Linq-to-entities date value in database is string - asp.net

Question

Personally, I know just enough Linq to be dangerous.
The task at hand is; I need to query the DAL and return a list of objects based on a date range. Sounds simple enough, however the date is a string, and for some reason it needs to stay a string.
I spent some time with this a while ago and got a solution working but I am iterating through a list of objects and selecting individual records by date one at a time, this is badddd! If the date range spans more than a few days its slow and I don't like it, and I've even busted a few of the Sr devs around here for doing iterative queries, so I definitely don't want to be a hypocrite.
Here is the crappy iteration way... each date pegs the database, which I hate doing.
- This works
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);
}
Here is my attempt at trying to get my query to work in one db call
- This does not work... yet
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;
The error i get as follows:
I understand why I get the error, but I don't know the proper LINQ code to be able to acheive what I am trying to do. Any help will be greatly appreciated.

Answer 1

Ughh I feel dumb. I tried a bunch of tricky little things to get x.TransplantDate to just a date only string within my Linq query, E.G. 10/15/2011
where sdates.Contains(EntityFunctions.TruncateTime(Convert.ToDateTime(x.TransplantDate)).ToString())
Turns out it already is in the correct format in the database, and if i simplify it down to just
where sdates.Contains(x.TransplantDate) It works. The reason I wasnt getting any records returned was because I was testing date ranges that didnt have any data for those specific dates... UGHH.
So in conclusion this ended up working fine. And if anyone is doing something similar maybe you can learn from this example.
DateTime start = Convert.ToDateTime(RecipientSearch.TransplantSearchStartDate);
DateTime end = Convert.ToDateTime(RecipientSearch.TransplantSearchEndDate);
List<string> sdates = new List<string>();
while (start <= end)
{
string sStart = Convert.ToDateTime(start).ToString(ResourceFormatting.DateOnly);
sdates.Add(sStart);
start = start.AddDays(1);
}
selectQuery =
(ObjectQuery<DAL.Recipients>)
from x in entities.Recipients
where sdates.Contains(x.TransplantDate)
select x;