Sanjeetosphere : C# 3.0

How To: Use SqlMetal.exe to Create a Class from XML and Database

Sanjeet — Thu, 07 Jun 2007 11:23:48 GMT

If you don't have Visual C# Codename Orcas Express Edition installed on your development machine, and you are using Visual Studio 2005 with the LINQ 2006 CTP, then SqlMetal.exe is something that you must lookout for.

It is the O/R mapper that you must use to create a strongly typed class, and use it with DLinq.

You can find SqlMetal.exe at: %systemdrive%\Program Files\LINQ Preview\Bin folder.

Its used as following:

usage: sqlmetal [options] [<input file>]
options:
  /server:<name>     database server name
  /database:<name>   database catalog on server
  /user:<name>       login user id
  /password:<name>   login password
  /views             extract database views
  /functions         extract database functions
  /sprocs            extract stored procedures
  /xml[:file]        output as xml
  /code[:file]       output as source code
  /map[:file]        generate xml mapping file instead of attributes
  /language:xxx      language for source code (vb,csharp)
  /namespace:<name>  namespace used for source code
  /pluralize         auto-pluralize table names
  /dataAttributes    auto-generate DataObjectField and Precision attributes
  /timeout:<seconds> timeout value in seconds to use for database commands

examples:
To generate an XML file with extracted SQL metadata
  sqlmetal /server:myserver /database:northwind /xml:mymeta.xml

To generate an XML file with extracted SQL metadata from an .mdf file
  sqlmetal /xml:mymeta.xml mydbfile.mdf

To generate source code from an XML metadata file
  sqlmetal /namespace:nwind /code:nwind.cs /language:csharp mymetal.xml

To generate source code from SQL metadata directly
  sqlmetal /server:myserver /database:northwind /namespace:nwind /code:nwind.cs /language:csharp

To create an XML file from a database like Northwind, I copied the .mdf as suggested by the above help and pasted it to the same folder. I used the following command:
sqlmetal /xml:northwind.xml Northwind.mdf
but it failed with:

Unhandled Exception: System.Data.SqlClient.SqlException: An error has occurred while establishing a
connection to the server.  When connecting to SQL Server 2005, this failure may be caused by the fac
t that under the default settings SQL Server does not allow remote connections. (provider: SQL Netwo
rk Interfaces, error: 26 - Error Locating Server/Instance Specified)
   at System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConne
ction)

I thought its asking for the server name, so I tried this:
sqlmetal /xml:northwind.xml /server:myserver Northwind.mdf
it also failed with the following error:

Unhandled Exception: System.Data.SqlClient.SqlException: An attempt to attach an auto-named database
 for file Northwind.mdf failed. A database with the same name exists, or specified file cannot be op
ened, or it is located on UNC share.
   at System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConne
ction)

The command that worked is following:
sqlmetal /server:myserver /database:Northwind /xml:northwind.xml

Then I thought of creating a class out of the generated XML. I used the following command and it worked the first time:
sqlmetal /code:Northwind.cs /language:csharp Northwind.xml

Creating a class file directly from the database is pretty starightforward, I used the following command:
sqlmetal /server:myserver /database:Northwind /code:Northwind.cs /language:csharp

C# IDE Support for Visual Studio 2005/C# 2005 Express

While this preliminary IDE support greatly enhances the editing experience when writing C# 3.0 code in VS 2005, the language service and compiler are still very much in an alpha phase. In the event of a compiler error, many more errors may be reported than are actually present. If you see a large number of errors when building C# 3.0 code, fix the top error in the error list first and build after each fix.

Follow these steps to enable LINQ IDE support for Visual Studio 2005 and Visual C# 2005 Express:

First, verify that you are running the release version of Visual Studio 2005 or Visual C# 2005 Express. The language service that will be installed only works with the English version of VS 2005/C# 2005 Express and may cause severe problems if installed on earlier versions. You can verify your version by selecting Help\About in Visual Studio 2005.
Shut down any running instances of Visual Studio.
Open the \bin folder under the LINQ preview installation directory and run “Install C# IDE Support”.
Start VS 2005/C# 2005 Express.

