Ddcauado.net Session04

7/30/2019 Ddcauado.net Session04

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Developing Data-Centric Applications Using ADO.NET

Session 4

In this session, you will learn to:

Identify the connected and disconnected environment in

ADO.NET

Working in a connected environment

Objectives


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Session 4

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.

Introducing Connected and Disconnected Environment


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Session 4

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 thedata 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 isestablished with the data source.

Data concurrency issues can occur when multiple users are

updating the data to the data source.

Introducing Connected and Disconnected Environment (Contd.)


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Session 4

The following figure shows the connected and disconnected

environment in ADO.NET.

Introducing Connected and Disconnected Environment (Contd.)

XML Data Source


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Session 4

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 modifydata 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 operationsLet us discuss these operations in detail.

Working with Command Objects


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Session 4

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

DbParameters object

DbDataReader object

Working with Command Objects (Contd.)

Executes a command in a data source

against a valid open connection

Assigns parameterized values to storedprocedures

Retrieves a forward-only, read-only data

from the data source


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Session 4

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()

Just a minute

Answer:

3. ExecuteNonQuery()




Session 4

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 apreviously issued command.

The asynchronous execution of commands is carried out inthe SQLCommand class.





Session 4

The SQLCommand class provides the following methods for

asynchronous execution of commands:

BeginExecuteNonQuery()

BeginExecuteReader()

BeginExecuteXmlReader()


Starts the process of asynchronously

executing a Transact-SQL statement or

stored procedure that does not return

rows

Starts the process of asynchronously

executing a Transact-SQL statement or

stored procedure that returns rows

Initiates the asynchronous execution of

the Transact-SQL statement or stored

procedure that is described by theSqlCommand and returns the result as

an XMLReader object


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Session 4

EndExecuteNonQuery()

EndExecuteReader()

EndExecuteXmlReader()


Completes the asynchronous execution

of a Transact-SQL statement or stored

procedure


of a Transact-SQL statement or a stored

procedure, thereby, returning therequested SqlDataReader


of a Transact-SQL statement or a stored

procedure, thereby, returning XML data


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Session 4

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. Youcan 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


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Session 4

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 anXmlReader object

3. Asynchronously executes a stored procedure that does not

return rows

4. Executes the stored procedure and returns the result as anSqlDataReader object

Just a minute

Answer:

4. Executes the stored procedure and returns the result as anSqlDataReader object


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Session 4

A data adapter is integral to the working of ADO.NET

because data is transferred to and from a database through

a data adapter.

A data adapter retrieves data from a database into a

dataset.

The data adapter first compares the data in the dataset with

that in the database and then updates the database.

Data from a database can be accessed by configuring a

data adapter.

Working with Data Adapters


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Following are the data adapters that can be configured to

connect to a database:

SqlDataAdapter

OleDbDataAdapter

OdbcDataAdapter

OracleDataAdapter

Working with Data Adapters (Contd.)

Accesses data specifically from Microsoft

SQL Server

Accesses data from a database that is

supported by an OLE DB data provider


supported by an ODBC data provider


supported by an Oracle data provider


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Session 4

The following properties and methods of a data adapter can

be used to perform various operations on a database:

SelectCommand

InsertCommand

UpdateCommand

DeleteCommand

Fill()

Update()


Refers to a DML statement or a stored procedure

to retrieve data from a database

Refers to a data command to insert data into adatabase

Refers to a data command to update a database

Refers to a data command to delete data from a

database

Fills the dataset with the records from a database

Executes the corresponding Insert, Update, or

Delete commands for each inserted, modified,

or deleted row to reflect the changes in a

database


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Session 4

Consider the following code snippet of creating aDataAdapter object and using the SelectCommand

property of the object:

SqlConnection cn = new

SqlConnection();

cn.ConnectionString = "Data

source=SQLSERVER01;Initial

catalog=HR;User id=sa;

Password=niit#1234";

DataSet DataSet1 = new DataSet();

SqlDataAdapter da = newSqlDataAdapter();

SqlCommand cmd=new SqlCommand

("Select * from Employees", cn);

da.SelectCommand = cmd;

da.Fill(DataSet1);


Set a connection string

Creating a DataSet object

Creating a SqlDataAdapter

object

Passing the SQL query to the

command object

Retrieving records from the

Employees tableFilling the dataset with records

from the Employees table


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A data adapter handles data transfer between the database

and the dataset through its properties and methods, and

displays data through the process of table mapping.

