就我个人而言,我知道Linq足够危险。Linq-to-date在数据库中的日期值是字符串
- 手头的任务是;我需要查询DAL并返回基于日期范围的对象列表。听起来很简单,但日期是一个字符串,出于某种原因它需要保持一个字符串。
前段时间我花了一些时间,并得到一个解决方案的工作,但我遍历一个对象列表,并选择单个记录一次一个,这是badddd!如果日期范围超过了几天,它的速度就会变慢,我不喜欢它,甚至我还在这里为了做迭代查询而破坏了一些高级开发人员,所以我绝对不想成为一个伪君子。
下面是蹩脚的迭代方式...每个日期钉住数据库,我讨厌这样做。
- 这工作
DateTime start = Convert.ToDateTime(RecipientSearch.TransplantSearchStartDate);
DateTime end = Convert.ToDateTime(RecipientSearch.TransplantSearchEndDate);
var tempselectQuery = selectQuery;
while (start <= end)
{
tempselectQuery = selectQuery;
string sStart = Convert.ToDateTime(start).ToString(ResourceFormatting.DateOnly);
tempselectQuery = (ObjectQuery<DAL.Recipients>)tempselectQuery.Where(item => item.TransplantDate == sStart);
if (tempselectQuery.Count() != 0) TXPlistQueryDAL.AddRange(tempselectQuery.ToList());
start = start.AddDays(1);
}
这是我在试图让我的查询在一个DB调用工作
尝试 - 这不工作...但
DateTime start = Convert.ToDateTime(RecipientSearch.TransplantSearchStartDate);
DateTime end = Convert.ToDateTime(RecipientSearch.TransplantSearchEndDate);
List<string> sdates = new List<string>();
// Put my date strings in a list so I can then do a contains in my LINQ statement
// Date format is "11/29/2011"
while (start <= end)
{
string sStart = Convert.ToDateTime(start).ToString(ResourceFormatting.DateOnly);
sdates.Add(sStart);
start = start.AddDays(1);
}
// Below is where I get hung up, to do a .contains i need to pass in string, however x.TransplantDate
// includes time, so i am converting the string to a date, then using the EntityFunction to Truncate
// the time off, then i'd like to end up with a string, hence the .ToString, but, linq to entities
// thinks this is part of the sql query and bombs out... This is where I'm stumped on what to do next.
selectQuery =
(ObjectQuery<DAL.Recipients>)
from x in entities.Recipients
where sdates.Contains(EntityFunctions.TruncateTime(Convert.ToDateTime(x.TransplantDate)).ToString())
select x;
我得到的错误如下:
我明白为什么会出现错误,但我不知道适当的LINQ代码能够达到我想要做的。任何帮助将不胜感激。