1.) 手工书写代码，自定义需要映射的表和关系

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data.Linq; //DataContext在此命名空间下
using System.Data.Linq.Mapping; //[Database] [Tabale] 等属性在此命名空间下

namespace LinqConsole
{
    [Database(Name = "Northwind")]
    class MyContext : DataContext
    {
        public MyContext(string conStr)
            : base(conStr)
        { }

        // MyContext中唯一的表，Orders利用Association关联，MyContext中并没有保留Orders的信息
        public Table<MyCustomer> Customers;
    }

    [Table(Name = "Customers")]
    public class MyCustomer
    {
        [Column(IsPrimaryKey = true)]
        public string CustomerID;

        [Column]
        public string CompanyName;

        [Column]
        public string Country;

        [Association(ThisKey = "CustomerID", OtherKey = "CustomerID")]
        public EntitySet<MyOrder> Orders; 
    }

    [Table(Name = "Orders")]
    public class MyOrder
    {
        [Column(IsPrimaryKey = true)]
        public int OrderID;

        [Column]
        public string CustomerID;
    }

    class Program
    {
        static void Main(string[] args)
        {
            MyContext ctx = new MyContext("server=.");

            var query = from c in ctx.Customers
                        select c;

            foreach (MyCustomer c in query)
            {
                Console.WriteLine("{0},{1},{2}", c.CustomerID, c.CompanyName, c.Country);
          
                //通过Customer表中的 Association 获得Orders表中数据
                Console.WriteLine(c.Orders.Count);
            }

        }
    }
}

>sqlmetal /?
Microsoft (R) Database Mapping Generator 2008 Beta 2 version 1.00.20706
for Microsoft (R) .NET Framework version 3.5
Copyright (C) Microsoft Corporation. All rights reserved.

SqlMetal [options] [<input file>]

  Generates code and mapping for the LINQ to SQL component of the .NET framework. SqlMetal can:
  - Generate source code and mapping attributes or a mapping file from a database.
  - Generate an intermediate dbml file for customization from the database.
  - Generate code and mapping attributes or mapping file from a dbml file.

Options:
  /server:<name>             Database server name.
  /database:<name>           Database catalog on server.
  /user:<name>               Login user ID (default: use Windows Authentication).
  /password:<password>       Login password (default: use Windows Authentication).
  /conn:<connection string>  Database connection string. Cannot be used with /server, /database, /user or /password option
  /timeout:<seconds>         Timeout value to use when SqlMetal accesses the database (default: 0 which means infinite).

  /views                     Extract database views.
  /functions                 Extract database functions.
  /sprocs                    Extract stored procedures.

  /dbml[:file]               Output as dbml. Cannot be used with /map option.
  /code[:file]               Output as source code. Cannot be used with /dbml option.
  /map[:file]                Generate mapping file, not attributes. Cannot be used with /dbml option.

  /language:<language>       Language for source code: VB or C# (default: derived from extension on code file name).
  /namespace:<name>          Namespace of generated code (default: no namespace).
  /context:<type>            Name of data context class (default: derived from database name).
  /entitybase:<type>         Base class of entity classes in the generated code (default: entities have no base class).
  /pluralize                 Automatically pluralize or singularize class and member names using English language rules.
  /serialization:<option>    Generate serializable classes: None or Unidirectional (default: None).
  /provider:<type>           Provider type (default: provider is determined at run time).

  <input file>               May be a SqlExpress mdf file, a SqlCE sdf file, or a dbml intermediate file.

Create code from SqlServer:
  SqlMetal /server:myserver /database:northwind /code:nwind.cs /namespace:nwind

Generate intermediate dbml file from SqlServer:
  SqlMetal /server:myserver /database:northwind /dbml:northwind.dbml /namespace:nwind

Generate code with external mapping from dbml:
  SqlMetal /code:nwind.cs /map:nwind.map northwind.dbml

Generate dbml from a SqlCE sdf file:
  SqlMetal /dbml:northwind.dbml northwind.sdf

Generate dbml from SqlExpress local server:
  SqlMetal /server:.\sqlexpress /database:northwind /dbml:northwind.dbml

Generate dbml by using a connection string in the command line:
  SqlMetal /conn:"server='myserver'; database='northwind'" /dbml:northwind.dbml

    生成Northwind库，生成的代码为mapping.cs，添加入Vs2008就可以直接使用生成的类、方法：

>sqlmetal /server:. /database:northwind /code:mapping.cs /language:csharp
Microsoft (R) Database Mapping Generator 2008 Beta 2 version 1.00.20706
for Microsoft (R) .NET Framework version 3.5
Copyright (C) Microsoft Corporation. All rights reserved.

