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How do I drill down to specific data in my LINQ query result?

I want to drill down into a particular item in my data and output the list of results to the output window. My query result looks like this
private IEnumerable<DataRow> _data;
var query = from data in this._data
group data by data.Field<string>("Form Name") into groups //same as Form ID
select new
{
formName = groups.Key,
items = from d in groups
group d by d.Field<string>("Item Name") into grps
let name = grps.Key
let documentIDGroups = grps.GroupBy(t => t.Field<string>("Document ID"))
let documentIDGroupsCount = documentIDGroups.Count()
let distinctDocumentValueCount = from data in documentIDGroups
select new
{
docID = data.Key,
distinctDocValueCount = data.Where(t => string.IsNullOrEmpty(t.Field<string>("Document Value").Trim()) == false).Select(t => t.Field<string>("Document Value")).Distinct().Count()
}
let sum = distinctDocumentValueCount.Sum(t => t.distinctDocValueCount)
let distinctItemsNames = from data in grps
select data.Field<string>("Item Name").Distinct().Count()
let count = distinctItemsNames.Count()
select new
{
itemName = name,
documentIDGroups,
documentIDGroupsCount,
averageChoices = Math.Round(((decimal)sum / documentIDGroupsCount), 2),
distinctDocumentValueCount,
sum
}
};
So on that query result I want to drill down into a particular form name, and from there get a particular Item Name and so on
so the first step is to get the grouping of items and I have
var items = from d in query where d.formName == "someName" select d.items;
but I don't know how to isolate the items by a particular string.
I want to do the following
var item = from d in items where d.itemName == "anItemName" select d;
But I don't know the syntax.

Use the .FirstOrDefault extension if you expect a single item to be returned from your query. SO:
var item = (from d in items where d.itemName == "anItemName" select d).FirstOrDefault();

LINQ get find all with id in list

I am trying to figure out non query way to do return a list of all objects if their ID is in test list. Example below:
Hero - table
Columns: id = INT , name = STRING, age = INT, power = INT;
var testList = {1,2,3};
var secondArray = {};
foreach (var id in testList )
{
// check if ID in database
var item = db.Hero.ToList().Find(o => o.Id = id);
if( item != null)
{
secondArray.push(item);
}
}
Now i have seen this whole thing done in single line but cannot remember how it was done.
The result i am after is List of all objects containing that have ids 1,2,3.

You have to use Contains on testList:
var secondArray= db.Hero.Where (h=> testList.Contains(h.Id))

How about
var result = db.Hero.Where(x => testList.Contains(x.Id));
This would hit DB just once instead of 3 times.

sum of item prices that have the same item id

I want sum of all item prices in all rows in the database table that have the same item id. I mean the result should be one number and put it on textbox automatically when I choose a specific item id from dropdownlist
How can I do it in linq?
public double oIlstGetVouchersDetailjh(int nvoucherID)
{
Training_sNairoukhEntities1 sNairoukhEntities1 = new Training_sNairoukhEntities1();
double sum = (from Entity in sNairoukhEntities1.INV_InventoryItems
where Entity.ItemID == nvoucherID
select Entity.ItemPrice).sum();
return sum;
}
or
public double oIlstGetVouchersDetailjh(int nvoucherID)
{
Training_sNairoukhEntities1 sNairoukhEntities1 = new Training_sNairoukhEntities1();
double olstInvoicesSrech = from Entity in sNairoukhEntities1.INV_InventoryItems
group Entity by Entity.ItemID == nvoucherID into g
select g.sum(Entity => Entity.ItemPrice);
return olstInvoicesSrech;
}
but the second query give me this msg Cannot implicitly convert type 'System.Linq.IQueryable' to 'double

In your case, this will work:
Training_sNairoukhEntities1 sNairoukhEntities1 = new Training_sNairoukhEntities1();
double sum = (from Entity in sNairoukhEntities1.INV_InventoryItems
where Entity.ItemID == nvoucherID
select Entity.ItemPrice).Sum(); // Change sum to Sum
return sum;
Here's a simpler way:
sNairoukhEntities1.INV_InventoryItems.Where(item => item.ItemID == nvoucherID).Sum(item => item.ItemPrice);

Get list of child records

I have a database that looks like this:
tbl_Seminar
ID
isActive
tbl_SeminarFees
ID
seminar_id -- foreign key
fee_text
I want to get all seminars that are active (isActive ==1) and a list of the fees associated with that seminar. Each Seminar may have n records in tbl_SeminarFees that are its fees. I am able to return a linq structure that returns me a list of objects that look like this {seminar, SeminarFee} but I wanted to create a nested structure that looks like this:
{seminar, List<SeminarFee>}
What should my linq query look like?
here is my linq currently:
var results = from s in context.Seminar
join p in context.SeminarFees on
s.ID equals p.SeminarID
where s.IsActive == 1
select new
{
Seminar = s,
Fees = p
};
How do I change this to get a list of these: {seminar, List<SeminarFee>}
Thanks
UPDATE
#lazyberezovsky gave me a good idea to use a group join and into another variable. But then how do I loop through the result set. Here is what I have now:
foreach (var seminarAndItsFeesObject in results)
{
//do something with the seminar object
//do something with the list of fees
}
This however gives me the following error:
Argument type 'SeminarFees' does not match the
corresponding member type
'System.Collections.Generic.IEnumerable`1[SeminarFees]'
What am I doing wrong?
Thanks

You can use group join which groups inner sequence items based on keys equality (a.k.a. join..into) to get all fees related to seminar:
var results = from s in context.Seminar
join f in context.SeminarFees on
s.ID equals f.SeminarID into fees // here
where s.IsActive == 1
select new
{
Seminar = s,
Fees = fees
};
You can't call ToList() on server side. But you can map results on client later.
BTW You can define navigation property Fees on Seminar object:
public virtual ICollection<SeminarFee> Fees { get; set; }
In this case you will be able load seminars with fees:
var results = context.Seminar.Include(s => s.Fees) // eager loading
.Where(s => s.IsActive == 1);

var results = from s in context.Seminar
join p in context.SeminarFees on s.ID equals p.SeminarID
where s.IsActive == 1
group p by s into grouped
select new {
Seminar = grouped.Key,
Fees = grouped.ToList()
};

How to use LINQ-to-Entity to query by contained objects

Let's say I have a list of Boxes and in a box you can have multiple items.
Box (id)
Items (id, boxId)
I'm trying to build a linq to entity query that can return all the boxes that contains ALL specified items.
List<Box> FindBoxContainingAllSpecifiedItems(List<int> itemIds)
{
var q = from box in ctx.Boxes
where ???
}
Thanks for the help

It depends on the implementation of boxes. But lets for the moment say it has a property Items with the type IEnumerable<int>. In that case you could use the Intersect extension method to see if the items are all accounted for
var q = from box in ctx.Boxes
where box.Items.Intersect(itemIds).Count() == itemIds.Count;

Here is what I have found thanks to JaredPar contribution.
List<Location> FindLocationContainingAllItems(List<int> itemIds)
{
var itemQuery = from item in ctx.Items
select item;
// Workaround the Where In Clause (http://social.msdn.microsoft.com/Forums/en/adodotnetentityframework/thread/095745fe-dcf0-4142-b684-b7e4a1ab59f0)
itemQuery = itemQuery.Where(BuildContainExpression<Items, int>(i=> i.Id, itemIds));
int itemCount = itemIds.Count();
var locQuery = from loc in ctx.Locations
from box in loc.Boxes
where (from items in box.Items select items).Intersect(itemQuery).Count == itemCount
select loc;
return locQuery.ToList();
}