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Cannot include child table after GroupBy

I have two related tables:
OrderHeader
Id
Truck_name
Group
OrderItem
Id
OrderID
Location
Read
OrderItem contains column OrderHeaderId (foreign key relationship).
My WebService has to select specific Order with orderItems and return it(after some parsing) to client. I have to use eager loading because of important data in OrderItem.My database query needs to load first not finished (Status IN 1402,1403 AND Read=0) order. So:
context.Configuration.LazyLoadingEnabled = false;
var query = context.OrderHeader
.Where(o=> new[] { 1402, 1403 }.Contains(o.Status) && o.OrderItem.Any(g => g.Read == 0))
.OrderBy(o => o.Id)
.GroupBy(g => g.Group)
.FirstOrDefault()
.AsQueryable()
.Include("OrderItem");
I use GroupBy to take first not finished Group and every time it returns me an empty OrderItem table. Why? How to include child table after GroupBy statement?

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/

Conditional LINQ query on self-joining table with 2 sets of data

I am trying to figure out how to perform a conditional query on an Employees table to bring back all of their assigned Projects, but the caveat I don't quite understand on how to implement is that for every Employee, there is 0 to 1 EmployeeAssistant (self-joining entity). So when I select EmployeeID=2 and it has an EmployeeAssistantID=5, I would like to display all of the Projects for both of these individuals, i.e. the main Employee (EmployeeID=2) and their assistant (EmployeeID=5).
The tables look like:
Employees
- EmployeeID -- (Pkey)
- EmployeeAssistantID -- (Fkey to Employees.EmployeeID)
- other fields
-
Projects
- ProjectID -- (PKey)
- EmployeeID -- (Fkey to Employees.EmployeeID)
- other fields
I attempted the following in LINQ:
var projects = Projects.Include(proj => proj.Employee)
.Select(x => new
{
proj.ProjectID,
proj.ProjectName,
proj.Employee.Name
// ... not sure how to bring back another layer of projects for the EmployeeAssistant?
})

You can use the following Linq query to get the data you want:
var query = from e in Employees
join a in Employees on e.EmployeeAssistantID equals a.EmployeeID
where e.EmployeeID == 2
select new
{
EmployeeID = e.EmployeeID,
AssistantID = a.EmployeeID,
EmployeeProjects = Projects.Where(p => p.EmployeeID == e.EmployeeID),
AssistantProjects = Projects.Where(p => p.EmployeeID == a.EmployeeID)
};
The anonymous type returned by the query contains all of the data from both employee entities, as well as all of the Project data of each employee (some can be the same, others might differ).

I believe you mean to do the following:
var employeeIDs = new[] { myEmployee.EmployeeID, myEmployee.EmployeeAssistantID };
var projects = Projects.Where(p => employeeIds.Contains(p.EmployeeID));
This will grab all projects that both the employee and the assistant have done, given a previously grabbed Employee record (which I've called myEmployee).

Linq select Item where it is equal to ID in another table

I am not sure how possible this is but I have two tables and I want to grab a value from table 2 via the value of table 1.
Table 1 has the a Foreign Key called "rank" which is an int. Table 2 has a value called "name" which is a string. Now Table 1's "rank" correlates to Table 2's "ID".
So when I say
var result =
db.Table1.Select(x => new { x.name, x.rank }).ToList();
//Bob - 2
I really want to say something like
var result =
db.Table1.Select(x => new { x.name, Table2.rank.Where(ID == x.rank) }).ToList();
//Bob - Gold
I am still new to LINQ though and I am not sure how to get rank's string value from the other table within a query like this.
EDIT
Tables I am using and their relational values.
User: ID (PK), s1elo (FK to PastElos), champ (FK to ChampionList), elo (FK to EloList)
PastElo: ID (PK), Rank
ChampionList: ID (PK), name
EloList: ID (PK), Rank
Working example for Users and PastElo
var result =
db.Users.Join(db.PastEloes,
x => x.s1elo, y => y.ID, (x, y)
=> new { y.Rank, x.name, x.other_items_in_Users }).ToList();
Note: PastElo is PastEloe's due to EF making everything plural when I synced up my DB, thus why User is also Users, I think that is referred to as the "context".

You could try something like the following:
var result = db.Table1.Join(db.Table2,
x=>x.rank,
y=>y.ID,
(x,y) => new { x.rank, y.Name }).ToList();
In the above linq query we make a Join between the two tables, Table1 and Table2 based on the association and then we select that we want.
Another way you could try to write this query would be the following:
var result = (from t1 in db.Table1
join t2 in db.Table2
on t1.rank equals t2.ID
select new { t1.rank, t2.Name, }).ToList();

Another way to do this would be to include your Database relationships in your C# entities. You could use EntityRef here. See the following documentation:
https://learn.microsoft.com/en-us/dotnet/framework/data/adonet/sql/linq/how-to-map-database-relationships

Linq List Contains Method

Im newbie to linq and im using linq query to retrieve data from the table.My idea is to list all the cashsafes corresponding to a particular user and show it in dropdownlist.
The table structure is shown below
Table 1
cashsafeid cashsafename
1 cashsafe1
2 cashsafe2
3 cashsafe3
Table 2
Id UserId Cashsafeid
1 100 1,2,3
2 101 1,3
I've to get the cashsafename of a particular user say 100.How can i achieve it
The below code is the one i've tried but am stuck
List<Cashsafe> cashsafes=(from c in db.Table 1
where c.CashsafeId contains() )--Cannot go further

You store User's Cachsafeid column in very inefficient way - it doesn't allow to generate efficient SQL for LINQ provider. So the following solution has bad performance - if you care about that - change your table structure.
var user = db.Table2.Single(u => u.UserId == 100);
var cachfeIds = user.Cashsafeid.Split(',').Select(int.Parse).ToArray();
var cachefes = db.Table1.Where(c => cachfeIds.Contains(c.Id)).ToList();
Basically you need to join to tables, but foreign key is "virtual" - it is only in your mind. To retrieve foreign key values we must split the Cachsafeid column's value of every user to retrieve linked cachefes. And only then retrieve the cachefes with separate request (I think LINQ will retrieve all values from table and the execute Where part in C# code).

if you have no idea of join you can use
int x = 0;
List<int> Users = db.table2.FirstOrDefault(m => m.UserId == 100).Cashsafeid.Split(',').ToList().Where(str => int.TryParse(str, out x)).Select(str => x).ToList(); ;
var content = db.table1.Where(m => Users.Contains(m.cashsafeid)).ToList();