From: "Michael S.Jessop" <candiazoo@...>
Date: 2005-11-16T08:37:18+09:00
Subject: Baffled by error

I am playing around...  I am a ruby newbie.  I am encountering an error 
I can't figure out.  Probably something very silly I am doing wrong...

I have a class called "Artist" (I'll attach it below) that tries to 
open an SQLite3 database and load a row into itself.

As I code I keep a "test.rb" around to try things out.  In the test.rb 
I require, open and execute a query successfully.  I add a reference to 
my class and try its load method and get this:

Mitchs-iMac-G5:~/Desktop/Projects/ArtManagerRuby mike$ ruby test.rb
1
Painting
Landscape
Oil
Canvas
Farmlands
This is a comment
3
Painting
Landscape
Watercolor
Paper
She kicks ASS!
Not only is her artwork the best, she is my wife!
4
Sketch
Landscape
Crayon
Paper
Loves the beach!
This guy can color with crayola crayons like nobody I have ever seen!
"stuff"
"done!"
"nope"
true
"yah baby!"
"this is a catenated string"
/opt/local/lib/ruby/vendor_ruby/1.8/sqlite3/database.rb:619:in 
`const_get': uninitialized constant SQLite3::Driver::Native (NameError)
        from 
/opt/local/lib/ruby/vendor_ruby/1.8/sqlite3/database.rb:619:in 
`load_driver'
        from 
/opt/local/lib/ruby/vendor_ruby/1.8/sqlite3/database.rb:616:in `each'
        from 
/opt/local/lib/ruby/vendor_ruby/1.8/sqlite3/database.rb:616:in 
`load_driver'
        from 
/opt/local/lib/ruby/vendor_ruby/1.8/sqlite3/database.rb:107:in 
`initialize'
        from ./artist.rb:100:in `new'
        from ./artist.rb:100:in `load'
        from test.rb:41

-----------

(The output at first is the successful accessing of the database, the 
error is when I call the load method of my class)

Here is the test.rb file:

require 'sqlite3'
require 'db_base'
require 'artist'

db = SQLite3::Database.new( DB_Base::DB_DATA )

db.execute( "select * from artists" ) do |row|
    puts row
end

db.close

class Foo
    def bar(gibberish=nil)
        p gibberish
    rescue
        p 'Ppppffftt!'
    ensure
        p 'done!'
    end
end

foo = Foo.new
foo.bar('stuff')

some_val = nil
if !some_val
    p "nope"
else
    p "yep!"
end

some_val = "y"
some_other_val = "y"
p (some_val == some_other_val)
p "yah baby!" if some_val == some_other_val
p 'this is a ' +
'catenated string'

a = Artist.new()
a.load(1)
puts a.to_s

-----------------

Here is the Artist class in artist.rb:

require 'sqlite3'
require 'db_base'

class Artist
    #   Define our class constants here.  Class constants are
    #   immutable variables accessible by every instance of this
    #   class.

    QRY_SELECT = 'select form, category, media, mediasupport,' +
                 'topic, comments from artists were id = ?'

    QRY_INSERT = 'insert into artists(form, category, media,' +
                 'mediasupport, topic, comments) ' +
                 'values(?, ?, ?, ?, ?, ?)'

    QRY_UPDATE = 'update artists set form = ?, category = ?, ' +
                 'media = ?, mediasupport = ?, topic = ?, comments = ? ' +
                 'where id = ?'

    QRY_DELETE = 'delete from artists where id = ?'

    #   These are our accessors.  They define our
    #   class data and their visibility.  In this
    #   case we are declaring the ability of these
    #   items to be read.

    attr_reader   :id, :form, :category, :media
    attr_reader   :media_support, :topic, :comments
    attr_accessor :dirty, :added

    #   Only the class itself can reference these.

    protected :dirty, :added

    #   Our constructor takes all arguments.  It also
    #   determines whether or not this item is new or
    #   existing.

    def initialize(id=nil, form=nil, category=nil, media=nil,
                   media_support=nil, topic=nil, comments=nil)
        @dirty = false
        @added = false

        @form = form
        @category = category
        @media = media
        @media_support = media_support
        @topic = topic
        @comments = comments

        @added = true if !id
    end

    #   We manually program our writers (class values)
    #   because we need to check whether or not our values
    #   have actually changed.  If they do, we mark our
    #   class object as "dirty".

    def id=(id)
        @dirty = true if id != @id
        @id = id
    end

    def form=(form)
        @dirty = true if form != @form
        @form = form
    end

    def category=(category)
        @dirty = true if category != @category
        @category = category
    end

    def media=(media)
        @dirty = true if media != @media
        @media = media
    end

    def media_support=(media_support)
        @dirty = true if media_support != @media_support
        @media_support = media_support
    end

    def topic=(topic)
        @dirty = true if topic != @topic
        @topic = topic
    end

    def comments=(comments)
        @dirty = true if comments != @comments
        @comments = comments
    end

    #   The rest of these are our methods for loading,
    #   saving and clearing out our object.

    def load(id)
        db = SQLite3::Database.new(DB_Base::DB_DATA)
        db.execute(QRY_SELECT, id) do |row|
            @form = row[0]
            @category = row[1]
            @media = row[2]
            @media_support = row[3]
            @topic = row[4]
            @comments = row[5]
        end
        @id = id
        @dirty = false
        @added = false
        db.close
    end

    def store
        if @dirty or @added
            db = SQLite3::Database.new(DB_Base::DB_DATA)

            if @added
                db.execute(QRY_INSERT,
                           @form, @category, @media, @media_support,
                           @topic, @comments )
                @id = db.last_insert_row_id
                @added = false
            elsif @dirty
                db.execute(QRY_UPDATE,
                           @form, @category, @media, @media_support,
                           @topic, @comments, @id )
                @dirty = false
            end
        end
    ensure
        db.close unless db.closed?
    end

    def kill
        db = SQLite3::Database.new(DB_Base::DB_DATA)
        db.execute(QRY_DELETE, @id)
    ensure
        db.close unless db.closed?
    end

    def to_s
        "Form : #{@form}\nMedia: #{@media}/#{@media_support}"
    end
end

-----------------

This is db_base.rb...

module DB_Base
    #   Base database info.  Keeps constants that identify
    #   our databases.

    DB_DATA = '/Library/Application Support/ArtManager/ArtManager.db'
    DB_IMAGES = '/Library/Application Support/ArtManager/Images.db'
end