c# - 如何将项目添加到列表

Question

我的项目中有模型。这是模型代码

public partial class Logging
{
    public string Imei { get; set; }
    public DateTime CurDateTime { get; set; }
    public Nullable<System.DateTime> GPSDateTime2 { get; set; }
    public Nullable<decimal> Latitude2 { get; set; }
    public Nullable<decimal> Longitude2 { get; set; }
    public string Speed { get; set; }
    public Nullable<int> Datatype { get; set; }
    public int Id { get; set; }
    [NotMapped]
    public TimeSpan? FirstStartDifference
    {
        get
        {
            if (CurDateTime != null)
            {
                var midnight = new DateTime(CurDateTime.Year, CurDateTime.Month, CurDateTime.Day, 00, 00, 00);
                var difference = CurDateTime - midnight;
                return difference;
            }
            return null;
        }
    }
    [NotMapped]
    public TimeSpan? LastStartDifference
    {
        get
        {
            if (CurDateTime != null)
            {
                var midnight = new DateTime(CurDateTime.Year, CurDateTime.Month, CurDateTime.Day, 23, 59, 00);
                var difference = midnight - CurDateTime;
                return difference;
            }
            return null;
        }
    }
    [NotMapped]
    public int coeff = 2;
}

我需要从数据库中获取一些项目，它是第一个条目，其中 Datatype==1最后在哪里 Datatype ==2 .

所以我把这个方法写在后端

public JsonResult GetStops()
{
    using (var ctx = new GoogleMapTutorialEntities())
    {      
        var firstitem = ctx.Loggings.Where(x => x.Datatype == 2).AsEnumerable().Select(
               x => new
               {
                   lng = x.Longitude2,
                   lat = x.Latitude2,
                   difference = (int)(x.FirstStartDifference?.TotalMinutes ?? -1) * x.coeff
               }).FirstOrDefault();
        var lastItem = ctx.Loggings.Where(x => x.Datatype == 2).AsEnumerable().Select(
               x => new
               {
                   lng = x.Longitude2,
                   lat = x.Latitude2,
                   difference = (int)(x.LastStartDifference?.TotalMinutes ?? -1) * x.coeff
               }).LastOrDefault();
        List<Logging> items = new List<Logging> {firstitem, lastItem};
        return Json(firstitem, JsonRequestBehavior.AllowGet);
    }
}

在此之后我需要添加 firstitem和 lastitem列出。

我是这样写的List<Logging> items = new List<Logging> {firstitem, lastItem};

但是我得到一个错误

Severity Code Description Project File Line Suppression State Error CS1950 The best overloaded Add method 'List.Add(Logging)' for the collection initializer has some invalid arguments Heatmap C:\Users\nemes\source\repos\Heatmap\Heatmap\Controllers\HomeController.cs 37 Active Severity Code Description Project File Line Suppression State Error CS1503 Argument 1: cannot convert from '' to 'Heatmap.Models.Logging' Heatmap C:\Users\nemes\source\repos\Heatmap\Heatmap\Controllers\HomeController.cs 37 Active

为此List<Logging> items = new List<Logging> {firstitem, lastItem};

如何将它们添加到列表中？

Answer 1

您正在返回一个匿名类型而不是 Logging。 firstitem 和 lastItem 是 Anonymous Types .将您的代码更改为:

x => new Logging
{
    Longitude2 = x.Longitude2,
    Latitude2 = x.Latitude2,
    //And other properties
}

如果您仍然遇到错误，可能是因为您无法投影到映射的实体上，那么您需要创建一个 DTO具有 Logging 实体中所需属性的类:

public class LoggingDTO
{
    public string Longitude2 { get; set; }
    public string Latitude2  { get; set; }
    //And other properties
}

然后:

x => new LoggingDTO