c# - 使用“where”：无法将 lambda 表达式转换为“bool”类型

Question

我有如下所示的实体框架代码。在 where 条件下出现以下错误。

无法将 lambda 表达式转换为类型“bool”，因为它不是委托类型

如何克服这个错误？这个错误的原因是什么？

    static void Main(string[] args)
    {

        ClubCreation();
        List<Club> selectedClubs = GetClubs("club1");

    }

    public static void ClubCreation()
    {

        string connectionstring = "Data Source=.;Initial Catalog=NerdDinners;Integrated Security=True;Connect Timeout=30";
        using (var db = new NerdDinners(connectionstring))
        {

            Club club1 = new Club();
            club1.ClubName = "club1";

            Club club2 = new Club();
            club2.ClubName = "club2";

            Club club3 = new Club();
            club3.ClubName = "club3";

            db.Clubs.Add(club1);
            db.Clubs.Add(club2);
            db.Clubs.Add(club3);

            int recordsAffected = db.SaveChanges();


        }
    }

    public static List<Club> GetClubs(string clubName)
    {
        string connectionstring = "Data Source=.;Initial Catalog=NerdDinners;Integrated Security=True;Connect Timeout=30";
        using (var db = new NerdDinners(connectionstring))
        {

            Club club1 = new Club();
            Club club2 = new Club();
            Club club3 = new Club();


            var query = from o in db.Clubs
                        where (p => p.ClubName == "club1")
                        select o;

            return query.ToList();





        }
    }

Answer 1

而不是where (p => p.ClubName == "club1")使用：

var query = from o in db.Clubs
            where  o.ClubName == "club1"
            select o;

可能你对方法链感到困惑：

var query = db.Clubs.Where(p => p.ClubName == "club1");

Answer 2

该=>语法用于方法链表示法。您可能还想使用clubName变量而不是"club1".

var query = db.Clubs.Where (p => p.ClubName == clubName);

这与此相同（这是您查询的正确语法）：

var query = from o in db.Clubs
            where o.ClubName == clubName
            select o;

Answer 3

        var query = from o in db.Clubs
                    where o.ClubName == "club1"
                    select o;

Answer 4

在我尝试的时候在 asp mvc Razor 中：

@if (modelItem => item.Id == 1)
 {

<span class="badge progressbar-success">Approved</span> 

 }

无法将 lambda 表达式转换为类型“bool”，因为它不是委托类型

解决方案：

@if (Model.FirstOrDefault().Id == 1)
{

<span class="badge progress-bar-success">Approved</span>

}

希望能帮助某人。

Answer 5

var query = from o in db.Clubs
            where o.ClubName == "club1"
            select o;