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CH 12 WORKING WITH DATABASES

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12.1 Introduction

Database - Organized collection of data

Database management system (DBMS) Software that provides

mechanisms for storing, organizing, retrieving and modifying data

Visual Basic programs communicate with databases and manipulate

their data through ADO.NET (Active Data Objects - technology usedto interact with a database)

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12.2 ADO.NET Object Model

ADO.NET Provides an API for accessing database systems

programmatically. For those familiar with previous technologies ADO.NETreplaces Microsoft's ActiveX Data Objects (ADO) technology.

DataSets - Represents cached data from the data source. It can beused when the application is disconnected from the database. As adataset does not need a persistent connection to work with data onecan connect to the data source to populate the DataSet, and

disconnects immediately afterwards then continue working. Later on ifnecessary then one can reconnect to perform an update and thendisconnect

Connection - Represents a connection of dataset to a database

DataAdapter It populates and update the DataSet with data from thedata base and vice versa by executing commands/Query statementsgiven (in SQL)

CommandsUsed by the data adapter to know what to retrieve fromoradd to the database

Data BaseData SetApplication Data Adapter

For Connection

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12.3 Integrated Development Environment (IDE)

The IDE provides visual programming tools and wizards that simplifyaccessing data in your projects. These tools establish databaseconnections and create the ADO.NET to view and manipulate thedata through GUI controls

Connection string - Specifies the path to a database file. It

determine how the database is accessed Data Set - Adding a data source causes the IDE to generate a

dataset to store data from that data source

DataGridView component - Displays a data source in a GUIorganized in rows and columns

BindingNavigatorcomponent. Provides several ways for users tobrowse and manipulate data displayed by another GUI control on aForm

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Example on IDE

Here we use a Wizard to create a programme that reads the

database and allows us to scroll through it.

Start by designing the database below:


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Open a new windows application and

click on and click on the data

sources tab at the bottom of thesolution explorer

Click on add new database

Select the database option and clickon next

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We need to select the data

connection object. Click on new

connection.

The Microsoft Access Database

File (OLE DB) data source

appears by default, this is for Ms

Access 2003. Click on change.

The object for Ms Access 2007

will be under the options shown

below


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Select the following OLE DB

provider. This is the engine for

MS Access 2007.

Write the full path of the file

and the file name.

Test connection If you get the

message below then you can

proceed, otherwise fix the

problem first.


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The connection has been

created. We now need to save

the connection. Give your

connection string any nameyou like

Select the objects you would

like added to your dataset. In

our example we only need the

two fields ENO & ENAME

under table employee.

Give the dataset a name


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When you are returned to your form, you should notice the Solution

Explorer has added your a Data Set.

Your data set will be your source of data for the application.

The dataset in turn gets data from the database

To add a Field to your Form, click on one in the list. Hold down your leftmouse button, and drag it over to your form.


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Notice the IDE automatically creates: Labels & Textboxes To display he data

A Binding Source links a textbox to the

correct field

A navigation bar To help you scroll

through the data

A data adapter To populate the datasetwith data from the database


Run your program!

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While the IDE is easy, you are limited to making use of what it gives

you.

Often you want to customize your application to do a little more.

Writing your own database code then becomes a better option.

We now look at how to write our own code


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NB: Design a database before attempting to connect to it.

12.5 Write your own Database code

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Instead of using the IDE you can write your own DB code. In thisUnit we look at how to write your own code.

The aim is to gain a deeper understanding of programmingconcepts in order to understand what happens behind the scenes.

You will have to write code for the following tasks that were

discussed earlier:

1. Connection

2. Data Set

3. Data Adapter

4. Commands

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12.6 Design the Interface


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12.7 Declare Required Components


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7. Write code to populate the text boxes with data from the data set

12.8 Display Data from your Data base


Commands

1. Specify the database application and the database

2. Open the connection

Connection

3. Write commands (SQL Statements) specifying what to read

4.Tell the adapterthe database connection and the commands required

5. Tell the adapterto populate the data set

6. Close the connection


For Connection


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Write the following code in the click event for the display button


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12.9 Navigating the Data Set

We need to write code for the Back and Next buttons. Since we are

manipulating the data set we do not need the data adapter this time. We need to know the number of records in the data set so that we

can inform the user when they reach the end. A variable can becreated for this (We can call it maxrow).

We also need a variable to help us know the record we are currentlyon (We can call it inc).

The following steps apply:1. Declare the two variables


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2. Initialize the variables.

We need to have connected to the database before attempting to

navigate.

Since the display event did this for us we can avoid duplicating the

connection code by forcing the user to click on display before

attempting to navigate. This can be achieved by disabling all otherbuttons except the display button when the form loads. Thus the

following code should be written for the form load event.


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Initializing of our variables should then be done within the display

event as follows


Provider=Microsoft.ACE.OLEDB.12.0;Data Source = Employee.accdb


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3. Write Code for the Buttons Click Events


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12.10 Editing a record

When a record is edited the database needs to be updated and as a

result we need the data adapterto help us update it. Additionally we need a command builderevery time we need to

write to the database. Command Builder will build a SQL string foryou.

Steps:

1. Create a command builder

2. Write the changes on the controls to the data set3. Write the data in the data set to the database


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12.11 Writing data to a Database

To Do this:

1. Clear the Controls

In our example the button Add will be used to clear the controls


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2. Create a command builder

3. Create a new row

4. Add data from controls to new row

5. Add new row to data set

6. Write the data to a database

In our example we will use the save button to do the above


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Write the following code for the save button


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12.12 Deleting a record from the data base

Again we need to make changes to the data base hence we will

require the data adapter and the command builder Steps:

1. Create the command builder

2. Delete the row

3. Change to focus to another row e.g. the first row


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12.13 Sequencing Procedures

Notice if you attempt to edit an empty record you will get an error!

Some task need to be done in a specific order. You can disable controls to ensure that the user does not do

something that is not expected.

For example the following code can be inserted in the form load

event to ensure that the user can only click on display command first

before doing anything else.


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You must however remember to enable the buttons within the

display buttons click event, otherwise the user will not be able to

click anything else within the program.


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Exercise I

Design the database below:


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Design the interface below and write code to implement theapplication


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Exercise II

Design the system below

Documents

IST 2020 CH 12