不允许在查询中显式构造实体类型
错误原因：
1 from f in context.TableName 2 select new MyModel() 3 { 4 Id = f.Id 5 };
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
1 IQueryable query = from f in context.TableName 2 join c in context.tableName_2 3 on f.NutrientId equals c.Id 4 where f.ContentId == ContentId 5 select new 6 { 7 Id = f.Id, 8 ContentId = f.ContentId, 9 NutrientId = f.NutrientId, 10 OrderValue = f.OrderValue, 11 ContainNum = f.ContainNum, 12 Remark = f.Remark 13 }; 14 using (context.Connection) 15 { 16 DbCommand command = context.GetCommand(query); 17 if (context.Connection.State == ConnectionState.Closed) 18 { 19 context.Connection.Open(); 20 } 21 using (DbDataReader reader = command.ExecuteReader(CommandBehavior.CloseConnection)) 22 { 23 result = context.Translate<MyModel>(reader).ToList(); 24 } 25 }
方法二：
自定义实体类，属性CookBookAttr是实体类对象，是可行的
1 IList<FoodMaterialNutrient> aa = (from f in context.tablename_1 2 join c in context.tablename_2 on f.NutrientId equals c.Id 3 where f.ContentId == ContentId 4 select new MyModel() 5 { 6 Id = f.Id, 7 OrderValue = f.OrderValue, 8 Remark = f.Remark, 9 ContainNum = f.ContainNum, 10 AttributeName = c.AttributeName, 11 Unit = c.Unit, 12 CookBookAttr = c 13 }).ToList();
