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Casting Nhibernate result into IDictionary<string,int>

I am trying to convert the result of the query into IDictionary
Here string will contain orderId and the int will contain the TradedQuantity
The query below should join three objects Order, OrderRevision and OrderEvent.
1 Order can have many orderRevisions
1 OrderRevision can have many orderEvents
What the query is trying to do is to inner join three objects and get all order objects whose order id matches the list of orderids supplied to it. Then it does a group by based on orderId and gets the latest TradedQuantity from orderEvents object. LatestTradedQuantity will be the TradedQuantityFrom latest OrderEvent. For now the latest orderevent can be regarded as the one that has highest OrderEventId value.
OrderRevision revisionAlias = null;
Order orderAlias = null;
var query =
Session.QueryOver<OrderEvent>()
.JoinAlias(oe => oe.OrderRevision,() => revisionAlias)
.JoinAlias(oe => oe.OrderRevision.Order,() => orderAlias)
.Where(x => x.OrderRevision.Order.SourceSystem.Name.ToLower() == sourceSystem.ToLower())
.WhereRestrictionOn(x => x.OrderRevision.Order.Id).IsIn(orderIds.ToList())
.SelectList(list => list.SelectGroup(x => x.OrderRevision.Order.SourceOrderIdentifier)
.SelectMax(x => x.Id).Select(x => x.TradedQuantity))
.Select(x => new KeyValuePair<string, int?>(x.OrderRevision.Order.SourceOrderIdentifier, x.TradedQuantity)
);
As this query does not do what is supposed to. Could you please help and let me know how the result can be cast into IDictionary?

You have tagged your question with linq-to-nhibernate, so I guess using it instead of queryover would suit you. With Linq, use a sub-query for selecting the "max" order events ids for each order, then query them and project them to a dictionary.
using System.Linq;
using NHibernate.Linq;
...
var orderEventsIdsQuery = Session.Query<OrderEvent>()
.Where(oe => orderIds.Contains(oe.OrderRevision.Order.Id))
.GroupBy(oe => oe.OrderRevision.Order.SourceOrderIdentifier,
(soi, oes) => oes.Max(oe => oe.Id));
var result = Session.Query<OrderEvent>()
.Where(oe => orderEventsIdsQuery.Contains(oe.Id))
.ToDictionary(oe => oe.OrderRevision.Order.SourceOrderIdentifier,
oe => oe.TradedQuantity);
This should do the job. I do not use QueryOver and I will not try to give an answer for doing it with QueryOver.

Group By struct list on multiple columns in C#

I am having a struct as
public struct structMailJob
{
public string ID;
public string MailID;
public int ResendCount;
public int PageCount;
}
and a list as
List<structMailJob> myStructList = new List<structMailJob>();
I have loaded data in myStructList from database and want myStructList data in a new list after grouping by MailID and ResendCount.
I am trying as:
List<structMailJob> newStructList = new List<structMailJob>();
newStructList = myStructList.GroupBy(u => u.MailID, u=>u.ResendCount)
.Select(grp => new { myStructList = grp.ToList() })
.ToList();
but unable to do that as getting error message - cant implicitly convert generic list to structMailJob.

I think that you are looking for is the following:
var newStructList = myStructList.GroupBy(smj => new { smj.MailID, smj.ResendCount })
.Select(grp => new
{
MailID = grp.Key.MailID,
ResendCount = grp.Key.ResendCount
MailJobs = grp.Select(x=>new
{
x.ID,
x.PageCount
}).ToList()
})
.ToList();
Note that we changed the GroupBy clause to the following one:
GroupBy(smj => new { smj.MailID, smj.ResendCount })
Doing so, the key on which the groups would be created would be consisted of both MailID and ResendCount. By the way the former GroupBy clause isn't correct.
Then having done the grouping, we project each group to an object with three properties, MailID and ResendCout, which are the components of the key and list of anonymous type object with two properties, ID and PageCount, which we gave it the name MailJobs.
Last but not least you will notice that I didn't mention the following
List<structMailJob> newStructList = new List<structMailJob>();
I just used the var and declared the newStructList. I don't think that you stated in your post makes sense. How do we expect to get a list of the same objects after grouping them? So I assumed that you might want is the above.
However, I thought you might want also something like this and you didn't want to refer to Grouping.
myStructList = myStructList.OrderBy(smj => smj.MailID)
.ThenBy(smj => smj.ResendCount)
.ToList();

Linq Query is completely incorrect, following are the important points:
myStructList.GroupBy(u => u.MailID, u=>u.ResendCount) // Incorrect grouping
myStructList.GroupBy(u => new {u.MailID, u.ResendCount }) // Correct grouping, which will do by two columns MailID and ResendCount, last one was only doing by MailID and was using ResendCount for result projection
Now the result is of type IEnumerable<IGrouping<AnonymousType,structMailJob>>, so when you do something like Select, it will end up creating Concatenated List of type IEnumerable<List<structMailJob>> (Removed the assignment to myStructList inside the Select, as that was not correct):
.Select(grp => grp.ToList())
Correct code would require you to flatten using SelectMany as follows:
newStructList = myStructList.GroupBy(u => new {u.MailID, u.ResendCount})
.SelectMany(grp => grp.ToList()).ToList();
Assign it to newStructList, but this code has little use, since literally newStructList is exactly same as myStructList post flattening, ideally you shall be able to use the grouping, so that you can get a subset and thus the correct result, however that depends on your business logic

