无法将类型“匿名类型#1[]”隐式转换为“int[]”

Question

我在以下场景中尝试使用分组方法获取数据库详细信息

  //Gets MulitCourseIds from db of selected CourseIds 
        int[] _hasListCourseIds = (from mcd in _db.MultiCourseDetails
                                 where _lstCourseIds.Contains(mcd.CourseId.Value)
                                 group mcd.MultiCourseId by mcd.MultiCourseId into g
                                 select new { multiCourseId = g.Key }).ToArray();
                                   ************  error is occuring here**********

        if (_hasListCourseIds.Count > 0)
        {
            //Checks the count of courseIds from the db and selected courseIds
            foreach (var _multiCourseId in _hasListCourseIds)
            {                  
                var _courseCount = _db.MultiCourseDetails                                       
                                    .Where(x => x.MultiCourseId == _multiCourseId )
                                    .Count();
                if (_courseCount == _lstCourseIds.Count)
                {
                    return true;
                }
            }

我收到错误

无法将类型 'Anonymous Type#1[]' 隐式转换为 'int[]'

也欢迎任何改进代码的建议..

Answer 1

问题是您正在投影 anonymous 类型，但将其分配给 int 数组。由于您只投影一个属性，因此此处不需要匿名类型：-

  int[] _hasListCourseIds = (from mcd in _db.MultiCourseDetails
                             where _lstCourseIds.Contains(mcd.CourseId.Value)
                             group mcd.MultiCourseId by mcd.MultiCourseId into g
                             select g.Key).ToArray();

我假设MultiCourseId 是int。