Add when to use AsNoTracking

[Rick-Anderson]

55 minutes into 10-20-2021 EF standup

have @AndriySvyryd review what I write.

The call stack refers to snapshot change tracking. By default, EF creates a snapshot of every entity's property values when it is first tracked by a DbContext instance. The values stored in this snapshot are then compared against the current values of the entity in order to determine which property values have changed. And when querying EF uses identity resolution, so only one instance is created for a given related entity.

There are two common optimizations for this:

1. If the entities don't need to be tracked, i.e. they aren't going to be modified and then persisted with SaveChanges, then you can add .AsNoTracking() to the query, however it will no longer use identity resolution and you can get duplicate instances
2. Otherwise, the entity types can implement INotifyPropertyChanging and INotifyPropertyChanged interfaces to avoid the need for a snapshot when tracking. Or use Trackable Entities to also make it easier to work with disconnected entities.

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• ID: f988f508-f5be-9961-830d-aa569adfcce9
• Version Independent ID: 823ce300-dcb9-b51d-fe4b-5bb4625a8126
• Content: Tutorial: Read related data - ASP.NET MVC with EF Core
• Content Source: aspnetcore/data/ef-mvc/read-related-data.md
• Product: aspnet-core
• Technology: aspnetcore-data
• GitHub Login: @Rick-Anderson
• Microsoft Alias: riande