Explain DataView .

It provides a means to filter and sort data within a data table.
Example:
DataView myDataView = new DataView(myDataSet.Tables["Customers"]);

// Sort the view based on the FirstName column
myDataView.Sort = "CustomerID";

// Filter the dataview to only show customers with the CustomerID of ALFKI
myDataView.RowFilter = "CustomerID='ALFKI'";

Explain DataAdapter Object

It populates dataset from data source. It contains a reference to the connection object and opens and closes the connection automatically when reading from or writing to the database.

Example:
SqlDataAdapter daEmp = new SqlDataAdapter( "select EmpID, EmpName, Salary from Employees", conn);

Fill Method
It is used to populate dataset.
example: daEmp.Fill(dsEmp,"Employee");

Update Method
It is used to update database.
example: daEmp.Update(dsEmp,"Employee");

Explain DataSet Object .

Dataset is a disconnected, in-memory representation of data. It can contain multiple data table from different database.

They contain multiple Datatable objects, which contain columns and rows, just like normal data base tables. You can even define relations between tables to create parent-child relationships.

Example
DataSet dsEmp = new DataSet();

For more understanding look for DataAdapter Object.

Explain DataReader Object ?

It provides a forward-only, read-only, connected recordset.

It is most efficient to use when data need not to be updated, and requires forward only traverse. In other words, it is the fastest method to read data.

Example:

1. Filling dropdownlistbox.
2. Comparing username and password in database.

SqlDataReader rdr = cmd.ExecuteReader();
//Reading data
while (rdr.Read())
{
//Display data
string contact = (string)rdr["ContactName"];
string company = (string)rdr["CompanyName"];
string city = (string)rdr["City"];
}

What is Command Object ?

It allows to manipulate database by executing stored procedure or sql statements.

A SqlCommand object allows you to specify what type of interaction you want to perform with a data base.

For example, you can do select, insert, modify, and delete commands on rows of data in a data base table.
SqlCommand cmd = new SqlCommand("select * from Employees", conn);

What is Connection Object ?

It establishes connection.
The connection helps identify the data base server, the data base name, user name, password, and other parameters that are required for connecting to the data base.

Example:
SqlConnection conn = new SqlConnection( "Data Source=(local);Initial Catalog=Northwind;Integrated Security=SSPI");

What is Data Provider ?

A set of libraries that is used to communicate with data source. Eg: SQL data provider for SQL, Oracle data provider for Oracle, OLE DB data provider for access, excel or mysql.

What is Data Source ?

It can be a database, text file, excel spread sheet or an XML file.

What is ADO.net

ADO.net is data access architecture for the Microsoft .NET Framework.
ADO.NET is an object-oriented set of libraries that allows you to interact with data sources. Commonly, the data source is a data base, but it could also be a text file, an Excel spread sheet, or an XML file.

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What is difference between ExecuteReader, ExecuteNonQuery and ExecuteScalar.

What is difference between ExecuteReader, ExecuteNonQuery and ExecuteScalar.

ExecuteReader : Use for accessing data. It provides a forward-only, read-only, connected recordset.
ExecuteNonQuery : Use for data manipulation, such as Insert, Update, Delete.
ExecuteScalar : Use for retriving 1 row 1 col. value., i.e. Single value. eg: for retriving aggregate function. It is faster than other ways of retriving a single value from DB.

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SQL Injection

What is the sql injection 

SQL injection is a strategy for attacking databases.

1 : An ASP page asks the user for a name and a password, and then sends the following string to the database:
SELECT FROM users WHERE username = 'sqlinjection' AND password = 'mypass'

It seems safe, but it isn't. A user might enter something like this as her user name:
' OR 1>0 --

When this is plugged into the SQL statement, the result looks like this:
SELECT FROM users WHERE username = '' OR 1>0 -- AND password = ''

This injection comments out the password portion of the statement. It results in a list of all the names in the users table, so any user could get into your system.

The easiest way to prevent this sort of injection is to parse the SQL string and remove any occurrences of "--" before passing the statement.

Example 2:
You also have to beware of injections that contain semicolons because semicolons delimit SQL statements. Think about the implications of a user name like this:
' OR 1>0 ; DELETE Customers ; --

There are numerous ways a malicious user might penetrate your system using SQL injection and various defenses, but the simplest approach is to avoid dynamic SQL. Instead, use stored procedures everywhere. Thanks to the way SQL passes parameters, injections such as those above will produce errors, and the stored procedure will not execute.

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