List Example with Keyvaluepair

KeyValuePair

var myList = new List<KeyValuePair<int, string>>();
myList.Add(new KeyValuePair<int, string>(1, "One");

foreach (var item in myList)
{
    int i = item.Key;
    string s = item.Value;
}
or if you are .NET Framework 4 you could use:

var myList = new List<Tuple<int, string>>();
myList.Add(Tuple.Create(1, "One"));

foreach (var item in myList)
{
    int i = item.Item1;
    string s = item.Item2;
}
If either the string or integer is going to be unique to the set, you could use:

Dictionary<int, string> or Dictionary<string, int>

Difference between a stack, a queue and a heap

A stack keeps track of what is executing and contains stored value types to be accessed and processed as Last In First Out, with elements both inserted and deleted from the top end.

A queue lists items on a First In First Out basis in terms of both insertion and deletion, with the developer inserting items from the rear end and deleting items from the front end of the queue.

A heap contains stored reference types and is responsible for keeping track of more precise objects.

Read-only variables VS Constants

1. Read-only variables can support reference-type variables. Constants can hold only value-type variables.

2. Developers evaluate read-only variables at the runtime. They evaluate constants at the compile time.

LINQ

LINQ stands for Language Integrated Query.

Language-Integrated Query (LINQ) is an innovation introduced in Visual Studio 2008 and .NET Framework version 3.5 that bridges the gap between the world of objects and the world of data.

You can use LINQ queries in new projects, or alongside non-LINQ queries in existing projects. The only requirement is that the project target .NET Framework 3.5 or later.

This is a Microsoft programming model and methodology that offers developers a way to manipulate data using a succinct yet expressive syntax. It does so by instilling Microsoft .NET-based programming languages with the ability to make formal queries

In Visual Studio you can write LINQ queries in Visual Basic or C# with SQL Server databases, XML documents, ADO.NET Datasets, and any collection of objects that supports IEnumerable or the generic IEnumerable<T> interface. LINQ support for the ADO.NET Entity Framework is also planned, and LINQ providers are being written by third parties for many Web services and other database implementations.

WCF

WCF stands for Windows Communication Foundation.It is a framework for building, configuring, and deploying network-distributed services

WCF was released for the first time in 2006 as a part of the .NET framework with Windows Vista, and then got updated several times. WCF 4.5 is the most recent version that is now widely used.

A WCF application consists of three components:

• WCF service,
• WCF service host, and
• WCF service client.

Fundamental Concepts of WCF

Message

This is a communication unit that comprises of several parts apart from the body. Message instances are sent as well as received for all types of communication between the client and the service.

Endpoint

It defines the address where a message is to be sent or received. It also specifies the communication mechanism to describe how the messages will be sent along with defining the set of messages. A structure of an endpoint comprises of the following parts:

• Address - Address specifies the exact location to receive the messages and is specified as a Uniform Resource Identifier (URI). It is expressed as scheme://domain[:port]/[path]. Take a look at the address mentioned below:
  net.tcp://localhost:9000/ServiceA
  Here, 'net.tcp' is the scheme for the TCP protocol. The domain is 'localhost' which can be the name of a machine or a web domain, and the path is 'ServiceA'.

• Binding - It defines the way an endpoint communicates. It comprises of some binding elements that make the infrastructure for communication. For example, a binding states the protocols used for transport like TCP, HTTP, etc., the format of message encoding, and the protocols related to security as well as reliability.
• Contracts - It is a collection of operations that specifies what functionality the endpoint exposes to the clinet. It generally consists of an interface name.

Hosting

Hosting from the viewpoint of WCF refers to the WCF service hosting which can be done through many available options like self-hosting, IIS hosting, and WAS hosting.

Metadata

This is a significant concept of WCF, as it facilitates easy interaction between a client application and a WCF service. Normally, metadata for a WCF service is generated automatically when enabled, and this is done by inspection of service and its endpoints.

WCF Client

A client application that gets created for exposing the service operations in the form of methods is known as a WCF client. This can be hosted by any application, even the one that does service hosting.

Channel

Channel is a medium through which a client communicates with a service. Different types of channels get stacked and are known as Channel Stacks.

SOAP

Although termed as ‘Simple Object Access Protocol’, SOAP is not a transport protocol; instead it is an XML document comprising of a header and body section.

