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C# Learning: LINQ to SQL(First Example)


The first step in building a LINQ to SQL application is declaring the classes we’ll
use to represent your application data: our entities.


[Table(Name="Contacts")]
class Contact
{
[Column(IsPrimaryKey=true)]
public int ContactID { get; set; }
[Column(Name="ContactName"]
public string Name { get; set; }
[Column]
public string City { get; set; }
}


The next thing we need to prepare before being able to use language-integrated
queries is a System.Data.Linq.DataContext object. The purpose of DataContext

is to translate requests for objects into SQL queries made against the database and
then assemble objects out of the results.

The full example below,

using System;
using System.Linq;
using System.Data.Linq;
using System.Data.Linq.Mapping;
static class HelloLinqToSql

{

static void Main()
{
string path =
System.IO.Path.GetFullPath(@"..\..\..\..\Data\northwnd.mdf");
DataContext db = new DataContext(path);



var contacts =
from contact in db.GetTable<Contact>()
where contact.City == "Paris"
select contact;

foreach (var contact in contacts)
Console.WriteLine("Bonjour "+contact.Name);
}
}


Notice how easy it is to get strongly typed access to a database thanks to LINQ.
This is a simplistic example, but it gives you a good idea of what LINQ to SQL has
to offer and how it could change the way you work with databases.
Let’s sum up what has been done automatically for us by LINQ to SQL:
■ Opening a connection to the database
■ Generating the SQL query
■ Executing the SQL query against the database
■ Creating and filling our objects out of the tabular results


You’ll notice the following things in the old-school
code when comparing it with our LINQ to SQL code:
■ Queries explicitly written SQL in quotes
■ No compile-time checks
■ Loosely bound parameters
■ Loosely typed result sets
■ More code required
■ More knowledge required





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