DataContract vs Serializable WCF

When applied to a class Serializable attribute serializes everything inside of it including private fields thus the developer has no control as what to expose.

When DataContract attribute is applied to a class it will serialize only the elements decorated with DataMember attribute thus the developer will have more control.

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ServiceContract Name property WCF

This property can give your contract a name which is different from the actual interface name. So this way if you decide to change the interface name of a already running WCF service your client wont break.

Ex:

 [ServiceContract(Name="IGoodbyeService")]

    public interface IHelloService

    {

        [OperationContract]

        string GetMessage(string name);

    }

Now the contract name would be IGoodbyeService rather than  IHelloService.

To verify in the WSDL generated check the porttype property it should be IGoodbyeService

Note: Same can be done for OperationContract as well 

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Basic Elements of WCF Appconfig

All config items should be inside ,

<system.serviceModel>

This is the WCF namespace provided by Microsoft.

Inside the <system.serviceModel> element you have the <services> element. This is where you configure all your services.
For each service you have a <service> element inside <services> element.
A particular service can be exposed using more than one endpoint. (Ex: http , net.tcp etc)
So for each endpoint in a service you configure a <endpoint> element.
An endpoint element will have three essential things,

1. address
2. binding
3. contract  

Here is a  sample config (not complete) to get an idea.

The service name is HelloService (class and namespace both are HelloService) and has two endpoints (http and net.tcp) for the service.

<?xml version="1.0" encoding="utf-8" ?>


<configuration>

  <system.serviceModel>

    <services>

      <service name="HelloService.HelloService">

        <endpoint address="HelloService" binding="basicHttpBinding" contract="HelloService.IHelloService">

        </endpoint>

        <endpoint address="HelloService" binding="netTcpBinding" contract="HelloService.IHelloService">

        </endpoint>

      </service>

    </services>

  </system.serviceModel>

</configuration>

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system.web vs system.webserver

I have not worked in IIS6 and mostly I have worked on IIS 7+ and this came up when I was following a very old article (2003) ASP.Net article.

Anyway system.web is IIS6 and classic mode.
system.webserver is IIS7+  and integrated mode.

One scenario you might come across is when adding httpmodules to your ASP.Net project. If you want backward compatibility then you should add the module section to both system.web section (which is there by default for all ASP.Net projects ) and to system.webserver.

<system.web>
    <httpModules>
    </httpModules>
</system.web>

And

<system.webServer>
    <modules>
    </modules>
</system.webServer>

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SQL JOIN Example

Joins can be quite perplexing initially hopefully this simple example will help. 

Joins are used to combine data from multiple tables (usually two tables)

There are three types of joins,

1. INNER

2. OUTER - FULL, LEFT, RIGHT

3. CROSS

For all examples I'll be using the below given tables and use the Name field as the condition.

                                                                         Table1

Id1	Name1
1	Padmika
2	Dissanayake
3	Sukitha
4	Pahan

                                                                        Table2

Id2	Name2
1	Fernando
2	Malaka
3	Padmika
4	Sukitha

1. INNER JOIN

Returns only the set of records that match the Name field in both Table 1 and Table2

SELECT * FROM Table1

INNER JOIN Table2

ON Table1.Name1 = Table2.Name2

Result,

Id1	Name1	Id2	Name2
1	Padmika	3	Padmika
3	Sukitha	4	Sukitha

* This gets executed in the following manner, first get the first record from Table 1 get its name field compare it to Table 2 first record name field if it’s a match return it, now compare with Table2 second record name field…  etc.

You will see that only the records that have a common name is returned

This is similar to the intersection of two sets (Table1 and Table2) based on Name.  

2. OUTER JOIN

2.1 FULL OUTER JOIN

Returns all records in Table 1 and Table 2, with matching records from both sides where available. If there is no match, the missing side will contain null.

SELECT * FROM Table1

FULL OUTER JOIN Table2

ON Table1.Name1 = Table2.Name2

Result,

Id1	Name1	Id2	Name2
1	Padmika	3	Padmika
2	Dissanayake	null	Null
3	Sukitha	4	Sukitha
4	Pahan	null	Null
null	Null	1	Fernando
null	Null	2	Malaka

This is similar to the union of two sets (Table1 and Table2) based on Name.

2.2 LEFT OUTER JOIN

 Returns the complete set of records from Table 1 (Left table), with the matching records for Name field (where available) in Table 2. If there is no match, the right side will contain null.

SELECT * FROM Table1

LEFT OUTER JOIN Table2

ON Table1.Name1 = Table2.Name2

Results,

Id1	Name1	Id2	Name2
1	Padmika	3	Padmika
2	Dissanayake	null	null
3	Sukitha	4	Sukitha
4	Pahan	null	null

Special case of the above result would be to select records that do not have any matching records from the right table (Table2)

To do this just add a ‘WHERE Table2.Id2 IS NULL’ clause to the above query.

Ex: You have a Customer table and an Order table (Has a CustomerID column) and want to find out which customers have not placed any orders  

2.3 RIGHT OUTER JOIN

Similar to the above but all the right table (Table2) records will return rather than the left table ones.

SELECT * FROM Table1

RIGHT OUTER JOIN Table2

ON Table1.Name1 = Table2.Name2

Results,

Id1	Name1	Id2	Name2
null	null	1	Fernando
null	null	2	Malaka
1	Padmika	3	Padmika
3	Sukitha	4	Sukitha

Note : When inspected carefully you will see that in this example,

OUTER JOIN result = LEFT JOIN result + RIGHT JOIN result – INNER JOIN result

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SQL COUNT Example

COUNT returns the number of rows in a select statement (Also note that it doesn't consider null values),

Note : I'll be using the AdventureWorks2008R2 sample database which can be downloaded from here,

http://msftdbprodsamples.codeplex.com/releases/view/59211


Example 1,

/* By using the * we return the number of records in the Sales.Customer table */

select

count(*)

from Sales.Customer;

Example 2,

/* By using StoreID inside the COUNT() function we return the number of store id's in the Sales.Customer table */

select

count(StoreID)

from Sales.Customer;

Example 3,
  /* By using "DISTINCT StoreID" inside the COUNT() function we return the unique number of store id's in the Sales.Customer table */

select

count(distinct StoreID)

from Sales.Customer;

Note: From a performance point of view it is better to use 1 instead of * inside the COUNT function.

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DDL vs DML in SQL Server

DDL
Data Definition Language (DDL) statements are used to define the database structure or schema. Examples:

• CREATE - to create objects in the database
• ALTER - alters the structure of the database
• DROP - delete objects from the database

DML
Data Manipulation Language (DML) statements are used for managing data within schema objects. Examples:

• SELECT - retrieve data
• INSERT - add data
• UPDATE - modify data
• DELETE - remove data

Note : This is not limited to SQL Server

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