LINQ to SharePoint Provider

The gateway class for the LINQ to SharePoint provider is Microsoft.SharePoint.Linq.DataContext which represents the data of a SharePoint Foundation Web site. 

It is parallel in use and function to the System.Data.Linq.DataContext class in the LINQ to SQL provider. 

Just as the latter class has a GetTable() method that returns a Table<TEntity> object that implements System.Linq.IQueryable<T>, so too, the Microsoft.SharePoint.Linq.DataContext class has a GetList<T>method that returns an EntityList<TEntity> class that implements System.Linq.IQueryable<T>. 

It is objects of type EntityList<TEntity> that are queried.

The following is an example of the use of LINQ to query SharePoint Foundation.

// Get DataContext from page context
DataContext data = new DataContext(SPContext.Current.Web.Url);

// Get the SharePoint list
EntityList<Customer> Customers = data.GetList<Customer>("Customers");

// Query for customers from London
var londonCustomers = from customer in Customers
                      where customer.City == "London"
                      select customer;

foreach (var londonCust in londonCustomers)
{
    Console.Writeline("id = {0}, City = {1}", 
                      londonCust.CustomerId, 
                      londonCust.City);
}

The following is an example of using LINQ to add an item to a SharePoint Foundation list.
// Get DataContext from page context
DataContext data = new DataContext(SPContext.Current.Web.Url);

// Get the SharePoint list
EntityList<Customer> Customers = data.GetList<Customer>("Customers");

// Create the item to be added
Customer newCustomer = new Customer() { CustomerId=36, City=”Madrid” };

// Mark the item to be added on the next call of Submit
Customers.InsertOnSubmit(newCustomer);

// Submit all changes
data.SubmitChanges();