	CS 535 Object-Oriented Programming Fall Semester, 2003 Saving Data in Files
	Previous Lecture Notes Index © 2003, All Rights Reserved, SDSU & Roger Whitney San Diego State University -- This page last updated 04-Dec-03

Contents of Doc 18, Saving Data in Files

References

VisualWorks Developer’s Guide, Chapter 21 Binary Object Files

OmniBase documentation, http://www.gorisek.com/homepage/index.html


Doc 18, Saving Data in Files Slide # 2

Saving Data in Files

Some Issues

ASCII verses Binary Files
Extracting data from objects verse saving objects
Multiple program access of data
Concurrent access to data file
Nested Objects
Circular references
Handling changes in class of a saved object
Searching for data in the saved file
Updating file after change of object


Doc 18, Saving Data in Files Slide # 3

Handling changes in class of a saved object
Save an object or data in an object to a file

Modify the class by:

Adding methods
Removing methods
Adding instance variables
Removing instance variables
Renaming instance variables
Reordering instance variables

Read the data in the file

Recreate the object

What happens?

In Smalltalk adding/removing methods does not affect recreating the object


Doc 18, Saving Data in Files Slide # 4

Customer Class Used in Examples

Smalltalk defineClass: #Customer
   superclass: #{Core.Object}
   indexedType: #none
   private: false
   instanceVariableNames: 'name phone id '
   classInstanceVariableNames: 'nextId '
   imports: ''
   category: 'Course-GUI-Examples'

"-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- "!

Customer class methods

name: nameString phone: phoneString
   ^self new 
      name: nameString;
      phone: phoneString;
      id: self nextId

nextId
   nextId ifNil: [nextId := 0].
   ^nextId := nextId + 1.


Doc 18, Saving Data in Files Slide # 5

Instance Methods

= aCustomer
   ^(name = aCustomer name) & 
   (phone = aCustomer phone) & 
   (id = aCustomer id)

id
   ^id

id: anInteger
   id := anInteger

name
   ^name

name: aString
   name := aString

phone
   ^phone

phone: aString
   phone := aString


Doc 18, Saving Data in Files Slide # 6

Simple Text Files

Let an Object know how to save/restore itself

Convert instance variables to strings

Use characters to separate instance variables

Saving

Customer>>saveOn: aStream 
   aStream
      nextPutAll: name;
      nextPut: self fieldSeparator;
      nextPutAll: phone;
      nextPut: self fieldSeparator;
      nextPutAll: id printString;
      nextPut: self objectTerminator

Customer>>objectTerminator
   ^Character cr

Customer>>fieldSeparator
   ^$,

Restoring

Customer class>>readFrom: aStream
   ^super new readFrom: aStream

Customer>>readFrom: aStream
   name := aStream upTo: self fieldSeparator.
   phone := aStream upTo: self fieldSeparator.
   id := (aStream upTo: self objectTerminator) asNumber


Doc 18, Saving Data in Files Slide # 7

Sample UseSaving

   | out customers dataFile |
   dataFile := 'dataFile.txt' asFilename.
   out := dataFile writeStream.
   customers := (OrderedCollection new)
      add: (Customer name: 'roger' phone: '1234567');
      add: (Customer name: 'pete' phone: '1111111');
      add: (Customer name: 'jose' phone: '2222222');
      yourself.
   customers do: [:each | each saveOn: out].
   out close.

Restoring

   | customers in dataFile |
   dataFile := 'dataFile.txt' asFilename.
   in := dataFile readStream.
   customers := OrderedCollection new.
   [in atEnd] whileFalse: [customers add: (Customer readFrom: in)].

dataFile.txt Contents

roger,1234567,34
pete,1111111,35
jose,2222222,36


Doc 18, Saving Data in Files Slide # 8

Issues
What characters to use to separate instance variables?
What character to use to end an object data?
How to handle nested objects?
What happens when you add/remove instance fields to the class?

Properly selected separators allow other programs to manipulate data files


Doc 18, Saving Data in Files Slide # 9

StoreString – Saving Objects in ASCII

storeString
   "Answer a String representation of the receiver from which 
   the receiver can be reconstructed."

Automatically serializes objects into strings

No need to add code to existing classes

This is appropriate only for smaller simpler objects.

