Ado.net session08

Developing Database Applications Using ADO.NET and XML
Objectives

In this session, you will learn to:
Retrieve and store large binary data
Perform bulk copy operations
Enable SQL notification to maintain and update a cache

Ver. 1.0 Session 8 Slide 1 of 28

Handling Binary Large Objects in a Database

While working with data, you may need to move large
objects (LOB) between the client application and the
database server.
LOBs are of different formats:
 Binary Large Object (BLOB): If a LOB is stored in a database
in a binary format, it is referred to as BLOB.
 Character Large Object (CLOB): If a LOB is stored in the
database in a textual format, it is referred to as CLOB.


Retrieving BLOB Data

• To access the DataReader object in a stream fashion, you
can change the DbCommand object’s behavior to a
sequential stream when you execute the
ExecuteReader() method.
• In the stream mode, you must get the bytes from the stream
in the order of each column that is being returned.
• Refer to following code snippet that retrieves photographs
and stores them into a file:
byte[] outbyte = new Declare the BLOB byte[]
byte[bufferSize]; buffer, which will be filled by
GetBytes. bufferSize
connection.Open(); Open the connection and read
refers to the size of the BLOB
SqlDataReader myReader = buffer. the DataReader.
data into
command.ExecuteReader
(CommandBehavior.
SequentialAccess);
while (myReader.Read()){

Retrieving BLOB Data (Contd.)

string fileName = Create a file to store the image.
@"C:Patient" + ".bmp";
fs = new Write the BLOB to a .bmp file.
FileStream(fileName,
FileMode.OpenOrCreate,
FileAccess.Write);
bw = new BinaryWriter(fs); Stream the BLOB to the
FileStream object, fs.
startIndex = 0; Reset the starting position.
bw is an object of
retval = Read the bytes into outbyte[]
BinaryWriter.
myReader.GetBytes(1, and store the number of bytes
returned.
startIndex, outbyte, 0,
bufferSize);
while (retval == bufferSize) Continue to read and write while
{ bytes are remaining.
bw.Write(outbyte);
bw.Flush();


Retrieving BLOB Data (Contd.)

startIndex += Reposition the start index to the
end of the last buffer and fill the
bufferSize; retval = buffer.
myReader.GetBytes(1,
startIndex, outbyte,
0, bufferSize);
}
bw.Write(outbyte, 0, Write the remaining buffer.
(int)retval - 1);
bw.flush();


Storing BLOB Data

• You can write BLOB data to a database by executing
INSERT or UPDATE statement.
• If the BLOB data is stored in a text format, you can pass the
data as a string parameter.
• The following code snippet updates a photograph with a
new one from the file:
command.CommandText = "Select Retrieve a pointer to the
photograph.
TEXTPTR(PatientPhoto)
The SQL Server TEXTPTR
from Patients where function is first called to get a
PatientId='1004'"; pointer to the field of the record
photoPtr = to be updated.
(byte[])command.ExecuteScalar();


Storing BLOB Data (Contd.)

using (SqlCommand command =
connection.CreateCommand())
command.CommandText =
"UPDATETEXT The SQL Server UPDATETEXT
function writes the BLOB data in
Patients.PatientPhoto chunks of a specified size.
@Pointer @Offset null The pointer entire existing the photograph.
Delete the to the start of data.
current offset to insert data.
@Data"; SqlParameter ptrParm The data being sent to the database.
= command.Parameters.Add
("@Pointer",
SqlDbType.Binary, 16);
ptrParm.Value = photoPtr;
SqlParameter photoParm =
command.Parameters.Add("@Dat
a", SqlDbType.Image);
SqlParameter offsetParm =
command.Parameters.Add("@Off
set", SqlDbType.Int);


Storing BLOB Data (Contd.)

offsetParm.Value = 0;
using (FileStream file = new Read chunks of the file into
FileStream("C:newPhoto.gif“, the buffer and send the
chunks to the database.
FileMode.Open,
FileAccess.Read)){
int count = file.Read (buffer,
0, bufferSize);
while (count != 0)
{ photoParm.Value = buffer;
photoParm.Size = count;
command.ExecuteNonQuery();
currentIndex += count;
offsetParm.Value =
currentIndex;
count = file.Read(buffer, 0,
bufferSize);}}


Just a minute

Fill in the blanks:
The SQL Server _______ function is first called to get a
pointer to the field of the record to be updated.

