EF Core manual SQL Server sequence value

Minimal integration test showing how to obtain a SQL Server sequence value with EF Core 10 before inserting an entity. The test starts a real SQL Server 2025 container with Testcontainers, creates the sequence, reads its next value, inserts the entity, and verifies the stored row.

The working query deliberately materializes before calling Single():

var values = await db.Database
    .SqlQuery<long>($"SELECT NEXT VALUE FOR [Schema].[Custom Value]")
    .ToListAsync();
var nextValue = values.Single();

Calling SingleAsync() directly is not valid for this SQL. EF Core composes it as a derived table, but SQL Server does not allow NEXT VALUE FOR in a derived table. ToListAsync() executes the raw SQL without that composition; Single() then checks the cardinality in memory.

Prerequisites:

• .NET 10 SDK
• Docker

Run the example:

dotnet test EfNextValue.slnx