Follow these steps to restore your original VS 2005/C# 2005 Express language service:

Shut down any running instances of Visual Studio.
Open the \bin folder under the LINQ preview installation directory and run “Uninstall C# IDE Support”.
Start VS 2005/C# 2005 Express.

How To: Seemlessly Export Data From Database to XML using LINQ

Sanjeet — Wed, 06 Jun 2007 14:47:24 GMT

While exploring a number of neat features available in the Visual C# Orcas Express Edition, you will see the following:

There is no namespace like DLinq, or XLinq anymore, they are replace with more meaningful
System.Data.Linq and
System.Xml.Linq

However, the latter appears by default in a console application, System.Data.Linq will be added to the references once the O/R mapper a.k.a .dbml file is added. In the express Edition, you can connect to a .mdf, .mdb, or a .sdf(Sql Server Compact Edition) databases.

After instantiating the DataContext class, you will be able to explore its rich features supported with Intellisence.

Apart from that the XML.Linq namespace has got some neat and intuitive features. My favorite is:
System.Xml.Linq.XElement xlinq = new XElement(XName name, object content);

As you would expect from it, any object returning values compatible to IEnumerable is taken care of by the constructor... all by itself.

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Xml.Linq;

namespace ConsoleApplication1

    class Program

        static void Main(string[] args)

            NorthwindDataContext north = new NorthwindDataContext();

            //sample query, not related to this demo!!

            var products = from p in north.Products

                           where p.ProductID > 10 && p.ProductID < 200

                           select new{

                                      p.ProductName,

                                      p.UnitPrice

};

            //the actual thing!!!

            System.Xml.Linq.XElement xlinq = new XElement("Products",

                                             from p in north.Products

                                             where p.ProductName.StartsWith("S")

                                             select new XElement("Product", new XAttribute("UnitPrice", p.UnitPrice),

                                                    new XAttribute("QuantityPerUnit", p.QuantityPerUnit),

                                                        new XElement("ProductName", p.ProductName),

                                                    new XElement("SupplierName", p.Supplier.CompanyName)

);

            xlinq.Save("NewXML.xml");

            Console.Write(xlinq);

            Console.Read();

The output in the (command window) looks like the following:

Check out this space, lots more coming up...

Microsoft ROCKS!!!

LINQ Lists - Anonymous Methods and Lambda Expressions

Sanjeet — Wed, 06 Jun 2007 14:22:36 GMT

Year: 2005 A.D.
The C# 2.0 specification is released in the month of September. It talks about "new" features. We were introduced with a new "in-line" feature of using delegates. We called it "Anonymous Methods". Needless to say, its named as such because:
- Its Anonymous (no method name is given)
- Its InLine (How can you call something without a name, makes sense doesn't it?)

Year: 2006 A.D.
The C# 3.0 specification is released in the month of May. It talks about new features. Among a number of path breaking innovative ideas, we have something called "Lambda Expressions". It claims to provide more concise, functional syntax for writing anonymous methods.

Lets checkout the basic syntax of Anonymous Methods:

delegate void D(int x);

D d1 = delegate { }; // Ok

D d2 = delegate() { }; // Error, signature mismatch

D d3 = delegate(long x) { }; // Error, signature mismatch

D d4 = delegate(int x) { }; // Ok

D d5 = delegate(int x) { return; }; // Ok

D d6 = delegate(int x) { return x; }; // Error, return type mismatch

delegate void E(out int x);

E e1 = delegate { }; // Error, E has an out parameter

E e2 = delegate(out int x) { x = 1; }; // Ok

E e3 = delegate(ref int x) { x = 1; }; // Error, signature mismatch

delegate int P(params int[] a);

P p1 = delegate { }; // Error, end of block reachable

P p2 = delegate { return; }; // Error, return type mismatch

P p3 = delegate { return 1; }; // Ok

P p4 = delegate { return "Hello"; }; // Error, return type mismatch

P p5 = delegate(int[] a) { // Ok

return a[0]; };