Answer:
TEXTPTR


Just a minute

Fill in the blanks:
The SQL Server _______ function writes the BLOB data in
chunks of a specified size.

Answer:
UPDATETEXT


Demo: Handling BLOB Data From a Database

Problem Statement:
A new employee has joined Tebisco. The details of this
employee need to be inserted to the Employees table. The
details are as follows:
 Employee code: 000017
 First name: Peter
 Last name: Martin
In addition, the photograph of the employee should be
uploaded to the database. It should be displayed after the
photograph is inserted. Create an application that will perform
the required tasks.


Performing Bulk Copy Operations

• There can be occasions when you need to copy large
amounts of data from one location to another.
• The SqlBulkCopy class allows you to write bulk in SQL
Server based tables.
• The data is copied from the data source to the destination
table, specified by the DestinationTableName property,
by using the WritetoServer() method of the
SqlBulkCopy class.


Performing Bulk Copy Operations (Contd.)

• The following figure displays the various parameters that
can be passed to the WritetoServer() method in order
to copy data in bulk.
WritetoServer()
Data DataRow Array SQL
Source DataTable Server
IDataReader
DataRowState

Copies all rows from the DataRow array to a destination table

Copies all rows in the DataTable to a destination table

Copies all rows in the IDataReader interface to a destination table

Copies only rows that match the row state in the DataTable to a
destination


Executing Single Bulk Copy Operations

A single bulk copy command is executed to perform a single
operation against a database.
To perform the bulk copy operation, you need to perform the
following steps:
• Connect to the source server using (SqlConnection
sourceConnection = new
to get the data to be copied.
SqlConnection(connectionString)){
• Connect to the destination sourceConnection.Open();
server. SqlCommand commandSourceData = new
SqlCommand("SELECT * FROM
• Create a SqlBulkCopy sourceTable;", sourceConnection);
object. SqlDataReader reader =
commandSourceData.ExecuteReader();
• Set the
DestinationTableName
property to the name of the
target table.
• Call the WriteToServer()
method.

Executing Single Bulk Copy Operations (Contd.)

following steps:
• Connect to the source server
• Connect to the destination using (SqlConnection
server. destinationConnection = new
SqlConnection(connectionString))
• Create a SqlBulkCopy { destin
object. ationConnection.Open();
}
• Set the
target table.
method.


following steps:
• Connect to the destination
server.
• Create a SqlBulkCopy using (SqlBulkCopy bulkCopy =
new SqlBulkCopy
object. (destinationConnection))
• Set the
target table.
method.


following steps:
server.
• Create a SqlBulkCopy
object.
• Set the bulkCopy.DestinationTableName =
DestinationTableName "targetTable";
target table.
method.


following steps:
server.
• Create a SqlBulkCopy
object.
• Set the
target table.
• Call the WriteToServer() bulkCopy.WriteToServer(reader);
method.

Just a minute

Which class is used for bulk copy of records?

Answer:
SqlBulkCopy


Executing Multiple Bulk Copy Operations

• Multiple bulk copy command is executed to perform multiple
operations against a database.
• It can be done by using a single instance of
a SqlBulkCopy class.
• Performing multiple bulk copy operations by using the same
instance of SqlBulkCopy is usually more efficient than by
using a separate instance for each operation.


