Emerging Technology Fall Semester, 2004 O/R Mapping Intro
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CS 683 Emerging Technologies Fall Semester, 2004 Doc 25 O/R Mapping Intro

Contents

References

Object O/R Mapping

SQL & Relational Tables

A GLORP Example

Person

Defining the Mapping

Creating the Table in the Database

Writing a Person to the Database

Reading from the Database

Modifying Objects

Copyright ©, All rights reserved. 2004 SDSU & Roger Whitney, 5500 Campanile Drive, San Diego, CA 92182-7700 USA. OpenContent ( http://www.opencontent.org/opl.shtml) license defines the copyright on this document.

References

Glorp web site http://glorp.org/

Glorp Tutorial, Roger Whitney

CS 580 Lecture notes, Roger Whitney

Object O/R Mapping

Examples

• GLORP (Smalltalk)

Generalized Lightweight Object-Relational Persistence

• Hibernate (Java)

SQL & Relational Tables

students

codes

mysql> CREATE TABLE students
   (
   firstname  CHAR(20) NOT NULL,
   lastname   CHAR(20),
   phone      CHAR(10),
   code_id       INTEGER
   );

mysql> CREATE TABLE codes
   (
   code       INTEGER,
   major       CHAR(20)
   );

SQL to access table

INSERT 
   INTO students (firstname, lastname, phone, code_id) 
SELECT
   'Roger' AS firstname,
   'Whitney' AS lastname,
   '594-3535' AS phone,
   codes.code AS code_id
FROM
   codes
WHERE
   codes.major = ‘Art’

SELECT
   firstname, lastname, phone, major
FROM
   codes, students
WHERE
   major = 'Art' AND code_id = code

JDBC

import java.sql.*;
   
public class SampleConnection 
   {
   static final String ART_MAJOR_SQL = " SELECT
         firstname, lastname, phone, major
      FROM
         codes, students
      WHERE
         major = 'Art' AND code_id = code”;
   
   public static void main (String args[]) throws Exception
      {
      Connection rugby = getDatabaseConnection();
      Statement getArtMajors = rugby.createStatement();
      ResultSet artMajorsRows = 
         getArtMajors.executeQuery(ART_MAJOR_SQL);
      ArrayList artMajors = new ArrayList();
      while (artMajorsRows.next() )
         {
         Student artMajor = new Student();
         artMajors.add( artMajor);
         artMajor.setFirstName(artMajorsRows.getString( “firstname”);
         artMajor.setLastName(artMajorsRows.getString( “lastname”);
         artMajor.setPhone(artMajorsRows.getString( “phone”);
         artMajor.setMajor(artMajorsRows.getString( “major”);
         }
      doSomethingWithArtMajors(artMajors);
      rugby.close();
      }

JDBC Example Continued

   Connection getDatabaseConnection() throws SomeTypeOfException
      {
      String dbUrl = "jdbc:mysql://rugby.sdsu.edu:8777/test";
      String user = "whitney";
      String password = "mylittleSecret";
   
      Class.forName("com.mysql.jdbc.Driver");
      return DriverManager.getConnection( dbUrl, user, password);
      }
   }

A GLORP Example

Person

Smalltalk defineClass: #Person
   superclass: #{Core.Object}
   indexedType: #none
   private: false
   instanceVariableNames: 'firstName lastName '
   classInstanceVariableNames: ''
   imports: ''
   category: 'GlorpExperiments' 
   

Person class methods

first: firstNameString last: lastNameString
   ^self new setFirst: firstNameString last: lastNameString   

Person instance methods

setFirst: firstNameString last: lastNameString
   firstName := firstNameString.
   lastName := lastNameString 
   
firstName: anObject 
   firstName := anObject  

Defining the Mapping

Smalltalk defineClass: # GlorpTutorialDescriptor
   superclass: #{Glorp.DescriptorSystem}
   indexedType: #none
   private: false
   instanceVariableNames: ''
   classInstanceVariableNames: ''
   imports: 'Glorp.DirectMapping'
   category: 'GlorpExperiments' 
   
GlorpTutorialDescriptor >>allTableNames
   ^#( 'PEOPLE' )
   
tableForPEOPLE: aTable 
   aTable createFieldNamed: 'first_name' type: (platform varChar: 50).
   (aTable createFieldNamed: 'last_name' type: (platform varChar: 50)) bePrimaryKey.
   
descriptorForPerson: aDescriptor
   
   | table |
   table := self tableNamed: 'PEOPLE'.
   aDescriptor table: table.
   (aDescriptor newMapping: DirectMapping) 
      from: #firstName
      to: (table fieldNamed: 'first_name').
   (aDescriptor newMapping: DirectMapping) 
      from: #lastName
      to: (table fieldNamed: 'last_name')

Defining the Mapping Continued

classModelForPerson: aClassModel
   aClassModel newAttributeNamed: #firstName.
   aClassModel newAttributeNamed: #lastName.
   
constructAllClasses
   ^(super constructAllClasses)
      add: Person;
      yourself

Creating the Table in the Database

login := Login new database: PostgreSQLPlatform new;
   username: 'whitney';
   password: 'foo';
   connectString: '127.0.0.1_glorpTests'.
   
accessor := DatabaseAccessor forLogin: login.
accessor login.
   
session := GlorpSession new.
session system: 
   (GlorpTutorialDescriptor forPlatform: login database).
session accessor: accessor.
   
session inTransactionDo:
   [session system allTables do: 
      [:each | 
      accessor  
         createTable: each 
         ifError: [:error |Transcript show: error messageText]]].

One does not have to use GLORP to create tables in the database. One can create them by hand. In many cases that will be the case.

Writing a Person to the Database

person := Person first: 'Pete' last: ‘Frost’.
session beginUnitOfWork.
session register: person.
session commitUnitOfWork.

All objects registered in a unit of work (and with the proper GLORP mapping) will be written to the database in the correct table(s) when the unit of work is completed

Reading from the Database

Reading all Rows

people := session readManyOf: Person .

people will be a collection of Person objects.

Reading one Person

foundPerson := session 
                           readOneOf: Person 
                           where: [:each | each firstName = 'Jose'] 

Modifying Objects

session beginUnitOfWork.
foundPerson := session 
                           readOneOf: Person 
                           where: [:each | each firstName = 'Jose'].
foundPerson firstName: 'RamJet'.
session commitUnitOfWork

Any object read from the database in a unit of work is automatically registered with the using of work. Any object registered with a unit of work that is modified during the unit of work will have the modifications saved to the database when the unit of work is committed. The proper rows in all required tables are updated.

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