Using date comparison in LINQ when querying SharePoint OData service - linq

Question

ANSWERED: Go below to find my answer to this question.
I am trying to consume SharePoint 2010 OData from an ASP.NET MVC 3 project using LINQ. I created a default project using the ASP.NET MVC 3 project template with the Razor view engine (VS 2010). I added a service reference pointing to my SharePoint 2010 site.
In my HomeController's Index method (this is just a test project), I created a variable to hold the context and set the Credentials property of the context variable to the current default credentials.
A link query like the following works fine and I can use the created variable to access any of the data:
var query = from a in context.Alerts
select a;
This query simply gets all of the announcements from a list called Alerts in the SharePoint site. This list has fields for the Title, Content, Beginning Date, and Expiration Date.
When I change the query to the following, I do not get the expected results:
var query = from a in context.Alerts
where (a.Begins < DateTime.Now)
select a;
This query ignores the time component of the date. For example, if a.Begins contains a datetime from yesterday, the query returns the AlertItem. If on the other hand, a.Begins contains a datetime with the current date (but an earlier time) the comparison returns false (and a.Begins == DateTime.Now returns true).
If I do the following, the second LINQ query works as expected:
var query = (from a in context.Alerts
select a).ToList();
var query2 = from q in query
where (q.Begins < DateTime.Now)
select q;
What am I missing?

Answer 1

For a Linq to SharePoint query that needs to include the time element of the DateTime you can use TimeOfDay.
var next_slots = (from s in dc.HRDates
where
s.StartTime.HasValue &&
s.StartTime.Value.Date == appt.Value.Date &&
s.StartTime.Value.TimeOfDay == appt.Value.TimeOfDay
...

Answer 2

I have not used SharePoint 2010's OData. However, when querying against the SharePoint 2010 object model, the anomaly you posted is a common behavior, re: you must convert the query to a list before you can query the data.
The typical pattern here is to:
var query = someSharePointQuery.ToList();
var results = query.Where(...).First(...);
Seems odd, but this is how SP 2010 seems to work.

Answer 3

Is DateTime.Today getting used in there somewhere? I did some prototyping with LinqPad, and the only way to duplicate your results was if I had the query using "where (a.Begins < DateTime.Today)"
Here's the quick sketch I did of what it sounds like you're describing:
void Main()
{
List<Alerts> alerts = new List<Alerts>();
alerts.Add(new Alerts(DateTime.Now.AddDays(-1)));
alerts.Add(new Alerts(DateTime.Now));
var query = from a in alerts
where (a.Begins < DateTime.Now)
select a;
foreach (var element in query)
{
Console.WriteLine(element.Begins);
}
}
public class Alerts
{
public DateTime Begins {get; set;}
public Alerts(DateTime begins)
{
Begins = begins;
}
}
As I mentioned, the only way to duplicate your described results was if I changed DateTime.Now to DateTime.Today in the where clause. I would look through your code for accidental usages of the wrong DateTime method.
As an aside, I HIGHLY recommend using LinqPad for prototyping your Linq queries... It can save you time by allowing you to quickly iterate over your code and figure out what your trouble spots are. Also, it's very much worth the $50 for intellisense and other premium features.

Answer 4

After piecing together information from a lot of different sources -- none of which dealt with the exact circumstances of the problem that I am having, I've come to the following conclusion:
When querying SharePoint data using the SharePoint Object Model and Collaborative Application Markup Language (CAML), SharePoint by default does not use the time component of DateTime elements when doing comparisons. To tell SharePoint to use the time component, you must include the IncludeTimeValue = 'TRUE' property on the value type as shown here:
<Where>
<Eq>
<FieldRef Name='Begins' />
<Value Type='DateTime' IncludeTimeValue='TRUE'>
2008-03-24T12:00:00Z
</Value>
</Eq>
</Where>
I found several blog posts that referenced a bug in LINQ to SharePoint that caused the generated CAML to be output as:
<Where>
<Eq>
<FieldRef Name='dateTimeField' IncludeTimeValue='TRUE' />
<Value Type='DateTime'>
2008-03-24T12:00:00Z
</Value>
</Eq>
</Where>
Notice that the IncludeTimeValue = 'TRUE' is on the FieldRef element instead of the Value element. Since this is not the right place for that property, it causes all LINQ to SharePoint queries that perform datetime comparisons to only compare on the date component.
Since I am seeing that exact same behavior when using LINQ and WCF Data Services to connect to SharePoint, I can only assume that under the covers LINQ/WCF Data Services is producing the same invalid CAML.
The solution (assuming I still want to use LINQ/WCF Data Services) is to perform two queries (as stated in the original question). The first LINQ query pulls the list data from SharePoint and stores it in a List. The second LINQ query handles the date comparisons to only pull the data I want.
Since in my particular circumstance, I may have many entries in the SharePoint list covering a large time span but will only be interested in entries on a particular day or couple of days, I wanted to find a way not to bring back the entire list in the first query.
What I settled on was doing a <= and >= comparison to get close, and then further limiting that in my second query. So my two queries now become:
DateTime RightNow = DateTime.Now;
var query = (from a in context.Alerts
where (a.Begins <= RightNow) && (a.Expires >= RightNow)
select a).ToList();
var query2 = from q in query
where q.Begins < RightNow) && (a.Expires > RightNow)
select q;
The first LINQ statement will return all the items that I am ultimately interested in; along with a few that I'm not (because it's comparing just the date component of the datetime). The second LINQ statement will further pare that down to just those that I'm interested in.

Answer 5

I can confirm the bug with SharePoint 2010 LINQ to SharePoint not creating the correct CAML (adding IncludeTimeValue='True' to the FieldRef instead of the Value) is fixed by the October 2013 Cumulative Update to SharePoint Foundation 2010. The hotfix can be downloaded from http://technet.microsoft.com/en-us/sharepoint/ff800847.aspx.
The same bug exists also in SharePoint 2013 which I was informed by Microsoft support should be fixed in the December 2013 Cumulative Update to SharePoint Foundation 2013, but I cannot confirm this. I was informed that the fix is also deployed to Office 365, but I cannot confirm this.