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Select data from 3 tables with Linq to SQL

I have 3 tables. Orders, OrderItems and OrderItemServices. Each order can contain multiple OrderItems and each OrderItem can contain multiple OrderItemServices.
I want to get a list of data of all orders from these tables in Linq. I could write a join but how do I make an anonymous data type to in select clasue which can give me Order list in this hierarchy?
If I use navigation properties and then select OrderItemServices in side select clause shown below it would fire individual select query for each OrderItemService which I want to avoid.
from order in Orders
select new
{
ActiveOrders = order,
ActiveOrderItems =order.OrderItems,
ActiveServices = order.OrderItems.Select(o => o.OrderItemServices)
}
Is it possible to group each order with a structure of multiple items inside it and multiple services inside items?

Refer msdn to start on LINQ To SQL
To get data from three tables you can get idea from the following simple example
var data = (from product in context.Products
from department in context.Departments
from category in context.Categories
where product.DeptId == department.DeptId
&& product.CatId == category.CatId
select new
{
product.Code,
product.Name,
department.Name,
category.Name
}).Distinct.ToList();

You have to set up your context to use eager loading:
var context = new MyDataContext();
var options = new DataLoadOptions();
options.LoadWith<Orders>(x => x.OrderItems);
options.LoadWith<OrderItems>(x => x.OrderItemServices);
context.LoadOptions = options;
var query = from order in context.Orders // ... etc
Then sub items will be included in initial query result and won't cause additional requests to the database. This will use JOIN internally to retrieve all the data in one go. You can check generated SQL using SQL Server Profiler.
http://blog.stevensanderson.com/2007/12/02/linq-to-sql-lazy-and-eager-loading-hiccups/

Linq To Entities, Select multiple sets of data with one query

I've found plenty of info on how to select multiple result sets with stored procedures but nothing substantial on how to do so with a linq query.
For example, I can do sub-queries that return mulitple sets of results with something like
var query = (from school in context.Schools
where school.id == someId
select new
{
subSetA = (from student in context.Students
select student).ToList(),
subSetB = (from building in context.Buildings
select building).ToList(),
}).First();
query.subSetA; //Access subSetA
query.subSetB; //Access subSetB
Which works fine, but what if I just want to select both subSetA and subSetB without querying against the school table? I want to select two separate sets of data that gets sent to the server in one query.
Any information as to how to do this with EF 6 would be great.

Well, I'm sure there are many ways to do this, but if you want to avoid introducing a third DbSet into the mix...
var query = (from s in context.Students.Take(1)
select new
{
subSetA = context.Students.ToList(),
subSetB = context.Buildings.ToList(),
})
Then, you can use query.ToList() or maybe using query.Load() and working with context.Students.Local, etc. would work.

LINQ Group by and having where clause

Below is the SQL Query I am trying to translate
SELECT dbo.Contracts.Supplier
FROM dbo.Contracts INNER JOIN dbo.Products ON dbo.Contracts.Product = dbo.Products.Product
where dbo.Products.ProductGroup='Crude'
GROUP BY dbo.Contracts.Supplier
Am I doing something wrong because I do not get same results with the following LINQ
var result = from c in context.Contracts
join p in context.Products on c.Product equals p.Product1
where p.Product1.Equals("Crude")
group c by c.Supplier into g
select new { supplier = g.Key };
It is generating a weird statement
SELECT
1 AS [C1],
[Distinct1].[Supplier] AS [Supplier]
FROM ( SELECT DISTINCT
[Extent1].[Supplier] AS [Supplier]
FROM [dbo].[Contracts] AS [Extent1]
WHERE N'Crude' = [Extent1].[Product]
) AS [Distinct1]
Using distinct would work but to get same results, LINQ should be generating a statement like so (it's like it is ignoring the join):
SELECT distinct dbo.Contracts.Supplier
FROM dbo.Contracts INNER JOIN dbo.Products ON dbo.Contracts.Product = dbo.Products.Product
where dbo.Products.ProductGroup='Crude'

I'm assuming that you are using 'EntityFramework' or 'Linq To SQL'. If so, you should be able to use navigation properties to navigate to product and filter invalit results out. This way your query might look something like this:
var result = (from c in context.Contracts
where c.Products.Any(p => p.ProductGroup == "Crude")
select c.Supplier).Distinct();
It will automatically convert into correct query (in this case possibly without join even, just using Exists sql keyword) and return distinct suppliers. This is if I understand your objective correctly - you want to obtain all suppliers assigned to contracts that contain product from 'Crude' product group.
Basically you should try to avoid using joins from linq to sql or linq to entities as much as possible when you can use navigation properties. System will probably be better at converting them into specific sql.

Is this LINQ Query "correct"?

