The DataContext

The DataContext is the main conduit by which you retrieve objects from the database and resubmit changes. You use it in the same way that you would use an ADO.NET Connection. In fact, the DataContext is initialized with a connection or connection string you supply. The purpose of the DataContext is to translate your requests for objects into SQL queries made against the database and then assemble objects out of the results. The DataContext enables language-integrated query by implementing the same operator pattern as the standard query operators such as Where and Select.

For example, you can use the DataContext to retrieve customer objects whose city is London as follows:

C#

// DataContext takes a connection string 
DataContext db = new   DataContext("c:\\northwind\\northwnd.mdf");
// Get a typed table to run queries
Table Customers = db.GetTable();
// Query for customers from London
var q =
   from c in Customers
   where c.City == "London"
   select c;
foreach (var cust in q)
   Console.WriteLine("id = {0}, City = {1}", cust.CustomerID, cust.City);

Visual Basic

' DataContext takes a connection string 
Dim db As DataContext  = New DataContext("c:\northwind\northwnd.mdf")
' Get a typed table to run queries
Dim Customers As Customers(Of Customer) = db.GetTable(Of Customer)()
' Query for customers from London
Dim londonCustomers = From customer in Customers _
                      Where customer.City = "London" _
                      Select customer
For Each cust in londonCustomers
   Console.WriteLine("id = " & cust.CustomerID & ", City = " & cust.City)
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