不允许在查询中显式构造实体类型

错误原因：

    from f in context.TableName
    select new MyModel()
    {
        Id = f.Id
    };

select new语句中如果指定linq自动生成的实体类并且实体类中有实体类对象，就会产生错误

用以下的代码可解决：

方法一：

注意：select new的是匿名实体，只能用匿名实体，后面代码会转换回相应实体

 

IQueryable query = from f in context.TableName
                                       join c in context.tableName_2
                                       on f.NutrientId equals c.Id
                                       where f.ContentId == ContentId
                                       select new
                                       {
                                           Id = f.Id,
                                           ContentId = f.ContentId,
                                           NutrientId = f.NutrientId,
                                           OrderValue = f.OrderValue,
                                           ContainNum = f.ContainNum,
                                           Remark = f.Remark
                                       };
                    using (context.Connection)
                   {
                        DbCommand command = context.GetCommand(query);
                        if (context.Connection.State == ConnectionState.Closed)
                        {
                            context.Connection.Open();
                        }
                        using (DbDataReader reader = command.ExecuteReader(CommandBehavior.CloseConnection))
                        {
                            result = context.Translate<MyModel>(reader).ToList();
                        }
                    }

方法二：

自定义实体类，属性CookBookAttr是实体类对象，是可行的

IList<FoodMaterialNutrient> aa = (from f in context.tablename_1
                              join c in context.tablename_2 on f.NutrientId equals c.Id
                              where f.ContentId == ContentId
                              select new MyModel()
                              {
                                  Id = f.Id,
                                  OrderValue = f.OrderValue,
                                  Remark = f.Remark,
                                  ContainNum = f.ContainNum,
                                  AttributeName = c.AttributeName,
                                  Unit = c.Unit,
                                  CookBookAttr = c
                              }).ToList();