无法将System.Linq.IQueryable <string>类型隐式转换为字符串

Question

我有两个名为Rank和CrewMembers的表.我想根据CrewMember的id获取Rank表中存在的rank名称.我已经将crewId作为参数传递,并且在此基础上该方法将返回该特定船员的等级.这就是我的代码 -

       public string GetRank(int CrewId)
       {

        string rank = (from r1 in context.Rank
            join r2 in context.CrewMember on r1.RankId equals r2.RankId
            where r2.CrewId == CrewId
            select r1.RankName);

        return rank;
      }

当我构建代码时,我得到以下错误 -

无法将System.Linq.IQueryable类型隐式转换为字符串

我哪里错了？

Answer 1

您应该使用FirstOrDefault或SingleOrDefault:

public string GetRank(int CrewId)
{       
    string rank = (from r1 in context.Rank
        join r2 in context.CrewMember on r1.RankId equals r2.RankId
        where r2.CrewId == CrewId
        select r1.RankName).SingleOrDefault();

    return rank;
 }