c# - 带有动态字段名称的 OrderBy 上的 .NET Core 3 InvalidOperationException

Question

我正在从 .NET Core 2 o 3 版本迁移现有的 Web API。
经过几个问题，我设法使它工作，除了按列名的 Dynamic OrderBy。

这是我的代码，它与 .net core 2 配合得很好:

public async Task<IEnumerable<Clientes_view>> GetClientes(int bActivos, int nRegistroInic, int nRegistros, string sOrdenar, 
        int nSentido, string sFiltro, int nTipo = -1, int idCliente = -1)
    {
        var clientes = this.context.Set<Clientes_view>()
           .Where(e => e.RazonFantasia.Contains(sFiltro) || e.RazonFantasia.Contains(sFiltro)
               || e.Cuit.Contains(sFiltro) || e.Mail.StartsWith(sFiltro) || string.IsNullOrEmpty(sFiltro))
           .Where(e => (e.Activo && bActivos == 1) || bActivos == -1 || (!e.Activo && bActivos == 0))
           .Where(e => e.IdTipoCliente == nTipo || nTipo == -1)
           .Where(e => e.IdCliente == idCliente || idCliente == -1);

        if (!string.IsNullOrEmpty(sOrdenar))
        {
            var propertyInfo = this.context.Set<Clientes_view>().First().GetType().GetProperty(sOrdenar, 
                BindingFlags.IgnoreCase | BindingFlags.Public | BindingFlags.Instance);

            if (propertyInfo != null) if (nSentido == -1) clientes = clientes.OrderByDescending(e => propertyInfo.GetValue(e, null));
                else clientes = clientes.OrderBy(e => propertyInfo.GetValue(e, null));
        }

        clientes = clientes.Skip(nRegistroInic).Take(nRegistros);

        return await clientes.ToListAsync();
    }

我得到的错误如下:

System.InvalidOperationException: The LINQ expression 'DbSet .Where(c => True) .Where(c => c.Activo && True || False || False) .Where(c => True) .Where(c => True) .OrderBy(c => __propertyInfo_3.GetValue( obj: c, index: null))' could not be translated. Either rewrite the query in a form that can be translated, or switch to client evaluation explicitly by inserting a call to either AsEnumerable(), AsAsyncEnumerable(), ToList(), or ToListAsync().

有什么想法吗？
谢谢!

Answer 1

您需要实际生成成员访问表达式，您所做的只是使用反射来获取某个对象的值，并将其作为表达式提供。那是行不通的，查询提供者将无法翻译它。

你需要做这样的事情:

if (!String.IsNullOrEmpty(sOrdenar))
{
    var type = typeof(Clientes_view);
    var prop = type.GetProperty(sOrdenar);
    if (prop != null)
    {
        var param = Expression.Parameter(type);
        var expr = Expression.Lambda<Func<Clientes_view, object>>(
            Expression.Convert(Expression.Property(param, prop), typeof(object)),
            param
        );
        if (nSentido == -1)
            clientes = clientes.OrderByDescending(expr);
        else
            clientes = clientes.OrderBy(expr);
    }
}