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C# - Join Syntax with two tables [duplicate]

I'm writing a LINQ to SQL statement, and I'm after the standard syntax for a normal inner join with an ON clause in C#.
How do you represent the following in LINQ to SQL:
select DealerContact.*
from Dealer
inner join DealerContact on Dealer.DealerID = DealerContact.DealerID

It goes something like:
from t1 in db.Table1
join t2 in db.Table2 on t1.field equals t2.field
select new { t1.field2, t2.field3}
It would be nice to have sensible names and fields for your tables for a better example. :)
Update
I think for your query this might be more appropriate:
var dealercontacts = from contact in DealerContact
join dealer in Dealer on contact.DealerId equals dealer.ID
select contact;
Since you are looking for the contacts, not the dealers.

And because I prefer the expression chain syntax, here is how you do it with that:
var dealerContracts = DealerContact.Join(Dealer,
contact => contact.DealerId,
dealer => dealer.DealerId,
(contact, dealer) => contact);

To extend the expression chain syntax answer by Clever Human:
If you wanted to do things (like filter or select) on fields from both tables being joined together -- instead on just one of those two tables -- you could create a new object in the lambda expression of the final parameter to the Join method incorporating both of those tables, for example:
var dealerInfo = DealerContact.Join(Dealer,
dc => dc.DealerId,
d => d.DealerId,
(dc, d) => new { DealerContact = dc, Dealer = d })
.Where(dc_d => dc_d.Dealer.FirstName == "Glenn"
&& dc_d.DealerContact.City == "Chicago")
.Select(dc_d => new {
dc_d.Dealer.DealerID,
dc_d.Dealer.FirstName,
dc_d.Dealer.LastName,
dc_d.DealerContact.City,
dc_d.DealerContact.State });
The interesting part is the lambda expression in line 4 of that example:
(dc, d) => new { DealerContact = dc, Dealer = d }
...where we construct a new anonymous-type object which has as properties the DealerContact and Dealer records, along with all of their fields.
We can then use fields from those records as we filter and select the results, as demonstrated by the remainder of the example, which uses dc_d as a name for the anonymous object we built which has both the DealerContact and Dealer records as its properties.

var results = from c in db.Companies
join cn in db.Countries on c.CountryID equals cn.ID
join ct in db.Cities on c.CityID equals ct.ID
join sect in db.Sectors on c.SectorID equals sect.ID
where (c.CountryID == cn.ID) && (c.CityID == ct.ID) && (c.SectorID == company.SectorID) && (company.SectorID == sect.ID)
select new { country = cn.Name, city = ct.Name, c.ID, c.Name, c.Address1, c.Address2, c.Address3, c.CountryID, c.CityID, c.Region, c.PostCode, c.Telephone, c.Website, c.SectorID, Status = (ContactStatus)c.StatusID, sector = sect.Name };
return results.ToList();

You create a foreign key, and LINQ-to-SQL creates navigation properties for you. Each Dealer will then have a collection of DealerContacts which you can select, filter, and manipulate.
from contact in dealer.DealerContacts select contact
or
context.Dealers.Select(d => d.DealerContacts)
If you're not using navigation properties, you're missing out one of the main benefits on LINQ-to-SQL - the part that maps the object graph.

Use Linq Join operator:
var q = from d in Dealer
join dc in DealerConact on d.DealerID equals dc.DealerID
select dc;

basically LINQ join operator provides no benefit for SQL. I.e. the following query
var r = from dealer in db.Dealers
from contact in db.DealerContact
where dealer.DealerID == contact.DealerID
select dealerContact;
will result in INNER JOIN in SQL
join is useful for IEnumerable<> because it is more efficient:
from contact in db.DealerContact
clause would be re-executed for every dealer
But for IQueryable<> it is not the case. Also join is less flexible.

