C＃实体框架-如何返回具有最大值的列表？

Question

To start, I have a database modeled using the Entity Framework with the following structure:

Pedidos :
--------
IDPedidoDetalhe (int, not null)
IDPedido  (int, not null)
Aditamento (int, not null)
Semana  (int, null)
Ano  (int, null)
Titulo  (nvarchar(250), null)

I'm trying to create a query that finds the line of the table with the "IDPedido" required and the max value for "Aditamento". To find the max value for a required item (npedido), i use:

List<Pedidos> lista = db.Pedidos.Where(m => m.IDPedido == npedido).ToList();
var pedido = lista.Select(m => m.Aditamento).Max(x => x);

But I want the line in the list (all the columns) and no just the value for "Aditamento".

Can you help me, with this query?

Answer 1

You are loosing all fields of Pedido entity when you are doing projection to Aditamento with Select(m => m.Aditamento) . For getting single Pedido by id, with max Aditamento value you should simply order filtered Pedidos by Aditamento and select first one:

var pedido = db.Pedidos.Where(p => p.IDPedido == npedido)
               .OrderByDescending(p => p.Aditamento)
               .FirstOrDefault();

For getting all Pedidos with max Aditamento value you need to group filtered Pedidos by Aditamento and select group with max key value:

var pedidos = db.Pedidos.Where(p => p.IDPedido == npedido)
                .GroupBy(p => p.Aditamento)
                .OrderByDescending(g => g.Key)
                .FirstOrDefault();

If you want list, then check if you have found any pedidos by id and convert group to list:

if (pedidos != null)
{
    List<Pedido> result = pedidos.ToList();
}

Answer 2

This should do:

List<Pedidos> lista = db.Pedidos.Where(m => m.IDPedido == npedido).ToList();

var maxValue= lista.Max(x => x.Aditamento);

// IEnumerable with all lines that have the "maxValue"
var lineWithMaxValue = lista.Where(x => x.Aditamento == maxValue);