The document discusses connected and disconnected environments in ADO.NET. A connected environment maintains a constant connection to the data source, while a disconnected environment does not directly connect. It also covers synchronous and asynchronous operations using command objects, and how asynchronous commands can improve performance by executing in parallel. Methods like BeginExecuteReader() and EndExecuteReader() are used for asynchronous retrieval and completion of data.

1. Developing Database Applications Using ADO.NET and XML
Objectives
In this session, you will learn to:
Identify the connected and disconnected environment in
ADO.NET
Working in a connected environment
Ver. 1.0 Session 4 Slide 1 of 14

2. Developing Database Applications Using ADO.NET and XML
Introducing Connected and Disconnected Environment
A connected environment is one in which a user or an
application is constantly connected to a data source.
A connected environment provides the following
advantages:
Data concurrency issues are easier to control.
Data is current and updated.
A connected environment has the following disadvantages:
A constant network connection may, sometimes, lead to
network traffic logging.
Scalability and performance issues in applications.
Let us now discuss the disconnected environment.
Ver. 1.0 Session 4 Slide 2 of 14

3. Developing Database Applications Using ADO.NET and XML
Introducing Connected and Disconnected Environment (Contd.)
In a disconnected environment is one in which a user or an
application is not directly connected to a data source.
A disconnected environment provides the following
advantages:
Allows multiple applications to simultaneously interact with the
data source.
Improves the scalability and performance of applications.
A disconnected environment has the following
disadvantages:
Data is not always up to date as no proper connection is
established with the data source.
Data concurrency issues can occur when multiple users are
updating the data to the data source.
Ver. 1.0 Session 4 Slide 3 of 14

4. Developing Database Applications Using ADO.NET and XML
Introducing Connected and Disconnected Environment (Contd.)
The following figure shows the connected and disconnected
environment in ADO.NET.
XML Data Source
Ver. 1.0 Session 4 Slide 4 of 14

5. Developing Database Applications Using ADO.NET and XML
Working with Command Objects
A Command object is a specific command that is used to
manipulate data in a data source in a connected
environment.
A Command object represents a DML statement or a stored
procedure that is used to retrieve, insert, delete, or modify
data in a data source.
The two types of operations performed by a command
object to retrieve and modify data in a data source are:
Synchronous operations
Asynchronous operations
Let us discuss these operations in detail.
Ver. 1.0 Session 4 Slide 5 of 14

6. Developing Database Applications Using ADO.NET and XML
Working with Command Objects (Contd.)
During synchronous operations, the command objects are
linked to each other.
Executing command objects synchronously results in a
sequential execution, where each database command must
complete before the next command is executed.
Synchronous operations are performed with the help of the
following command objects:
 DbCommand object Executes a command in a data source
against a valid open connection
 DbParameters object Assigns parameterized values to stored
procedures
 DbDataReader object Retrieves a forward-only, read-only data
from the data source
Ver. 1.0 Session 4 Slide 6 of 14

7. Developing Database Applications Using ADO.NET and XML
Just a minute
• Which method of the DbCommand object executes a DML
statement against a connection and returns the number of
rows affected?
1. ExecuteReader()
2. CreateObjRef()
3. ExecureNonQuery()
4. ExecuteScalar()
Answer:
3. ExecuteNonQuery()
Ver. 1.0 Session 4 Slide 7 of 14

8. Developing Database Applications Using ADO.NET and XML
Working with Command Objects (Contd.)
• Asynchronous execution of commands enhances the
overall performance and responsiveness of the client
application.
• ADO.NET supports asynchronous execution of commands
to enable parallelism by allowing the client application to
execute commands while waiting for the response from a
previously issued command.
• The asynchronous execution of commands is carried out in
the SQLCommand class.
Ver. 1.0 Session 4 Slide 8 of 14

9. Developing Database Applications Using ADO.NET and XML
Working with Command Objects (Contd.)
• The SQLCommand class provides the following methods for
asynchronous execution of commands:
 BeginExecuteNonQuery() Starts the process of asynchronously
executing a Transact-SQL statement or
stored procedure that does not return
rows
 BeginExecuteReader() Starts the process of asynchronously
executing a Transact-SQL statement or
stored procedure that returns rows
 BeginExecuteXmlReader() Initiates the asynchronous execution of
the Transact-SQL statement or stored
procedure that is described by the
SqlCommand and returns the result as
an XMLReader object
Ver. 1.0 Session 4 Slide 9 of 14

10. Developing Database Applications Using ADO.NET and XML
Working with Command Objects (Contd.)
 EndExecuteNonQuery() Completes the asynchronous execution
of a Transact-SQL statement or stored
procedure
 EndExecuteReader() Completes the asynchronous execution
of a Transact-SQL statement or a stored
procedure, thereby, returning the
requested SqlDataReader
 EndExecuteXmlReader() Completes the asynchronous execution
of a Transact-SQL statement or a stored
procedure, thereby, returning XML data
Ver. 1.0 Session 4 Slide 10 of 14

11. Developing Database Applications Using ADO.NET and XML
Working with Command Objects (Contd.)
Another way of retrieving data asynchronously is by using
Multiple Active Result Sets (MARS).
MARS allows the execution of multiple data readers on a
single connection.
By default, MARS feature is disabled in an application. You
can enable MARS in the connection string, as shown in the
following code snippet:
String connectionString = "Data
Source=SQLSERVER01;Initial
Catalog=AdventureWorks;User
id=sa;Password=niit#1234;
MultipleActiveResultSets=True"; Enabling MARS property
to True
Ver. 1.0 Session 4 Slide 11 of 14

12. Developing Database Applications Using ADO.NET and XML
Just a minute
• What is the function of the EndExecuteReader()
method of the SqlCommand class?
1. Asynchronously executes a stored procedure that returns
rows
2. Executes the stored procedure and returns the result as an
XmlReader object
3. Asynchronously executes a stored procedure that does not
return rows
4. Executes the stored procedure and returns the result as an
SqlDataReader object
Answer:
4. Executes the stored procedure and returns the result as an
SqlDataReader object
Ver. 1.0 Session 4 Slide 12 of 14

13. Developing Database Applications Using ADO.NET and XML
Summary
In this session, you learned that:
A connected environment is one in which a user or an
application is constantly connected to a data source.
A disconnected environment is one in which a user or an
application is not directly connected to a data source.
The two types of operations performed by a command object
to retrieve and modify data in a data source are:
 Synchronous operations
 Asynchronous operations
 During synchronous operations, the command objects are
linked to each other.
 Synchronous operations are performed with the help of the
following command objects:
 DbCommand object
 DbParameters object
 DbDataReader object
Ver. 1.0 Session 4 Slide 13 of 14

14. Developing Database Applications Using ADO.NET and XML
Summary (Contd.)
 ADO.NET supports asynchronous execution of commands to
enable parallelism by allowing the client application to execute
commands while waiting for the response from a previously
issued command.
 The SqlCommand class provides the following methods for
asynchronous operations:
 BeginExecuteNonQuery()
 BeginExecuteReader()
 BeginExecuteXmlReader()
 EndExecuteNonQuery()
 EndExecuteReader()
 EndExecuteXmlReader()
 MARS allows the execution of multiple data readers on a single
connection.
Ver. 1.0 Session 4 Slide 14 of 14