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Assembling Chapter a Three-Tier Windows Application
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Objectives
In this chapter, you will:
Review three-tier design
Combine a problem domain class, a data access class, and a GUI
Use multiple GUIs and add an instance to a database Use GUIs with multiple problem domain classes to interact with a database
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Reviewing Three-Tier Design
Three-tier design
An architecture for structuring OO applications The three tiers
GUI classes Problem domain classes Data access classes
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Reviewing Three-Tier Design
In three-tier design
User interacts with GUI class instances GUI instances interact with problem domain classes and instances Problem domain classes and instances interact with data access classes Data access classes handle storing and retrieving data from files or databases
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Reviewing Three-Tier Design
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Reviewing Three-Tier Design
Benefits of three-tier design
System maintenance is simplified Applications can be distributed across the network
Three-tier design lends itself to client-server architectures
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Three-Tier Design and the Development Process
OO system development is done iteratively
Some analysis, some design, and some implementation occurring before continuing with more analysis, more design, and more implementation
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Three-Tier Design and the Development Process
OO system analysis
Define the requirements for the system
Use cases
Each use case is expanded into multiple scenarios
Scenarios define the functions the system provides
Problem domain classes
Initially defined in terms of
Attributes A few key methods
Additional details are added during each iteration
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Three-Tier Design and the Development Process
OO system design
Add details that specify how the system will be physically implemented Examples
User interface design Physical design of the database
OO system implementation
Write code to define
Problem domain classes GUI classes Data access classes
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Three-Tier Design and the Development Process
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Combining a PD class, a DA class, and a GUI
First three-tier example
Involves
Customer problem domain class from Chapter 13 Customer data access class from Chapter 13 FindCustomer GUI from Chapter 11
FindCustomer GUI retrieves information about a specific customer
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Combining a PD class, a DA class, and a GUI
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Reviewing the Customer Problem Domain Class
Customer problem domain class from Chapter 13
Used by this example Includes
Four class methods
Initialize Terminate GetAll Find
Three instance methods
AddNew Update Delete
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Reviewing the Customer Problem Domain Class
Customer problem domain class from Chapter 13 (continued)
DA methods pass requests to the CustomerDA class, when invoked
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Reviewing the Customer Data Access Class
CustomerDA class
Implements the details associated with the data access methods in the Customer class Throws exceptions if
A new customer already exists A customer that is to be deleted or updated cannot be found
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Reviewing the Customer Data Access Class
CustomerDA class from Chapter 13
Requires no changes for use in this three-tier example A modification done for convenience
The database file (CustomerDatabase.mdb) is placed within the project's bin folder
Enables the removal of the hard-coded path to the data source from the code
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Updating the FindCustomer GUI
FindCustomer GUI
Introduced in Chapter 11, Example 4 Used for the final tier of this example Requires only a few minor modifications to work with the Customer and CustomerDA classes
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Updating the FindCustomer GUI
Required modifications
Constructor
Must initialize the database
Reason: This example does not include a MainMenu GUI
PopulateListBox method
Invokes the GetAll method of the Customer class
To retrieve customer instances from the database for populating the list box
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Updating the FindCustomer GUI
Required modifications (continued)
btnUpdate_Click method
Invokes the Update method of the Customer class
To update customer information in the database
The Enabled property of the CustomerPhone text box is set to False
Reason: Customer phone number is the primary key for the customer table
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Updating the FindCustomer GUI
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Updating the FindCustomer GUI
Required modifications (continued)
btnClose_Click method
Terminates the connection to the database
Reason: This example does not include a main menu GUI
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Using Multiple GUIs and Adding an Instance to the Database
Second three-tier example
Uses multiple GUIs Adds an instance to the database using a data access class Based on Example 4 in Chapter 11 Contains a main menu, which allows the user to
Find a customer Add a new customer
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Using Multiple GUIs and Adding an Instance to the Database
Classes involved
FindCustomer GUI from previous example in this chapter
Modified slightly to work with the main menu
AddCustomer GUI from Chapter 11
Modified slightly to work with the data access classes
MainMenu GUI from Chapter 11
Modified slightly to work with the data access classes
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Using Multiple GUIs and Adding an Instance to the Database
Classes involved (continued)
Custom exceptions
NotFoundException DuplicateException
Customer class defined in the previous example