I have the following LINQ query, that is returning the results that I expect, but it does not "feel" right.
Basically it is a left join. I need ALL records from the UserProfile table.
Then the LastWinnerDate is a single record from the winner table (possible multiple records) indicating the DateTime the last record was entered in that table for the user.
WinnerCount is the number of records for the user in the winner table (possible multiple records).
Video1 is basically a bool indicating there is, or is not a record for the user in the winner table matching on a third table Objective (should be 1 or 0 rows).
Quiz1 is same as Video 1 matching another record from Objective Table (should be 1 or 0 rows).
Video and Quiz is repeated 12 times because it is for a report to be displayed to a user listing all user records and indicate if they have met the objectives.
var objectiveIds = new List<int>();
objectiveIds.AddRange(GetObjectiveIds(objectiveName, false));
var q =
from up in MetaData.UserProfile
select new RankingDTO
{
UserId = up.UserID,
FirstName = up.FirstName,
LastName = up.LastName,
LastWinnerDate = (
from winner in MetaData.Winner
where objectiveIds.Contains(winner.ObjectiveID)
where winner.Active
where winner.UserID == up.UserID
orderby winner.CreatedOn descending
select winner.CreatedOn).First(),
WinnerCount = (
from winner in MetaData.Winner
where objectiveIds.Contains(winner.ObjectiveID)
where winner.Active
where winner.UserID == up.UserID
orderby winner.CreatedOn descending
select winner).Count(),
Video1 = (
from winner in MetaData.Winner
join o in MetaData.Objective on winner.ObjectiveID equals o.ObjectiveID
where o.ObjectiveNm == Constants.Promotions.SecVideo1
where winner.Active
where winner.UserID == up.UserID
select winner).Count(),
Quiz1 = (
from winner2 in MetaData.Winner
join o2 in MetaData.Objective on winner2.ObjectiveID equals o2.ObjectiveID
where o2.ObjectiveNm == Constants.Promotions.SecQuiz1
where winner2.Active
where winner2.UserID == up.UserID
select winner2).Count(),
};

You're repeating join winners table part several times. In order to avoid it you can break it into several consequent Selects. So instead of having one huge select, you can make two selects with lesser code. In your example I would first of all select winner2 variable before selecting other result properties:
var q1 =
from up in MetaData.UserProfile
select new {up,
winners = from winner in MetaData.Winner
where winner.Active
where winner.UserID == up.UserID
select winner};
var q = from upWinnerPair in q1
select new RankingDTO
{
UserId = upWinnerPair.up.UserID,
FirstName = upWinnerPair.up.FirstName,
LastName = upWinnerPair.up.LastName,
LastWinnerDate = /* Here you will have more simple and less repeatable code
using winners collection from "upWinnerPair.winners"*/

The query itself is pretty simple: just a main outer query and a series of subselects to retrieve actual column data. While it's not the most efficient means of querying the data you're after (joins and using windowing functions will likely get you better performance), it's the only real way to represent that query using either the query or expression syntax (windowing functions in SQL have no mapping in LINQ or the LINQ-supporting extension methods).
Note that you aren't doing any actual outer joins (left or right) in your code; you're creating subqueries to retrieve the column data. It might be worth looking at the actual SQL being generated by your query. You don't specify which ORM you're using (which would determine how to examine it client-side) or which database you're using (which would determine how to examine it server-side).
If you're using the ADO.NET Entity Framework, you can cast your query to an ObjectQuery and call ToTraceString().
If you're using SQL Server, you can use SQL Server Profiler (assuming you have access to it) to view the SQL being executed, or you can run a trace manually to do the same thing.
To perform an outer join in LINQ query syntax, do this:
Assuming we have two sources alpha and beta, each having a common Id property, you can select from alpha and perform a left join on beta in this way:
from a in alpha
join btemp in beta on a.Id equals btemp.Id into bleft
from b in bleft.DefaultIfEmpty()
select new { IdA = a.Id, IdB = b.Id }
Admittedly, the syntax is a little oblique. Nonetheless, it works and will be translated into something like this in SQL:
select
a.Id as IdA,
b.Id as Idb
from alpha a
left join beta b on a.Id = b.Id

It looks fine to me, though I could see why the multiple sub-queries could trigger inefficiency worries in the eyes of a coder.
Take a look at what SQL is produced though (I'm guessing you're running this against a database source from your saying "table" above), before you start worrying about that. The query providers can be pretty good at producing nice efficient SQL that in turn produces a good underlying database query, and if that's happening, then happy days (it will also give you another view on being sure of the correctness).

Combine two or more table into one object

I need to combine two or more table into one object by using C# 4,0... I wrote a class for a table which included simple select selectbyid insert update and update.... it works fine for single table... by the way I have two attribute which specifies table name column name and primarykey... by using all these I can create my simple methods but I need to select and update more table in one object or method... what should I do or what would you suggest about it...
Example:
users and customer table I have foreign keys which defined...

If you`re using linq to sql, you can join the other tables like
var q =
from s in db.Suppliers
join c in db.Customers on s.City equals c.City
select new {
Supplier = s.CompanyName,
Customer = c.CompanyName,
City = c.City
};
as just copy & paste from a sample of MSDN LINQ to SQL: .NET Language-Integrated Query for Relational Data