      3.) 使用Sqlmetal生成映射文件.xml

>sqlmetal /server:. /database:northwind /map:mapping.xml

     生成mapping.xml文件，部分如下：（只需要Prodcuts表和Orders表）

<?xml version="1.0" encoding="utf-8"?>
<Database Name="northwind" xmlns="http://schemas.microsoft.com/linqtosql/mapping/2007">
  <Table Name="dbo.Customers" Member="Customers">
    <Type Name="Customers">
      <Column Name="CustomerID" Member="CustomerID" Storage="_CustomerID" DbType="NChar(5) NOT NULL" CanBeNull="false" IsPrimaryKey="true" />
      <Column Name="CompanyName" Member="CompanyName" Storage="_CompanyName" DbType="NVarChar(40) NOT NULL" CanBeNull="false" />
      <Column Name="ContactName" Member="ContactName" Storage="_ContactName" DbType="NVarChar(30)" />
      <Column Name="ContactTitle" Member="ContactTitle" Storage="_ContactTitle" DbType="NVarChar(30)" />
      <Column Name="Address" Member="Address" Storage="_Address" DbType="NVarChar(60)" />
      <Column Name="City" Member="City" Storage="_City" DbType="NVarChar(15)" />
      <Column Name="Region" Member="Region" Storage="_Region" DbType="NVarChar(15)" />
      <Column Name="PostalCode" Member="PostalCode" Storage="_PostalCode" DbType="NVarChar(10)" />
      <Column Name="Country" Member="Country" Storage="_Country" DbType="NVarChar(15)" />
      <Column Name="Phone" Member="Phone" Storage="_Phone" DbType="NVarChar(24)" />
      <Column Name="Fax" Member="Fax" Storage="_Fax" DbType="NVarChar(24)" />
      <Association Name="FK_CustomerCustomerDemo_Customers" Member="CustomerCustomerDemo" Storage="_CustomerCustomerDemo" ThisKey="CustomerID" OtherKey="CustomerID" DeleteRule="NO ACTION" />
      <Association Name="FK_Orders_Customers" Member="Orders" Storage="_Orders" ThisKey="CustomerID" OtherKey="CustomerID" DeleteRule="NO ACTION" />
    </Type>
  </Table>
  <Table Name="dbo.Orders" Member="Orders">
    <Type Name="Orders">
      <Column Name="OrderID" Member="OrderID" Storage="_OrderID" DbType="Int NOT NULL IDENTITY" IsPrimaryKey="true" IsDbGenerated="true" AutoSync="OnInsert" />
      <Column Name="CustomerID" Member="CustomerID" Storage="_CustomerID" DbType="NChar(5)" />
      <Column Name="EmployeeID" Member="EmployeeID" Storage="_EmployeeID" DbType="Int" />
      <Column Name="OrderDate" Member="OrderDate" Storage="_OrderDate" DbType="DateTime" />
      <Column Name="RequiredDate" Member="RequiredDate" Storage="_RequiredDate" DbType="DateTime" />
      <Column Name="ShippedDate" Member="ShippedDate" Storage="_ShippedDate" DbType="DateTime" />
      <Column Name="ShipVia" Member="ShipVia" Storage="_ShipVia" DbType="Int" />
      <Column Name="Freight" Member="Freight" Storage="_Freight" DbType="Money" />
      <Column Name="ShipName" Member="ShipName" Storage="_ShipName" DbType="NVarChar(40)" />
      <Column Name="ShipAddress" Member="ShipAddress" Storage="_ShipAddress" DbType="NVarChar(60)" />
      <Column Name="ShipCity" Member="ShipCity" Storage="_ShipCity" DbType="NVarChar(15)" />
      <Column Name="ShipRegion" Member="ShipRegion" Storage="_ShipRegion" DbType="NVarChar(15)" />
      <Column Name="ShipPostalCode" Member="ShipPostalCode" Storage="_ShipPostalCode" DbType="NVarChar(10)" />
      <Column Name="ShipCountry" Member="ShipCountry" Storage="_ShipCountry" DbType="NVarChar(15)" />
      <Association Name="FK_Order_Details_Orders" Member="OrderDetails" Storage="_OrderDetails" ThisKey="OrderID" OtherKey="OrderID" DeleteRule="NO ACTION" />
      <Association Name="FK_Orders_Customers" Member="Customers" Storage="_Customers" ThisKey="CustomerID" OtherKey="CustomerID" IsForeignKey="true" />
      <Association Name="FK_Orders_Employees" Member="Employees" Storage="_Employees" ThisKey="EmployeeID" OtherKey="EmployeeID" IsForeignKey="true" />
      <Association Name="FK_Orders_Shippers" Member="Shippers" Storage="_Shippers" ThisKey="ShipVia" OtherKey="ShipperID" IsForeignKey="true" />
    </Type>
  </Table>
</Database>

      相关CS代码如下：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data.Linq;
using System.Data.Linq.Mapping;

namespace LinqConsole
{
    class MyContext : DataContext
    {
        public MyContext(string conStr, MappingSource source)
            : base(conStr, source)
        {
        }
    }

    public class Customers
    {
        private string _CustomerID;
        public string CustomerID { get{return _CustomerID;} set{_CustomerID=value;} }
    }

    class Program
    {
        static void Main(string[] args)
        {
            DataContext ctx = new DataContext("server=.database=northwind", XmlMappingSource.FromUrl("mapping.xml"));

            var query = from c in ctx.GetTable<Customers>()
                        select c;

            foreach (Customers c in query)
            {
                Console.WriteLine("{0},{1},{2}", c.CustomerID);
            }

        }
    }
}