After a dataset has been created, the data adapter uses the

process of table mapping to map the columns in the

database table with the dataset columns.

A data adapter uses the TableMappings property, a

collection ofDatatableMapping objects that is used for

mapping between the database table and the DataTable

object in the dataset.



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A major challenge related to data access is that more than

one user might need to simultaneously access data in a

database.

Another challenge is more than one user might need to

access the data anytime, anywhere. This challenge can be

overcome by implementing database locking while a

transaction is executing.

However, if database locking is not implemented, it can lead

to data concurrency conflicts that arise from multiple

updates being performed on the database.



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Resolving data concurrency conflicts is a business decision,

with the following choices:

Prioritized on time; first update wins

Prioritized on time; last update wins

Prioritized on role

Prioritized on location

User resolves the conflict



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A significant way to increase the performance of data

updates is to update and send the changes to the database

in batches. This is known as batch updates.

Batch updates are performed by using theUpdateBatchSize property of the SqlDataAdapter

object.

By default, the UpdateBatchSize property is set to 1.

One way to confirm that the changes are being sent to thedatabase server in batches is to add a RowUpdated event

to theSqlDataAdapter

object. This event will show thenumber of rows affected in the last batch.



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Session 4

ADO.NET provides support for classes that can create any

provider-specific objects. These classes are known as theDbProviderFactories classes.

The DbProviderFactories class contains a method

called GetFactoryClasses that returns a data table,

which is populated with data from various providers, as

shown in the following figure.



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_______ class can create any data provider-specific object.

1. DbCommand

2. DbProviderFactories

3. DbParameter

4. DbConnection

Just a minute

Answer:

2. DbProviderFactories


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Session 4

Problem Statement:

The HR Manager of Tebisco needs to update the number of

vacancies, for those positions where the number of vacancies

is not more than 10. This updation will be based on the current

position code of employees.

As a part of the development team, you need to execute twoqueries, one to retrieve the number of vacancies per position

code, and the other to update the number of vacancies on the

basis of the current position code of employees.

You need to develop an application that can execute both

queries on a single database connection.

Hint: You need to access the InternalJobPosting and

Employee tables of the HR database.

Demo: Manipulating Data in a Connected Environment


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Session 4

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

Summary


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Session 4

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.

Summary (Contd.)


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Session 4

A data adapter, which is a part of the connected environment,

retrieves data from a database into a dataset.

The data adapters that can be configured to connect to a

database in Visual Studio .NET are:

SqlDataAdapter

OleDbDataAdapter

OdbcDataAdapter

OracleDataAdapter

Summary (Contd.)


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Session 4

The following properties and methods of a data adapter can be

used to perform the various operations on a database:

SelectCommand

InsertCommand

UpdateCommand

DeleteCommandFill()

Update()

A data adapter handles data transfer between the database

and the dataset through its properties and methods, and

displays the data through the process of table mapping.

Summary (Contd.)


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Resolving data concurrency conflicts is a business decision,

with the following choices:

Prioritized on time; first update wins

Prioritized on time; last update wins

Prioritized on role

Prioritized on locationUser resolves the conflict

A significant way to increase the performance of data updates

is to update and send the changes to the database in batches.

This is known as batch updates.

ADO.NET provides support for classes that can create any

provider-specific objects, such as SqlClient, Odbc,

OracleClient, and OleDb. These classes are known asDbProviderFactories classes.

Summary (Contd.)

Documents

Ddcauado.net Session04