Building multitiers program doc

Creating methods: Write constructors A constructor is a special method that used to initialize the properties of the object  A constructor is invoked when the object gets instantiated

Building multitiers program

Week 9

1. Review OOP

2. Three-tier application

3. Implementing 3-tier

Create class

 Add new class: menu Project->Add Class

 Create properties for a class

 Create methods for a class

 Create events for class

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Creating properties for a class

 Declare all variables in a class as private (encapsulation)

 private properties must be assigned values and can be get values

 through get/set

public dataType myProperty {

get { return propertyName; }

set { propertyName = value; } }

Creating methods: Write constructors

 A constructor is a special method that used to initialize the properties of the object

 A constructor is invoked when the object gets instantiated

 Note to write a constructor:

the same

 A constructor does not return value, not even void

 A class can have multiple constructors (overloaded

constructors)

public ClassName (parameterList)

{ }

Instantiating an object

 To instantiate an object, using the new keyword

 Example:

Lop l = new Lop();

Lop c;

c = new Lop(“NCTH2K”, “Cao dang nghe 2K”);

ClassName object = new ClassName (…);

ClassName object;

object = new ClassName (…);

Using properties, methods of a class

 Call methods or properties of a class

 Using dot operator

 get: variable = object.propertyName

 set: object.propertyName = variable

 Example:

SinhVien sv = new SinhVien();

sv.HoTen = “Nguyen Van An”;

sv.DiemLT = 5;

sv.DiemTH = 10;

lblTB.Text = sv.DiemTB().ToString();

MessageBox.Show(sv.HoTen + “ có ĐTB = ” + sv.DiemTB());

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1. Review OOP

2. Three-tier application

3. Implementing 3-tier

2 Three-tier application

2.1 What is a 3-tier architecture?

2.2 What is the need for dividing the code in 3-tiers?

2.3 Designing 3-tier

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2.1 What is a 3-tier architecture?

 Three-tier (layer) is a client-server

architecture in which the user

interface, business rules and data

access are developed and maintained

as independent modules

 There are:

 Tier 1: Presentation tier

 Tier 2: Business Logic tier

 Tier 3: Data Access tier

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2.2 What is the need for dividing the code in 3-tiers?

 Reusability

 E.g if we have a module that handles adding, updating, deleting and finding customers in the system, we can use it in any

other project that might involve maintaining customers

 Transformation of the system is easy

there shouldn’t be any changes required in the business layer component and in the GUI component.

 Change management of the system is easy

to update the business logic component

2.3 Designing 3-tiers:

Data Access layer

 The Data Access Logic component provide methods for querying and updating data (relational databases, file

system,…)

 Each Data Access Logic component typically provides

methods for inserting, deleting, updating and retrieving

operations relating to a specific business entity in the

application

 When the application contains multiple Data Access Logic components, you may use a generic data access component

to manage database connections, execute commands,…

2.3 Designing 3-tiers:

Data Access layer

DACommon

- conn : OleDbConnection

+ getTable( sql: string ) : DataTable

+ Update( tableUpdate : DataTable , tableName : string ):

void

Customers

- dacommon : DACommon

+ getTable() : DataTable

+ insert (fields in database) : bool

+ delete (primary fields in database) : bool

+ update (fields in database) : bool

+ find (some fields in database) : DataTable

Products

- dacommon : DACommon + getTable() : DataTable + insert (fields in database) : bool + delete (primary fields in database) : bool + update (fields in database) : bool

+ find (some fields in database) : DataTable

2.3 Designing 3-tiers:

Business Logic layer

 The Business Logic layer contains classes that handle the data

 Functionality

 To call Data Access Logic components to retrieve and/or update application data

 Calculations

 Validation to enforce business rules

2.3 Designing 3-tiers:

Presentation layer

 The Presentation layer contains the components that are required to enable user interaction with the application  User Interface

 Functionality

 Receive and send data to the business logic tier

 Restrict the types of input a user can enter

information provided by the user controls to values needed

by the underlying components

1. Review OOP

2. Three-tier application

3. Implementing three-tier

 Window Application

 Class Library

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