Does not have to modified
be CustomerDA class defined in the previous example
Does not have to be modified
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Using Multiple GUIs and Adding an Instance to the Database
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Reviewing the MainMenu GUI
MainMenu GUI class of Chapter 11
Only two minor changes are needed for this example
Invokes the Initialize method of the Customer class
To establish the connection to the database
Invokes the Terminate method of the Customer class
To terminate the connection to the database
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Reviewing the AddCustomer GUI
AddCustomer GUI
First introduced in Chapter 11 Modifications for this example
btnAdd_Click method
Invokes the AddNew method of the Customer class (rather than the CustomerData class)
Allows AddCustomer to work with data access classes
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Updating the FindCustomer GUI
FindCustomer GUI class used in the previous example
Modifications required for this example
The statement that invokes the Initialize method is removed
In this example, the MainMenu GUI establishes the connection to the database
The statement that invokes the Terminate method is removed
In this example, the MainMenu GUI terminates the connection to the database
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Using GUIs with Multiple Problem Domain Classes
Third three-tier example
Combines multiple GUIs with multiple problem domain and data access classes Contains
GUIs seen in this chapter and in Chapter 11
MainMenu FindCustomer AddCustomer AddBoat
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Using GUIs with Multiple Problem Domain Classes
Third three-tier example
Contains (continued)
Classes from Chapter 14
Customer CustomerDA Boat BoatDA CustomerAndBoatDatabaseConnect
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Using GUIs with Multiple Problem Domain Classes
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Reviewing the Customer and Boat PD and DA Classes From Chapter 14
This example uses the chapter 14 versions of the following classes without modifications
Customer problem domain class Customer data access class Boat problem domain class Boat data access class CustomerAndBoatDatabaseConnect class
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Reviewing the Customer and Boat PD and DA Classes From Chapter 14
Association relationship between Customer and Boat
Multiplicity: one-to-one in both directions Established by including
A Boat reference variable in Customer A Customer reference variable in Boat Accessor methods for the Boat and Customer references
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Reviewing the Customer and Boat PD and DA Classes From Chapter 14
CustomerAndBoatDatabase.mdb from Chapter 14
A relational database Includes two tables:
CustomerTable BoatTable
Foreign key: CustomerPhoneNo
Allows the two tables to be joined
Used without modifications in this example
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Modifying the MainMenu GUI
MainMenu GUI
Opens and closes the connection to the database Constructor
Invokes the Initialize method of the CustomerAndBoatDatabaseConnect class
To establish the common connection
Shares this connection by passing it to the Initialize methods of
Customer class Boat class
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Modifying the MainMenu GUI
MainMenu GUI (continued)
btnClose_Click procedure
Closes the connection to the database
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Modifying the FindCustomer GUI
FindCustomer GUI from the previous example
Modifications required for this example
A Boat reference variable is included in the class definition
Reason: FindCustomer must now recognize the association between Customer and Boat
lblBoatInfo label is added to the btnFind_Click method
lblBoatInfo label holds information about the customer's boat
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Reviewing the AddCustomer GUI from Chapter 11
AddCustomer GUI presented in Chapter 11
Used without modifications in this example Validates customer information entered by the user Creates a corresponding instance of Customer Passes the newly created Customer instance to the AddBoat GUI as an argument
AddBoat GUI
Captures information about the customer's boat Adds the customer information to CustomerTable Adds the boat information to BoatTable
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Modifying the AddBoat GUI
AddBoat GUI from chapter 11
Constructor: receives a Customer reference variable in the parameter list Validates the boat information entered by the user Creates a corresponding instance of Boat Establishes the two-way association between the customer and boat instances
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Modifying the AddBoat GUI
In this three-tier example, AddBoat must now
Add the boat record to BoatTable Add the associated customer record to CustomerTable
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Modifying the AddBoat GUI
Modifications needed for this example
AddSailboat method
Creates an instance of the Boat class, rather than an instance of Sailboat Invokes the AssignBoatToCustomer method of the Boat class
AddPowerboat method
Creates an instance of the Boat class, rather than an instance of Powerboat Invokes the AssignBoatToCustomer method of the Boat class
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Summary
Three-tier design is a strategy for creating OO applications that are easy to maintain Three-tier design provides a framework that lends itself to iterative development In iterative development, some analysis, some design, and some implementation are completed and then the process repeats with more analysis, more design, and more implementation
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Summary
First example: demonstrated one GUI, one PD class, one DA class, and a database with one table Second example: used multiple GUIs (including MainMenu, AddCustomer, and FindCustomer), one PD class and one DA class Third example: used multiple GUIs, two PD classes with an association relationship, two DA classes, and a database with two tables
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