I don't know if I got your question right but it seems to me you missed the 'Group by' signature.
List<structMailJob> myStructList = new List<structMailJob>();
List<structMailJob> newStructList = new List<structMailJob>();
newStructList = myStructList
// .GroupBy(/*Key Selector */u => u.MailID, /*Element Selector*/u=>u.ResendCount)
.GroupBy(u => new { u.MailID, u.ResendCount }) // broup by MailID, ResendCount
// Note no Element Selector , the 'STRUCT' is 'SELECTED'
.Select(grp => {
// NOte: Key == Anonymous {MailID, ResendCount }
return grp;
})
// otherwise you get a IEnumerable<IEnumerable<T>> instead of IEnumerable<T> because you grouped it
.SelectMany(x=>x)
.ToList();

If Mrinal Kamboj's answer is what you are looking for, then you could use the following as an alternative:
var orderedList = myStructList.OrderBy(x => x.MailID).ThenBy(x => x.ResendCount);

Create Multiple Objects Single LINQ EF Method

List<MyObject> objects = await item.tables.ToAsyncEnumerable()
.Where(p => p.field1 == value)
.Select(p => new MyObject(p.field1,p.field2))
.ToList();
^ I have something like that, but what i'm wondering, is there anyway way to add a second object creation, in the same select? eg. new MyObject(p.field3,p.field4) ? and add it to the same list? order does not matter.
I know could do this with multiple calls to database or splitting up lists into sections, but is there way to do this in single line?

You could create it as a tuple.
List<Tuple<MyObject1, MyObject2>> = query.Select(x => Tuple.Create(
new MyObject1
{
// fields
},
new MyObject2
{
//fields
}))
.ToList();
From my testing in Linqpad, it seems that this will only hit the database once.
Alternatively, you could just select all the fields you know you'll need from the database to create both:
var myList = query.Select(x => new { FieldA = x.FieldA, FieldB = x.FieldB }).ToList(); //hits db once
var object1s = myList.Select(x => new MyObject1(x.FieldA));
var object2s = myList.Select(x => new MyObject1(x.FieldB));
var bothLists = object1s.Concat(object2s).ToList();

What you'd want to do is use the SelectMany method in linq. Which will select all the items from an array. The array can be created anonymously as seen below.
List<MyObject> objects = await item.tables.ToAsyncEnumerable()
.Where(p => p.field1 == value)
.SelectMany(p => new []{new MyObject(p.field1,p.field2), new MyObject(p.field3,p.field4)})
.ToList();
Hope that solves you problem!

If you use query syntax instead of method chaining, you can use the let operator to accomplish this. Note that the SQL generated may not be exactly performant as this article shows, but it should work for you if you're after a subquery.

You could try creating an array of objects and then flattening with SelectMany:
List<MyObject> objects = await item.tables.ToAsyncEnumerable()
.Where(p => p.field1 == value)
.Select(p => new [] {
new MyObject(p.field1,p.field2),
new MyObject(p.field3,p.field4)
})
.SelectMany(g => g)
.ToList();
But I suspect you'll have problems getting EF to translate that to a query.

Remove duplicates of a List, selecting by a property value in C#?

I have a list of objects that I need some duplicates removed from. We consider them duplicates if they have the same Id and prefer the one whose booleanValue is false. Here's what I have so far:
objects.GroupBy(x => x.Id).Select(x => x.Where(y => !y.booleanValue));
I've determined that GroupBy is doing no such grouping, so I don't see if any of the other functions are working. Any ideas on this? Thanks in advance.

You can do this:
var results =
from x in objects
group x by x.Id into g
select g.OrderBy(y => y.booleanValue).First();
For every Id it finds in objects, it will select the first element where booleanValue == false, or the the first one (if none of them have booleanValue == false).
If you prefer fluent syntax:
var results = objects.GroupBy(x => x.Id)
.Select(g => g.OrderBy(y => y.booleanValue).First());

Something like this should work:
var result =
objects.GroupBy(x => x.Id).Select(g =>
g.FirstOrDefault(y => !y.booleanValue) ?? g.First())
This assumes that your objects are of a reference type.
Another possibility might be to use Distinct() with a custom IEqualityComparer<>.

This partially answers the question above, but I justed need a really basic solution:
objects.GroupBy(x => x.Id)
.Select(x => x.First())
.ToArray();
The key to getting the original object from the GroupBy() is the Select() getting the First() and the ToArray() gets you an array of your objects, not a Linq object.

OrderBy with Dynamic Linq and one to many relationship in EF

I'd like to implement a module for filtering and paging. I understand that to suceed I had to use Dynamic Linq or Reflection, so I started trying to make it work .. but since the field that contains the text to be filtered in a one to many relationship EF not like it.
This code work fine .. but is static :
List<Domain.Entities.Action> actions = db.Actions.Include("Menus").Include("ActionDetails")
.Where(x => x.ActionDetails.Any(y => y.Language.Culture == _currentCulture))
.OrderBy(y => y.ActionDetails.Select(z => z.Title).Max()).Skip((pager.Index - 1) * pager.Take).Take(pager.Take)
.ToList();
I want the
.Select(z => z.Title)
Dynamic..
Can someone help me .. I Try a lot of thing .. but no sucess
Ju.

In order to accomplish this you need to pass in a parameter of Funt<Action, TResultType> searchCriteria
Not sure what your method signature is like but this would work if you plan on returning a List<string>
public List<string> PerformSearch(Func<Action, string> selectCriteria)
{
return db.Actions.Include("Menus").Include("ActionDetails")
.Where(x => x.ActionDetails.Any(y => y.Language.Culture == _currentCulture))
.OrderBy(y => y.ActionDetails.Select(**selectCriteria**).Max())
.Skip((pager.Index - 1) * pager.Take).Take(pager.Take)
.ToList();
}