Entity Framework - retrieve ID before 'SaveChanges' inside a transaction

Question

In Entity Framework - Is there any way to retrieve a newly created ID (identity) inside a transaction before calling \'SaveChanges\'?

I need the ID for a second inse

Answer 1

As others have already pointed out, you have no access to the increment value generated by the database before saveChanges() was called – however, if you are only interested in the id as a means to make a connection to another entity (e.g. in the same transaction) then you can also rely on temporary ids assigned by EF Core:

Depending on the database provider being used, values may be generated client side by EF or in the database. If the value is generated by the database, then EF may assign a temporary value when you add the entity to the context. This temporary value will then be replaced by the database generated value during SaveChanges().

Here is an example to demonstrate how this works. Say MyEntity is referenced by MyOtherEntity via property MyEntityId which needs to be assigned before saveChanges is called.

var x = new MyEntity();        // x.Id = 0
dbContext.Add(x);              // x.Id = -2147482624 <-- EF Core generated id
var y = new MyOtherEntity();   // y.Id = 0
dbContext.Add(y);              // y.Id = -2147482623 <-- EF Core generated id
y.MyEntityId = x.Id;           // y.MyEntityId = -2147482624
dbContext.SaveChangesAsync();
Debug.WriteLine(x.Id);         // 1261 <- EF Core replaced temp id with "real" id
Debug.WriteLine(y.MyEntityId); // 1261 <- reference also adjusted by EF Core

The above also works when assigning references via navigational properties, i.e. y.MyEntity = x instead of y.MyEntityId = x.Id