How to write web API make by entity framework by ADO.NET ?

Question

problem

How to write web API make by entity framework by ado.net ?

I work on SQL server 2012 with asp.net core 2 .

I need to rewrite web API below but with ado.net

so that how to make that ?

database blow :

CREATE TABLE [dbo].[User](
[Id] [int] IDENTITY(1,1) NOT NULL,
[FirstName] [nvarchar](250) NULL,
[LastName] [nvarchar](250) NULL,
[Email] [nvarchar](250) NULL,
[Phone] [nvarchar](50) NULL,
CONSTRAINT [PK_User] PRIMARY KEY CLUSTERED
(
[Id] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, _
ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
GO

/****** Object: Table [dbo].[UserMarks] Script Date: 8/15/2018 9:22:00 AM ******/
SET ANSI_NULLS ON
GO

SET QUOTED_IDENTIFIER ON
GO

CREATE TABLE [dbo].[UserMarks](
[id] [int] NOT NULL,
[userId] [int] NULL,
[mark] [decimal](18, 2) NULL,
CONSTRAINT [PK_UserMarks] PRIMARY KEY CLUSTERED
(
[id] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, _
ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]

What I have tried:

[HttpGet, Route("GetResult")]
public async Task<List<vmMarks>> GetResult()
{
List<vmMarks> query = null;

try
{
using (_ctx)
{
query = await (from um in _ctx.UserMarks
join m in _ctx.User on um.UserId equals m.Id
select new vmMarks
{
mid = (int)m.Id,
mName = m.FirstName + " " + m.LastName,
mMark = (decimal)um.Mark
}).OrderByDescending(x => x.mMark).ToListAsync();
}
}
catch (Exception ex)
{
ex.ToString();
}

return query;
}