Query Types in EF Core 2.1

Microsoft's preferred data access technology Entity Framework, or EF recently moved to version Core 2.1. This version introduced a feature called Query Types. This feature allows lightweight, read-only objects that let you map SQL queries or database views without requiring a primary key or change tracking.

To get started, define a simple class in C#:

public class OrderSummary
{
    public int OrderId { get; set; }
    public string Customer { get; set; }
    public decimal Total { get; set; }
}

In your DbContext, register it with the Query<T> method:

public class SalesContext : DbContext
{
    public DbQuery<OrderSummary> OrderSummaries { get; set; }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Query<OrderSummary>()
            .ToView("vwOrderSummary");
    }
}

Then you can query it just like any other entity:

var summaries = context.OrderSummaries
                       .Where(o => o.Total > 1000)
                       .ToList();

Because Query Types are read-only, EF Core never tries to insert or update them. They are ideal for reports, joins, and projections where you don't need full change tracking.