P p6 = delegate(params int[] a) { // Error, params modifier

return a[0]; };

P p7 = delegate(int[] a) { // Error, return type mismatch

if (a.Length > 0)

return a[0];

return "Hello";

};

delegate object Q(params int[] a);

Q q1 = delegate(int[] a) { // Ok

if (a.Length > 0)

return a[0];

return "Hello";

};

The best example of an anonymous method is when a delegate is used as an Event Handler:

Without Anonymous:

MyButton.Click += new EventHandler(MyButtonClicked);

void MyButtonClicked(object sender, EventArgs e)

MessageBox.Show("Hello World!");

With Anonymous:

MyButton.Click += delegate{

MessageBox.Show("Hello World!");

From the above comparison, you can make out that using InLine Functions, we do not need to:
- pass arguments across functions.
- you can use the scope level variables easily.
But, it has tradeoffs which involve code readability and reusability hassles. As the age old saying goes about InLine Functions: Use it efficiently, as its faster than calling functions but slightly difficult to manage.

Lambda Expressions

It is written as a parameter list, followed by the => (slanted lambda?) token, followed by an expression or a statement block.

class Program

    static void Main(string[] args)

        List<Vehicle> vlist = new List<Vehicle>

                                  new Vehicle{Make="Mercedes", Model="Benz", Mileage=12},

                                  new Vehicle{Make="Renault", Model="Logan", Mileage=15},

                                  new Vehicle{Make="Honda", Model="Accord", Mileage=12},

};

        IEnumerable<Vehicle> vehicles = vlist.Where(v => v.Mileage > 10);

        foreach (Vehicle v in vehicles)

            Console.WriteLine(v.Make);

            Console.WriteLine(v.Model);

            Console.WriteLine(v.Mileage);

            Console.WriteLine("-----------------");

        Console.Read();

public class Vehicle

    public string Make;

    public string Model;

    public int Mileage;

In the above example:
IEnumerable<Vehicle> vehicles = vlist.Where(v => v.Mileage > 10);

The Lambda Expression:
v => v.Mileage > 10

replaces:
new delegate(Vehicle v){
v.Mileage > 10;
}

It can also be replaced by:

IEnumerable<Vehicle> vehicles = from v in vlist

                                            where v.Mileage > 12

                                            select v;

Try this: The Evolution Of LINQ And Its Impact On The Design Of C#

These samples were created using: Microsoft Visual C# Codename "Orcas" Express Edition

The Var Of The Worlds

Sanjeet — Wed, 06 Jun 2007 08:30:23 GMT

Hello folks,

This time we will explore LINQ over a series of Posts.

As you must be knowing the age old "var" is back. But, is it the same old var that used to be in VB 6.0 days?

Precisely its not the same it has got a number of new features:
- You have to declare and instantiate it at the same line of code. Reason: It is smart enough to understand the assigned data type, and it becomes it.

var s = int.MaxValue; // it becomes Int32
var s2 = double.MaxValue; // it becomes double
var s3 = "The Var Of The Worlds" // string

- You cannot assign multiple data types to it. Any attempt to do so results in a compile time error.

Code with var:

   1: class Program

   2: {

   3:     static void Main(string[] args)

   4:     {

   5:         var s = from m in typeof(string).GetMethods()

   6:                 select m.Name;

   7:         foreach(string str in s)

   8:         {

   9:             Console.WriteLine(str);

  10:         }

  11:         Console.Read();

  12:     }

  13: }

Code without a var:

   1: class Program

   2: {

   3:     static void Main(string[] args)

   4:     {

   5:         IEnumerable<string> s  =

   6:             from m in typeof(string).GetMethods()

   7:             select m.Name;

8:

   9:         foreach(string str in s)

  10:         {

  11:             Console.WriteLine(str);

  12:         }

  13:         Console.Read();

  14:     }

  15: }