Can handle nested objects

Cannot handle circular references of objects.

Uses order of instance variables, can handle

Adding new instance variables at end
Renaming instance variables

Cannot handle

Reordering of instance variables
Removing of instance variables
Adding instance variable in the middle of the variable list

Calls storeOn: to perform work (in case you want to modify it)


Doc 18, Saving Data in Files Slide # 10

Saving

   | out customer dataFile |
   dataFile := 'dataFile.txt' asFilename.
   out := dataFile writeStream.
   customer := Customer name: 'roger' phone: '1234567'.
   customer storeOn: out.
   out close.

Restoring

   |  contents customer dataFile |
   dataFile := 'dataFile.txt' asFilename.
   contents := dataFile contentsOfEntireFile.
   customer :=Compiler evaluate: contents.
   customer inspect

dataFile.txt Contents (Customer basicNew instVarAt: 1 put: 'roger'; instVarAt: 2 put: '1234567'; instVarAt: 3 put: 37; yourself)


Doc 18, Saving Data in Files Slide # 11

storeString Nested Object Example

Saving

   | out customers dataFile |
   dataFile := 'dataFile.txt' asFilename.
   out := dataFile writeStream.
   customers := (OrderedCollection new)
      add: (Customer name: 'roger' phone: '1234567');
      add: (Customer name: 'pete' phone: '1111111');
      add: (Customer name: 'jose' phone: '2222222');
      yourself.
   out          
      nextPutAll: customers storeString;
      close
   “Could also use customers storeOn: out”

Restoring

   |  contents customers dataFile |
   dataFile := 'dataFile.txt' asFilename.
   contents := dataFile contentsOfEntireFile.
   customers :=Compiler evaluate: contents.

dataFile.txt Contents ((Core.OrderedCollection new) add: (Customer basicNew instVarAt: 1 put: 'roger'; instVarAt: 2 put: '1234567'; instVarAt: 3 put: 39; yourself); add: (Customer basicNew instVarAt: 1 put: 'pete'; instVarAt: 2 put: '1111111'; instVarAt: 3 put: 40; yourself); add: (Customer basicNew instVarAt: 1 put: 'jose'; instVarAt: 2 put: '2222222'; instVarAt: 3 put: 41; yourself); yourself)


Doc 18, Saving Data in Files Slide # 12

What happens when you change an object?
You must save it again

If saved in a collection must save the entire collection

   |  contents customers dataFile |
   dataFile := 'dataFile.txt' asFilename.
   contents := dataFile contentsOfEntireFile.
   customers :=Compiler evaluate: contents.
   customers first name: ‘foo’.
   out := dataFile writeStream.
   customers storeOn: out.
   out close.


Doc 18, Saving Data in Files Slide # 13

BOSS – Binary Object Storage System

Stores objects in binary

Handles nested objects

Handles circular references of objects

Very sensitive to changes in Class

You must provide code to convert between old and new format

Need to load the BOSS parcel

In the Parcel Manager it is located in Application development

See Chapter 21 Binary Object Files in VisualWorks Developer’s Guide


Doc 18, Saving Data in Files Slide # 14

Storing

   | bos customers dataFile |
   dataFile := 'dataFile.txt' asFilename.
   bos  := BinaryObjectStorage onNew: dataFile writeStream.
   customers := (OrderedCollection new)
      add: (Customer name: 'roger' phone: '1234567');
      add: (Customer name: 'pete' phone: '1111111');
      add: (Customer name: 'jose' phone: '2222222');
      yourself.
   [bos nextPutAll: customers] ensure: [bos close]

Restoring

   |  customers dataFile |
   dataFile := 'dataFile.txt' asFilename.
   bos  := BinaryObjectStorage onOldNoScan: dataFile readStream.
   [customers := bos contents] ensure: [bos close].