Demo: Performing Bulk Copy Operations

Problem Statement:
The employee details of Tebisco are stored in the Employees
table of the HR database. The records of this table have got
deleted accidentally. However, a backup copy of the table is
available. This table is of the name EmployeeBackUp. The
records from the EmployeeBackUp table need to be copied to
the Employees table.
You are a developer in Tebisco. You have been told to create
an application that will copy the records from EmployeeBackUp
to Employees table. Create an application that will perform the
required task in the shortest possible time.


SQL Notification

Data caching improves the performance of applications
because it prevents repeated roundtrips to the database
server. In this way, database resources are conserved.
However, ensuring that the cache maintains updated
records is a challenging task. You need to know when the
cache expires, that is, when the data has been modified in
the database server.
To provide this functionality, SQL notification, which is
based on the Service Broker infrastructure, is used.


Enabling SQL Notification

To use query notifications, you need to:
• Enable Service Broker for ALTER DATABASE DATABASE_NAME
SET ENABLE_BROKER;
the database.
CREATE QUEUE
ContactChangeMessages;
• Ensure that the user ID CREATE SERVICE
USE DATABASE_NAME
ContactChangeNotifications
used to connect to the GRANT SUBSCRIBE QUERY
ON QUEUE
database has the necessary NOTIFICATIONS TO
ContactChangeMessages
database_principal
permissions. ([http://schemas.microsoft
.com/SQL/Notifications/Pos
SqlClientPermission permission
tQueryNotification]);
= new
SqlClientPermission(Permission
State.Unrestricted);
try{
permission.Demand();
return true;
}


Executing SQL Notification

To execute SQL notification, you need to:
 Initialize the SqlDependency.Start(connectio
SqlDependency class nString);
using the Start()
method. This method
takes a connection string
as a parameter.
 Set the Notification using (SqlCommand cmd = new
property of the SqlCommand(sql, cn))
SqlCommand object. It is {
set by passing an object cn.Open();
of SqlCommand to the dep = new
constructor of SqlDependency(cmd);
SqlDependency object.
 Declare the OnChange dep.OnChange += dep_OnChange;
event on the
SqlDependency object.

Just a minute

How would you enable Service Broker for a database called
Northwind?

Answer:
ALTER DATABASE Northwind SET ENABLE_BROKER;


Demo: Implementing SQL Notification

Problem Statement:
The details of the various positions in Tebisco are stored in a
Position table, which is maintained by the HR management
team. This table has the following fields:
 Position code
 Description
 Budgeted strength
 Year
 Current strength
The budgeted strength and the current strength fields of this
table are frequently modified. As a result, the management of
Tebisco has decided to cache the records of this table. Create
an application that will notify the vacancy initiation application
about any change in values of these two fields for the current
year.


Summary

In this session, you learned that:
 While working with large objects (LOB), it is advisable to use
streaming techniques. This conserves the system resources.
 If a LOB is stored in the database in a binary format, it is
referred to as Binary Large Object (BLOB).
 The normal operation of the DataReader object is to read one
row at a time. To access the DataReader object in a stream
fashion, you can change the DbCommand object’s behavior to a
sequential stream when you execute the ExecuteReader()
method.
 You can use the SQL Server UPDATETEXT function to write the
BLOB data in chunks of a specified size. The UPDATETEXT
function requires a pointer to the BLOB field being updated, so
the SQL Server TEXTPTR function is first called to get a pointer
to the field of the record to be updated.


Summary (Contd.)

 The SqlBulkCopy class is used to copy large amounts of
data to the SQL Server database tables.
 A single bulk copy command is executed to perform a single
 Multiple bulk copy command is executed to perform multiple
operations against a database.
 Multiple bulk copy operation can be done by using a
single instance of a SqlBulkCopy class (for SQL Server).
 Query notifications are useful for applications that need to
refresh displays or caches.
To use query notifications, you need to:
 Enable query notifications for your database.
 Ensure that the user ID used to connect to the database has the
necessary permissions.
 To execute SQL notifications, you need to use the
SqlDependency class.


Ado.net session08

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