Actually, often it is better not to join, in linq that is. When there are navigation properties a very succinct way to write your linq statement is:
from dealer in db.Dealers
from contact in dealer.DealerContacts
select new { whatever you need from dealer or contact }
It translates to a where clause:
SELECT <columns>
FROM Dealer, DealerContact
WHERE Dealer.DealerID = DealerContact.DealerID

Inner join two tables in linq C#
var result = from q1 in table1
join q2 in table2
on q1.Customer_Id equals q2.Customer_Id
select new { q1.Name, q1.Mobile, q2.Purchase, q2.Dates }

Use LINQ joins to perform Inner Join.
var employeeInfo = from emp in db.Employees
join dept in db.Departments
on emp.Eid equals dept.Eid
select new
{
emp.Ename,
dept.Dname,
emp.Elocation
};

Try this :
var data =(from t1 in dataContext.Table1 join
t2 in dataContext.Table2 on
t1.field equals t2.field
orderby t1.Id select t1).ToList();

OperationDataContext odDataContext = new OperationDataContext();
var studentInfo = from student in odDataContext.STUDENTs
join course in odDataContext.COURSEs
on student.course_id equals course.course_id
select new { student.student_name, student.student_city, course.course_name, course.course_desc };
Where student and course tables have primary key and foreign key relationship

try instead this,
var dealer = from d in Dealer
join dc in DealerContact on d.DealerID equals dc.DealerID
select d;

var Data= (from dealer in Dealer join dealercontact in DealerContact on dealer.ID equals dealercontact.DealerID
select new{
dealer.Id,
dealercontact.ContactName
}).ToList();

var data=(from t in db.your tableName(t1)
join s in db.yourothertablename(t2) on t1.fieldname equals t2.feldname
(where condtion)).tolist();

var list = (from u in db.Users join c in db.Customers on u.CustomerId equals c.CustomerId where u.Username == username
select new {u.UserId, u.CustomerId, u.ClientId, u.RoleId, u.Username, u.Email, u.Password, u.Salt, u.Hint1, u.Hint2, u.Hint3, u.Locked, u.Active,c.ProfilePic}).First();
Write table names you want, and initialize the select to get the result of fields.

from d1 in DealerContrac join d2 in DealerContrac on d1.dealearid equals d2.dealerid select new {dealercontract.*}

One Best example
Table Names : TBL_Emp and TBL_Dep
var result = from emp in TBL_Emp join dep in TBL_Dep on emp.id=dep.id
select new
{
emp.Name;
emp.Address
dep.Department_Name
}
foreach(char item in result)
{ // to do}

LINQ Unable to get distinct value from many to many Entity Framework

I am using linq to query many to many relationship
I have those tables/entities :
Each order has multiple products and I want to get distinct order with products.
Here is my query:
var query = (from order in db.Order
join orderproduct in db.OrderProduct
on order.orderId equals orderproduct.OrderId
join product in db.Product
on orderproduct.ProductId equals product.productId
select new
{ order.orderId,
order.name,
product.productId,
product.productName,
product.price
}).Distinct().ToList();
This is the result :
I want to get only name "Jane" with 2 products. The result is showed 2 records with same name "Jane".
How to get one record name "jane" and 2 products?
Thanks for your help.

use the following:
var query = (from order in db.Order
join orderproduct in db.OrderProduct
on order.orderId equals orderproduct.OrderId
join product in db.Product
on orderproduct.ProductId equals product.productId
select new {order.orderId,order.name,product.productId,product.productName,product.price}).GroupBy(order=>order.orderId).ToList();

If you want to return a structure containing the customer's name and its ordered products, I recommend to group the products by order.orderName (not order.orderId) and to load the result into a dictionary:
var query = from order in db.Order
join orderproduct in db.OrderProduct on order.orderId equals orderproduct.OrderId
join product in db.Product on orderproduct.ProductId equals product.productId
group product by order.orderName into orderGroup
select orderGroup;
var orderedProductsByName = query.ToDictionary(name => name.Key, products => products.ToList());

