Add key values sugar

[ajcvickers]

It seems common to need to do things with key values--see #7308 for some examples.

Some things to consider:

• Get the key values of a tracked entry
• Lookup an entity in the state manager using key values (the state manager part of Find) Lookup tracked entities by primary key, alternate key, or foreign key #29685
• Get the FK values of a tracked entity
• Build query clauses that find given key values or compare principal and foreign key values (e.g. Explicit loading for list of entries: context.Entries(...)...Load() #7350)
• Get or set concurrency token without knowing the properties

[bricelam]

@NickStrupat likes retrieving primary key values too... 👀

[NickStrupat]

Hi @bricelam, @ajcvickers,

The first two points are supported by my project EntityFramework.PrimaryKey, but the FK values is something I didn't think of. It sounds interesting and useful.

How do you imagine the query clause building would look and/or work?

[ajcvickers]

@NickStrupat See https://github.com/aspnet/EntityFramework/blob/f9adcb64fdf668163377beb14251e67d17f60fa0/src/Microsoft.EntityFrameworkCore/Internal/EntityFinder.cs for where we do it internally. Not sure what the public API surface would look like.

[sjb-sjb]

@ajcvickers can you provide a workaround showing how to call TryGetEntry ?
I am on 1.1.1 and having a hard time wending my way through the GitHub code to implement a function dbSet.TryFind( object[] primaryKeyValues) per your bullet #2 above.

Just like in EntityFinder.FindTracked, I want to return _stateManager.TryGetEntry(key, keyValues)?.Entity as TEntity, but I don't see how to get to there from the public interface.

It could be either dbSet.TryFind or context.TryFind.

sjb

[ajcvickers]

@sjb-sjb If you're asking about public API for this, then there isn't any. The only option using the public API would be to use DbSet.Local, possibly also keeping your own map if needed for perf.

If you're willing to risk using internal APIs and are okay with reacting and updating when they break, then, try something like:

var stateManager = context.GetService<IStateManager>();
var key = context.Model.FindEntityType(typeof(TEntity)).FindPrimaryKey();
var entity = stateManager.TryGetEntry(key, new object[] { myKeyValue })?.Entity;

[sjb-sjb]

Thanks!

[ajcvickers]

Consider also creating a state manager index when a unique index (as opposed to an alternate key) is defined in the node. See #28263.