Advantages of WCF

• It is interoperable with respect to other services. This is in sharp contrast to .NET Remoting in which both the client and the service must have .Net.
• WCF services offer enhanced reliability as well as security in comparison to ASMX (Active Server Methods) web services.
• Implementing the security model and binding change in WCF do not require a major change in coding. Just a few configuration changes is required to meet the constraints.
• WCF has built-in logging mechanism whereas in other technologies, it is essential to do the requisite coding.
• WCF has integrated AJAX and support for JSON (JavaScript object notation).
• It offers scalability and support for up-coming web service standards.
• It has a default security mechanism which is extremely robust.

difference between WCF and Web services

Features	Web Service	WCF
Hosting	It can be hosted in IIS	It can be hosted in IIS, windows activation service, Self-hosting, Windows service
Programming	[WebService] attribute has to be added to the class	[ServiceContraact] attribute has to be added to the class
Model	[WebMethod] attribute represents the method exposed to client	[OperationContract] attribute represents the method exposed to client
Operation	One-way, Request- Response are the different operations supported in web service	One-Way, Request-Response, Duplex are different type of operations supported in WCF
XML	System.Xml.serialization name space is used for serialization	System.Runtime.Serialization namespace is used for serialization
Encoding	XML 1.0, MTOM(Message Transmission Optimization Mechanism), DIME, Custom	XML 1.0, MTOM, Binary, Custom
Transports	Can be accessed through HTTP, TCP, Custom	Can be accessed through HTTP, TCP, Named pipes, MSMQ,P2P, Custom
Protocols	Security	Security, Reliable messaging, Transactions

SQL Server CROSS APPLY and OUTER APPLY

Creating some temporary objects

CREATE TABLE ##Department( 

   [DepartmentID] [int] NOT NULL PRIMARY KEY, 

   [Name] VARCHAR(250) NOT NULL, 

) ON [PRIMARY] 

INSERT ##Department ([DepartmentID], [Name])  

VALUES (1, N'Engineering') 

INSERT ##Department ([DepartmentID], [Name])  

VALUES (2, N'Administration') 

INSERT ##Department ([DepartmentID], [Name])  

VALUES (3, N'Sales') 

INSERT ##Department ([DepartmentID], [Name])  

VALUES (4, N'Marketing') 

INSERT ##Department ([DepartmentID], [Name])  

VALUES (5, N'Finance') 

GO 

CREATE TABLE ##Employee( 

   [EmployeeID] [int] NOT NULL PRIMARY KEY, 

   [FirstName] VARCHAR(250) NOT NULL, 

   [LastName] VARCHAR(250) NOT NULL, 

   [DepartmentID] [int] NOT NULL , 

) ON [PRIMARY] 

GO 

INSERT ##Employee ([EmployeeID], [FirstName], [LastName], [DepartmentID]) 

VALUES (1, N'Sendhil', N'Kumar', 1 ) 

INSERT ##Employee ([EmployeeID], [FirstName], [LastName], [DepartmentID]) 

VALUES (2, N'Arun', N'Kumar', 2 ) 

INSERT ##Employee ([EmployeeID], [FirstName], [LastName], [DepartmentID]) 

VALUES (3, N'Vivek', N'Ram', 3 ) 

INSERT ##Employee ([EmployeeID], [FirstName], [LastName], [DepartmentID]) 

VALUES (4, N'Bill', N'Gates', 3 )

CROSS APPLY and INNER JOIN

SELECT * FROM ##Department D 

CROSS APPLY 

   ( 

   SELECT * FROM ##Employee E 

   WHERE E.DepartmentID = D.DepartmentID 

   ) A 

GO 

SELECT * FROM ##Department D 

INNER JOIN ##Employee E ON D.DepartmentID = E.DepartmentID 

GO

OUTER APPLY and LEFT OUTER JOIN

SELECT * FROM ##Department D 

OUTER APPLY 

   ( 

   SELECT * FROM ##Employee E 

   WHERE E.DepartmentID = D.DepartmentID 

   ) A 

GO 

SELECT * FROM ##Department D 

LEFT OUTER JOIN ##Employee E ON D.DepartmentID = E.DepartmentID 

GO 

Difference between String and string in c#

There is no such difference between string and String (Syetem.String). The "string" keyword is an alias for System.String in the .NET Framework. So the String and string are equal and you can use whichever naming convention you prefer.