chapter 14 - designing data access classes1 chapter 14 designing data access classes

Chapter 14 - Designing Data Access Classes 1

Chapter 14

Designing Data Access Classes


Making Objects Persistent Use object persistence to store instances or

attribute values for later retrieval Two approaches to achieving persistence:

Attribute storage – store the object’s attributes individually

Object storage – store the entire object

Advantage of object storage is that you don’t need to recreate the object when you retrieve it


Making Objects Persistent


Designing a Data Access Class The purpose of the Data Access (DA) class is

to provide methods to store and retrieve data and make instances of a Problem Domain (PD) class persistence

Three tier OO design GUI class PD class for business entities DA class for data storage and retrieval

DA class isolates data storage and retrieval DA class supports three-tier architecture


Data Access Methods Since you will not have instances of the DA

class – all methods will be static Four basic methods are provided

Retrieve – find method Store – addNew method Change – update method Remove – delete method


Data Access Methods


Communicating with DA Class The Customer class invokes methods in

CustomerDA class Isolates the DA class from everything but PD

class DA class methods are not tied to data

storage method

14


Finding a Customer The purpose of the PD find method is to

invoke the DA find method It’s a static method because it’s not tied to a

specific customer instance Throws a NotFoundException if the

customer is not found

14


Adding a Customer The purpose of the PD addNew method is to

invoke the DA addNew method It’s a non-static method because it’s invoked

for the new customer being added Throws a DuplicateException if the customer

already exists


Changing a Customer The purpose of the PD update method is to

invoke the DA update method It’s a non-static method because it’s invoked

for the customer being updated Throws a NotFoundException if the



Deleting a Customer The purpose of the PD delete method is to

invoke the DA delete method It’s a non-static method because it’s invoked

for the customer being deleted Throws a NotFoundException if the



Understanding Java I/O Java views data input and output as a flow

of bytes Two different data streams:

Byte stream Character stream

14


Understanding Java I/O14


Understanding Java I/O Record is a collection of related variables File is a collection of related records Sequential files contains records that are stored

and processed in sequential order Random access files are organized so you can

access a record by specifying its record number Database is one or more files that help make

queries Relational database organized in tables and rows

14


Implementing Persistence with a Sequential File Reads the customer records, creates a

customer instance for each record, and places instances in a Vector

Uses the java.io packageimport java.io.*;

14


Initialize Method Reads the attribute values for all of the

customers from the sequential file Uses BufferReader class to read the file

sequentially

14


Terminate Method Responsible for creating a file that contains

attribute values for all the customer instances in the Vector

Attributes written to the file using the println method

14


Find Method The find method simply iterates the

customers Vector, seeking a customer instance with a phone number that matches the value received by the method

If the customer is not found a NotFoundException is thrown


AddNew Method Simply adds the new reference to the Vector If a duplicate is found throws a

DuplicateException error


Update Method Contains no code – since the file is written

when done

14


Delete Method Remove a customer from the system Removes the reference from the Vector If the customer is not found a

NotFoundException is thrown

14


getAll Method The Vector already contains all of the

customers Simply returns this Vector


Testing CustomerDA Class1. Create two customer instances2. Invoke initialize3. Invoke addNew to add two customers4. Retrieve reference to first customer5. Invoke getAll6. Invoke delete7. Change first customer’s address and verify8. Invoke the terminate method

14


Implementing Persistence with Random Access Change the file specification to

Customer.ran Use the RandomAccessFile class Use the writeBytes method


Implementing Persistence with Object Serialization Store the entire Customer instances Change the file specification to

Customer.obj Use the ObjectInputStream and the

readObject method Use the ObjectOutputStream and the

writeObject method


Designing a Relational Database Provide tools to organize data into tables Each column represents a field Each row represents a record Each customer is identified by their phone

number – primary key Protocols required to access Microsoft

Access Java Database Connectivity (JDBC) Open Database Connectivity (ODBC) See pp. 510 for setup of DSN

14


Designing a Relational Database14


Understanding SQL Structured Query Language (SQL) used to access

relational databases SQL SELECT is used to retrieve a specific customer

record SQL INSERT is used to add a new customer record SQL UPDATE is used to change a customer record SQLQ DELETE is used to delete a customer record Java.sql package contains the database access

method

14


Understanding SQL 14

chapter 14 - designing data access classes1 chapter 14 designing data access classes

Documents