Searching the file

   |  nextCustomer dataFile |
   dataFile := 'dataFile.txt' asFilename.
   bos  := BinaryObjectStorage onOldNoScan: dataFile readStream.
   [[bos atEnd]
      whileFalse: 
         [nextCustomer := bos next.
         nextCustomer name = 'pete' ifTrue:[^nextCustomer]]] 
   ensure: [bos close]
Doc 18, Saving Data in Files Slide # 15

What happens when you change an object?
You must save it again

If saved in a collection must save the entire collection


Doc 18, Saving Data in Files Slide # 16

XML Configuration Files

Download from main course page

Stores objects using XML

Handles nested objects

Handles circular references of objects

Very tolerant of changes in class of stored objects

Uses name of instance variable to restore object, so can

Add instance variable
Remove instance variables
Reorder instance variables

Note the full name of the class is Tools.XMLConfigFileSupport.XMLConfigFile


Doc 18, Saving Data in Files Slide # 17

Saving Multiple Objects

   |  xmlFile |
   xmlFile :=XMLConfigFile filename: 'dataFile.txt'.
   xmlFile 
      saveObject: (Customer name: 'roger' phone: '1234567');
      saveObject: (Customer name: 'pete' phone: '1111111');
      saveObject: (Customer name: 'jose' phone: '2222222');
      saveConfiguration.

Restoring

   |  xmlFile objects customer1 customer2  customer3 |
   xmlFile :=XMLConfigFile filename: 'dataFile.txt'.
   objects :=xmlFile loadConfiguration.
   customer1 := objects first.
   customer2 := objects at: 2.
   customer3 := objects at: 3
Doc 18, Saving Data in Files Slide # 18

Saving a Collection

   |  xmlFile |
   xmlFile :=XMLConfigFile filename: 'dataFile.txt'.
   customers := (OrderedCollection new)
      add: (Customer name: 'roger' phone: '1234567');
      add: (Customer name: 'pete' phone: '1111111');
      add: (Customer name: 'jose' phone: '2222222');
      yourself.
   xmlFile 
      saveObject: customers;
      saveConfiguration.

Restoring

   |  xmlFile |
   xmlFile :=XMLConfigFile filename: 'dataFile.txt'.
   objects :=xmlFile loadConfiguration.
   customers := objects first.
Doc 18, Saving Data in Files Slide # 19

OmniBase – Object Database

Handles nested objects

Handles circular references of objects

Very tolerant of changes in Classes of stored objects.

Can search for an object

Edit and save one object with having to resave all objects

Handles concurrent access

Supports transactions with rollback

Do not need separate database process

Download educational version at: http://www.gorisek.com/homepage/index.html


Doc 18, Saving Data in Files Slide # 20

Creating

   |  database |
   database :=OmniBase createOn: 'data'.
   database close.

You can create and use the database before closing
Creating is done once, so I do it here to get to over with

Simple adding to Database


   |  database |
   database :=OmniBase openOn: 'data'.
   [ OmniBase root
      at: 'test'
      put: (OrderedCollection newPersistent
         add: 'string object';
         add: 1;
         add: Date today;
         yourself) ] evaluateAndCommitIn: db newTransaction.

Accessing

   |  database date |
   database :=OmniBase openOn: 'data'.
   [ date:= (OmniBase root at: 'test') last ] evaluateIn: database newTransaction.
   ^date


Doc 18, Saving Data in Files Slide # 21

Modifying
Modifying the collect at test

   |  database test |
   database :=OmniBase openOn: 'data'.
   [ test:=  (OmniBase root at: 'test'). 
   test add: 'Hi Mom'.
   test markDirty] evaluateAndCommitIn: database newTransaction.
   database close.

Don’t have to resave all objects in the file

Object needs to be persistent and marked dirty


Doc 18, Saving Data in Files Slide # 22

Customer ExampleAdding the Customers

   |  database customers |
   database :=OmniBase openOn: 'data'.
   customers := (OrderedCollection new)
      add: (Customer name: 'roger' phone: '1234567');
      add: (Customer name: 'pete' phone: '1111111');
      add: (Customer name: 'jose' phone: '2222222');
      yourself.
   [customers makePersistent.
   customers do: [:each | each makePersistent]. 
   OmniBase root
      at: 'customers'
      put: customers ] evaluateAndCommitIn: database newTransaction.
   database close.

Accessing and Modifying a Customer

   |  database customers toChange  |
   database :=OmniBase openOn: 'data'.
   [customers :=  OmniBase root at: 'customers'. 
   toChange := customers detect: [:each | each name = 'pete'].
   toChange phone: '9999999'.
   toChange markDirty]
       evaluateAndCommitIn: database newTransaction.
   database close.

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