Use a Inline Table-Valued Functions with Linq and Entity Framework

Question

I created an Inline Table-Valued Functions (ITVF) in SQL Server that returns a table of values (query simplified for discussion purposes):

CREATE FUNCTION dbo.VehicleRepairStatus()
RETURNS TABLE
AS
   RETURN
       SELECT VehicleID, CurrentStatus 
       FROM VehicleRepairHistory
       ...

Which I can reference in a query:

SELECT   
    v.ID, v.Name,
    r.CurrentStatus
FROM  
    Vehicle v
LEFT OUTER JOIN 
    dbo.VehicleRepairStatus() r on v.ID = r.VehicleID

I'd like to be able to use it in Linq query:

var vehicles = await _databaseContext.Vehicles
    .Join() // join ITVF here?
    .Where(v => v.Type == 'Bus' )
    .OrderBy(v => v.Name)
    .ToAsyncList();

At some point, I may change the ITVF to include a parameter:

CREATE FUNCTION dbo.VehicleRepairStatus(@id AS INT)
RETURNS TABLE
AS
RETURN

  SELECT VehicleID, CurrentStatus 
  FROM   VehicleRepairHistory
  ...
  WHERE  VehicleID = @id

And call like a scalar:

SELECT   v.ID, v.Name
        ,(SELECT val FROM dbo.VehicleRepairStatus(v.ID)) AS CurrentStatus
FROM  Vehicle v

Linq query:

var vehicles = await _databaseContext.Vehicles
    .Select( )  // call ITVF here?
    .Where(v => v.Type == 'Bus' )
    .OrderBy(v => v.Name)
    .ToAsyncList();

Is either approach possible?

Answer 1

Yes, it's possible by utilizing the EF Core 2.1 introduced query types. Following are the required steps:

First, create a class to hold the TVF record (update it with the correct data types):

public class VehicleRepairStatus
{
    public int VehicleID { get; set; }
    public int CurrentStatus { get; set; }
}

Then register it in your OnModelCreating:

modelBuilder.Query<VehicleRepairStatus>();

Then expose it from your db context using a combination of Query and FromSql methods:

public IQueryable<VehicleRepairStatus> VehicleRepairStatus(int id) => 
    Query<VehicleRepairStatus>().FromSql($"select * from VehicleRepairStatus({id})");

And that's all.

Now you can use it inside your LINQ queries like any other IQueryable<T> returning method, for instance:

from v in db.Vehicles
from r in db.VehicleRepairStatus(v.ID)
select new { v.ID, v.Name, r.CurrentStatus }

The "select" inside FromSql method makes it composable, so the whole query is translated to SQL and executed server side.

Update: Actually this doesn't work when used as correlated subquery like the above example (see Reference to an ITVF raises a "second operation started on this context before a previous operation completed" exception). It could be used only if passing constant/variable parameters like

from r in db.VehicleRepairStatus(123)
...

See the answer to the follow up post from the link for correct implementation for correlated query scenarios.