LINQ to Entities 中仅支持无参数构造函数和初始化程序

Question

我得到这个错误，

 Only parameterless constructors and initializers are supported in LINQ to Entities.

当我尝试从 自定义类型投影到 DateTime 数组时，请注意 DateCreated 的类型为 DateTime。

知道怎么解决吗？

           DateTime[] data = analyticRepo.GetAll()
                                      .Where(x => DbFunctions.TruncateTime(x.DateCreated) == report.DateCreated.Date)
                                      .Select(x => new DateTime(
                                          x.DateCreated.Year,
                                          x.DateCreated.Month,
                                          x.DateCreated.Day,
                                          x.DateCreated.Hour,
                                          x.DateCreated.Minute,
                                          x.DateCreated.Second,
                                          x.DateCreated.Millisecond))
                                      .ToArray();

LINQ to Entities 仅支持无参数构造函数和初始化程序。

Answer 1

如果x.DateCreated 已经是DateTime，只需选择那个：

DateTime[] data = analyticRepo.GetAll()
                              .Where(x => DbFunctions.TruncateTime(x.DateCreated) == report.DateCreated.Date)
                              .Select(x => x.DateCreated)
                              .ToArray();

否则，您必须使用 AsEnumerable 切换到 Linq-to-Objects 上下文，然后创建新的 DateTime 对象：

DateTime[] data = analyticRepo.GetAll()
                              .Where(x => DbFunctions.TruncateTime(x.DateCreated) == report.DateCreated.Date)
                              .Select(x => x.DateCreated)
                              .AsEnumerable() // transition to Linq-to-Objects
                              .Select(x => new DateTime(
                                  x.Year,
                                  x.Month,
                                  x.Day,
                                  x.Hour,
                                  x.Minute,
                                  x.Second,
                                  x.Millisecond))
                              .ToArray();