Develop Reference

NOT IN Condition in Linq

I have a simple scenario.I want to list out all the employees except the logged in user.
Similar SQL Condition is
select * from employee where id not in(_loggedUserId)
How can I acheive the above using LINQ.I have tried the following query but not getting the desired list
int _loggedUserId = Convert.ToInt32(Session["LoggedUserId"]);
List<int> _empIds = _cmn.GetEmployeeCenterWise(_loggedUserId)
.Select(e => e.Id)
.Except(_loggedUserId)
.ToList();

Except expects argument of type IEnumerable<T>, not T, so it should be something like
_empIds = _cmn.GetEmployeeCenterWise(_loggedUserId)
.Select(e => e.Id)
.Except(new[] {_loggedUserId})
.ToList();
Also note, this is really redundant in the case when exclusion list contains only one item and can be replaces with something like .Where(x => x != _loggedUserId)

Why not use a very simple Where condition?
_empIds = _cmn.GetEmployeeCenterWise(_loggedUserId).Where(e=>e.Id != _loggedUserId).ToList();

The title of your question is how to perform a not in query against a database using LINQ. However, as others have pointed out your specific problem is better solved by a using users.Where(user => user.Id != loggedInUserId).
But there is still an answer on how to perform a query against a database using LINQ that results in NOT IN SQL being generated:
var userIdsToFilter = new[] { ... };
var filteredUsers = users.Where(user => !userIdsToFilter.Contains(user.Id));
That should generate the desired SQL using either Entity Framework or LINQ to SQL.
Entity Framework also allows you to use Except but then you will have to project the sequence to ID's before filtering them and if you need to original rows you need to fetch them again from the filtered sequence of ID's. So my advice is use Where with a Contains in the predicate.

Use LINQ without filtering. This will make your query execute much faster:
List<int> _empIds = _cmn.GetEmployeeCenterWise(_loggedUserId)
.Select(e => e.Id).ToList();
Now use List.Remove() to remove the logged-in user.
_empIds.Remove(_loggedUserId);

Sitecore: efficient way to use LINQ to compare against an ID

I have a LINQ query retrieving a list of , such as this:
var results = SearchContext.GetQueryable<Person>()
.Where(i => i.Enabled)
.Where(i => i.TemplateName == "Person")
.Random(6);
Each object of type "Person" has a "Location" field which is also a Glass mapped item, and hence has an ID; I would like to only select items whose Location has a specific ID.
How can I go about doing this in an efficient manner?
EDIT: I should probably clarify that I am unable to perform this comparison, efficiently or not. Because the GUID is an object and I cannot perform ToString in a LINQ query, I am unable to only pick the items whose Location item has a specific ID. Any clues on how this could be achieved?
EDIT 2: Adding the clause
.Where(i => i.Location.Id == this.Id)
Doesn't work, for... some reason, as I'm unable to debug what LINQ "sees". If I convert the other ID I'm comparing it against to string this way:
var theOtherID = this.Id.ToString("N");
Then it works with this LINQ line:
.Where(i => i["Location"].Contains(theOtherID))
I still have no idea why.

One approach is to include a separate property on Person that is ignored by Glass mapper, but can be used in searches:
[SitecoreIgnore]
[Sitecore.ContentSearch.IndexField("location")]
public Sitecore.Data.ID LocationID { get; set; }
You can use this in your search as follows:
Sitecore.Data.ID locationId = Sitecore.Data.ID.Parse(stringOrGuid);
var results = SearchContext.GetQueryable<Person>()
.Where(i => i.Enabled)
.Where(i => i.TemplateName == "Person")
.Where(i => i.LocationID == locationId)
.Random(6);
I think the efficiency of using multiple where clauses vs. conditionals is debatable. They will likely result in the same Lucene query being performed. I would prefer readability over optimization in this instance, but that's just me.

I can't think of a more efficient methods than using a simple where statement like in:
var results = SearchContext.GetQueryable<Person>()
.Where(i => i.Enabled && i.TemplateName == "Person" &&
i.Location != null && i.Location.Id == 1)
.Random(6);
Keep in mind that if you use the && statement instead of a where for each parameter, you reduce the complexity of the algorithm.
You could also use an Inverse Navigation Property on Location to a virtual ICollection<Person> and then be able to do this:
var results = SearchContext.GetQueryable<Location>()
.Where(i => i.Id == 1 && i.Persons.Where(p => p.Enabled && p.TemplateName == "Person").Any())
.Random(6);
The first option would still be the most efficient, because the second one uses sub-queries. But it is worth knowing you can do your search the other way.

EF: LINQ - orderby using child collection with condition - ArgumentException

I'm running into troubles trying to sort IQueryable of my EF Entity.
My object structure is something like this:
Item
Item.CustomFieldValue [List<CustomFieldValue>]
Item.CustomFieldValue.DefinitionID
Item.CustomFieldValue.Value
and I'm working with
IQueryable<Item>
I'd need to sort it conditionally with values having desired definition id being sorted first something like this:
queryable = queryable
.OrderBy(p => p.CustomFieldValue
.Where(p2 => p2.DefinitionID == defId)
.Select(p3 => p3.Value)
.OrderBy(p4 => p4)
);
This however throws ArgumentException "DbSortClause expressions must have a type that is order comparable.".
I indeed understand what's the exception trying to say to me, I just can't figure out on how to change this so that valid query is generated.
Any help greatly appreciated
EDIT:
To bring some more light into the issue, I want to achieve something similar that this query does
SELECT * FROM ticketnumber t, customfieldvalue c
WHERE t.id like '%00000047%' and c.ticketnumberid = t.id
ORDER BY CASE
WHEN DefinitionId = 2125 THEN 1
ELSE 2
END, c.Value ASC
Alternatively, as time is starting to become a factor for me, is there a way I could append OrderBy in string form?

