如何在MVC控制器中返回json中的列表linq？

Question

public List<Detail> GetOrderDetails()
{
    var orderDetails = (from user in db.Users
                        join detail in db.OrderDetails
                        on user.Id equals detail.UserId
                        where (detail.DateAdded != null)
                        select new Detail
                        {
                            FirstName = user.FirstName,
                            LastName = user.LastName,
                            Origin = detail.OriginCode,
                            Destination = detail.DestinationCode,
                            CarrierCode = detail.CarrierCode,
                            IsReturn = detail.IsReturn,
                            IsCancel = detail.IsCancel,
                            OrderId = detail.OrderId
                        }).FirstOrDefault();
    return Json(orderDetails);
}

此代码给出了以下错误.

无法隐式转换类型' System.Web.Mvc.JsonResult'到'System.Collections.Generic.List<TravelingAdmin.Controllers.Detail>

Answer 1

问题:

1. (your query).FirstOrDefault(); 返回一个元素而不是列表.
2. Json(x) 将x转换为包含x的json表示的字符串.

以下是您的选择:

1. 如果要返回对象列表,可以删除FirstOrDefault()并使用return (your query).ToList().
2. 您可以将方法的返回类型更改为Detail而不是List<Detail>使用return orderDetails;而不是 使用return Json(orderDetails);

更新:

从你想要"在MVC控制器中的json中返回列表"的问题的标题推断

您应该将方法更改为此

public ActionResult GetOrderDetails()
{
    var orderDetails = (from user in db.Users
                        join detail in db.OrderDetails
                        on user.Id equals detail.UserId
                        where (detail.DateAdded != null)
                        select new Detail
                        {
                            FirstName = user.FirstName,
                            LastName = user.LastName,
                            Origin = detail.OriginCode,
                            Destination = detail.DestinationCode,
                            CarrierCode = detail.CarrierCode,
                            IsReturn = detail.IsReturn,
                            IsCancel = detail.IsCancel,
                            OrderId = detail.OrderId
                        }).ToList();

    return Json(orderDetails, JsonRequestBehavior.AllowGet);
}