convert this into linq or lambda c#

Can someone please help me convert this SQL to linq or lambda c#
select
count(s.ClassId) [StudentInClass], c.Name [Class], t.Name [teacher]
from
[dbo].[Students] s
inner join
class c on s.ClassId = c.Id
inner join Teacher t
on t.Id = c.TeacherId
group by
s.ClassId, c.Name, t.Name
so far this is what I have, and i am messing it up. I want to achieve the same results as in my sql query
SchoolEntities db = new SchoolEntities();
var StudentsByCourseId = from s in db.Students
join c in db.Classes on s.ClassId equals c.Id
join t in db.Teachers on c.TeacherId equals t.Id
group c by s.ClassId
into g
select g;
in SQL this is what my reults look like, it counts the students in a class by the teacher
StudentCount Class Teacher
1 Geography Teacher1
1 Biology Teacher1
2 Maths Teacher2

You can use an anonymous class to group by multiple properties.
var StudentsByCourseId = from s in db.Students
join c in db.Classes on s.ClassId equals c.Id
join t in db.Teachers on c.TeacherId equals t.Id
group s by new { s.ClassId, Class = c.Name, Teacher = t.Name }
into g
select new
{
StudentInClass = g.Count(),
g.Key.Class,
g.Key.Teacher,
};

Alternative to nesting when performing a left join and multiple inner joins

Consider the following fictitious scenario:
How would I go about getting a list of all the categories (distinct or otherwise, it doesn't matter) for each customer, even if a customer hasn't ordered any products?
Also assume that we don't have navigation properties, so we'll need to use manual joins.
This is my attempt which uses nesting:
var customerCategories = from c in context.Customers
join o in context.Orders on c.CustomerId equals o.CustomerId into orders
select new
{
CustomerName = c.Name,
Categories = (from o in orders
join p in context.Products on o.ProductId equals p.ProductId
join cat in context.Category on p.CategoryId equals cat.CategoryId
select cat)
};
Is there a different (possibly better way) to achieve the same outcome?
Alternative: Multiple Left (Group) Joins
var customerCategories = from customer in context.Customers
join o in context.Orders on customer.CustomerId equals o.CustomerId into orders
from order in orders.DefaultIfEmpty()
join p in context.Products on order.ProductId equals p.ProductId into products
from product in products.DefaultIfEmpty()
join cat in context.Categories on product.CategoryId equals cat.CategoryId into categories
select new
{
CustomerName = c.Name,
Categories = categories
};

I recreated your table structure and added some data so that I could get a better idea what you were trying to do. I found a couple of ways to accomplish what you want but I'm just going to add this method. I think it's the most concise and I think it's pretty clear.
Code
var summaries = Customers.GroupJoin(Orders,
cst => cst.Id,
ord => ord.CustomerId,
(cst, ord) => new { Customer = cst, Orders = ord.DefaultIfEmpty() })
.SelectMany(c => c.Orders.Select(o => new
{
CustomerId = c.Customer.Id,
CustomerName = c.Customer.Name,
Categories = Categories.Where(cat => cat.Id == c.Customer.Id)
}));
Output
Table Structure
Table Data

If you need all categories couldn't you just:
Categories = (from c in context.Category
select cat)

How to select CompanyName and number of its products?

I want to write a Linq query that will return, columns with CompanyName of Supplier and number of all products of this company. Can you help me?
So far I got this:
var company = from pro in db.Products
join sup in db.Suppliers
on pro.SupplierID equals sup.SupplierID
group pro by pro.SupplierID
into g
select new { Name = g.Key, COUNT = g.Count() };
But this returns SupplierID not CompanyName. Database is Northwnd.

Use group join (i.e. join...into) to join suppliers with products and get all products of supplier in group:
from s in db.Suppliers
join p in db.Products
on s.SupplierID equals p.SupplierID into g
select new {
s.CompanyName,
ProductsCount = g.Count()
}

The following compiles and runs with Linq-for-objects. I can't vouch for whether Linq-to-SQL will cope.
var company = from sup in db.Suppliers
select new
{
Name = sup.CompanyName,
COUNT = db.Products
.Where(pro => pro.SupplierID == sup.SupplierID)
.Count()
};