You probably want to use FirstOrDefault() at the end of the end of the first OrderBy so you won't be dealing with enumerables but with values.
queryable = queryable
.OrderBy(p => p.CustomFieldValue
.Where(p2 => p2.DefinitionID == defId)
.Select(p3 => p3.Value)
.OrderBy(p4 => p4)
.FirstOrDefault()
);

Modification of Joanvo's answer did the trick, this is the working code [I've removed the inner OrderBy]
queryable = queryable.OrderBy(p => p.CustomFieldValue.Where(p2 => p2.DefinitionID == defId).Select(p3 => p3.Value).FirstOrDefault());

need help around IQueryable query result

Assuming following tables
Person
id
name
PersonTeam
id
person_id
is_supervisor
team_id
Team
id
TimeSheet
id
team_id
I would like to obtain all TimeSheets for a supervisor. I got name of supervisor, then I need select which team he is got supervisor role. Then select all time sheet of those teams.
I believe following query does
var allTimeSheets = ctx.PersonTeam.Where(y => y.Person.name == supervisor_name).Where(x => x.is_supervisor == true).Select(z => z.Team).Select(t => t.TimeSheet);
afer this operation I cannot understand allTimeSheets is a
IQueryable<ICollection<TimeSheet>>
I expected more a
<ICollection<TimeSheet>>
or any IEnumrable.
Then questions are :
why I got that kind of result ?
how to obtain TimeSheet[] where I got IQueryable < ICollection < TimeSheet > > ?

why did I get that kind of result ? I expected more a ICollection<TimeSheet>
An IQueryable<T> is an IEnumerable<T>. The reason it's returning an IQueryable is so you can chain other methods like OrderBy onto it and project those to the actual SQL.
I just realized what you're asking. To "flatten" the collection of collections, use SelectMany instead of two chained Selects:
var allTimeSheets = ctx.PersonTeam
.Where(y => y.Person.name == supervisor_name
&& y.is_supervisor == true)
.SelectMany(z => z.Team, (z, t) => t.TimeSheet);
The answer to your second question still applies:
how do I obtain a TimeSheet[] from a IQueryable<ICollection<TimeSheet>>
(first of all use the first part to change to an IQueryable<TimeSheet>)
You can call one of the "conversion" methods like ToArray, ToList, to "hydrate" the query into a concrete type.
You can also call "AsEnumerableto cast to anIEnumerableto convert the query to Linq-To-Objects, which has better support for custom functions in sorts, filters, etc. Note that callingAsEnunerable` does no immediately fetch the objects, but will do as as soon as the collection in enumerated.

Use a function within LINQ

I am using LINQ to create a list. But I want to use a function at the end to generate the object iself, something LINQ complains about
LINQ to Entities does not recognize the method 'WashroomStatusItem GetWashroomStatusForItem(WashroomStatus)' method, and this method cannot be translated into a store expression.
What am I doing wrong?
var query = (from c in context.WashroomStatus
where c.WashroomId == GroupItem.WashroomID
select GetWashroomStatusForItem(c));
private WashroomStatusItem GetWashroomStatusForItem(WashroomStatus item)
{
WashroomStatusItem temp = new WashroomMonitorWCF.WashroomStatusItem();
//do stuff with it
return temp;
}

The problem is that the SQL conversion can't convert your method into SQL. You should use AsEnumerable() to "switch" from the out-of-process provider to LINQ to Objects. For example:
var query = context.WashroomStatus
.Where(c => c.WashroomId == GroupItem.WashroomID)
.AsEnumerable()
.Select(c => GetWashroomStatusForItem(c));
Note that if GetWashroomStatusForItem only uses some properties, you may want to project to those separately first, to reduce the amount of information fetched from the server:
var query = context.WashroomStatus
.Where(c => c.WashroomId == GroupItem.WashroomID)
.Select(c => new { c.Location, c.Date };
.AsEnumerable()
.Select(p => GetWashroomStatusForItem(p.Location, p.Date));

Jon Skeet's answer is correct, but I'd add that depending on the nature of GetWashroomStatusForItem(), it should probably either be broken down into LINQ statements and added into the query itself, or it should be executed after the query has returned.
So, lets say GetWashroomStatusForItem() looks something like this: note that this is extremely oversimplified.
public static WashroomStatus GetWashroomStatusForItem(Item c)
{
return c.WashroomStatus;
}
it should just be added to the LINQ query like this:
var query = (from c in context.WashroomStatus
where c.WashroomId == GroupItem.WashroomID
select c.WashroomStatus);
But if it relies heavily on stuff not in the db, I'd just end the Linq statement before you get the WashroomStatus, and then call GetWashroomStatusForItem() on the results. It's not gonna a performance difference since Linq uses lazy evaluation, and you generally want to keep db operations separate from "programmatic" ones.