不能使用集合初始化器实现XYZ类型，因为它没有实现'System.Collections.IEnumerable‘

Question

我有以下课程：

public class CommentList 
{
    string ItemType;
    string Comment1;
    string Status1;
    string DiscussionBoardId;
    Guid CourseId;
    Guid CommentID;
}

我试图执行以下LINQ语句：

List<CommentList> query=
    from c in db.Comments
    join s in db.Status on c.StatusId equals s.StatusId
    join d in db.DiscussionBoards 
        on c.DiscussionBoardId equals d.DiscussionBoardId
    where d.CourseId=="CourseID"
    orderby d.ItemType, d.DiscussionBoardId
    select new CommentList {
        d.ItemType,
        c.Comment1,
        s.Status1,
        c.DiscussionBoardId,
        d.CourseId,
        c.CommentID
    };

问题是，编辑器正在抱怨select语句的第一个括号。据说：

无法使用集合初始化器实现“CommentList”类型，因为它没有实现“System.Collection. initializer”。

有人能帮帮我告诉我我做错了什么吗？

Answer 1

使您的字段public，因为它们现在是不可访问的。

public class CommentList
{
  public string ItemType;
  public string Comment1;
  public string Status1;
  public string DiscussionBoardId;
  public Guid CourseId;
  public Guid CommentID;
}

在你的初始化器中设置它们。

select new CommentList
{
    ItemType = d.ItemType,
    Comment1 = c.Comment1,
    Status1 = s.Status1,
    DiscussionBoardId = c.DiscussionBoardId,
    CourseId = d.CourseId,
    CommentID = c.CommentID
};

Answer 2

只是对我的评论做了更全面的跟进。您要做的是使用对象初始化，它要求您为属性命名。它认为你正在尝试的是集合初始化

List<CommentList> query = from c in db.Comments
                join s in db.Status on c.StatusId equals s.StatusId
                join d in db.DiscussionBoards on c.DiscussionBoardId equals d.DiscussionBoardId
                where d.CourseId == "CourseID"
                orderby d.ItemType, d.DiscussionBoardId
                select new CommentList
                {
                    ItemType = d.ItemType,
                    Comment1 = c.Comment1,
                    Status1= s.Status1,
                    DiscussionBoardId = c.DiscussionBoardId,
                    CourseId = d.CourseId,
                    CommentId = c.CommentID
                };

Answer 3

初始化不正确。您需要为显式属性赋值。

select new CommentList
{
    ItemType = d.ItemType,
    Comment1 = c.Comment1,
    Status1 = s.Status1,
    DiscussionBoardId = c.DiscussionBoardId,
    CourseId = d.CourseId,
    CommentID = c.CommentID
};