities retrieved from the database, then a no-tracking query should be used. They're quicker to execute because there's no need to set up the change tracking information. No tracking queries are useful when the results are used in a read-only scenario. Query results don't contain any entity, which is added to the context but not yet saved to the database. If the entity isn't found in the context, then EF Core will create a new entity instance and attach it to the context. EF Core won't overwrite current and original values of the entity's properties in the entry with the database values.
If EF Core finds an existing entity, then the same instance is returned. When the results are returned in a tracking query, EF Core will check if the entity is already in the context. In the following example, the change to the blogs rating will be detected and persisted to the database during SaveChanges(). Which means you can make changes to those entity instances and have those changes persisted by SaveChanges(). Tracking queriesīy default, queries that return entity types are tracking. You can view this article's sample on GitHub.
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