A presentation given in early 2011 at Ruby on Rails Oceania about a conceptual refactoring of legacy code written to handle a reality that didn't eventuate.

1. Refactoring Legacy
Code
Learnings from RedBubble
Paul Coia

3. What is Legacy Code?
Untested code
Dead code
Large classes/methods
Spaghetti architecture
Models too rigid to meet new
requirements

4. Product model

5. Available Option
Value
Product Type
Enumeration table
Product
Artwork
OptionOption Value
Print Size,
Frame Colour,
Matte Colour,
Frame Style
Small,
Medium,
Large,
Red,
etc.
FramedPrint

6. Enumeration table
Easy to add new products or options
 No new columns, just insert rows
No code changes
Can query against it
 “Find all artworks available on red t-shirts”
Populate web form elements easily

7. Domain model is in the DB
Product class is a generic type
What about domain logic?
„Instances‟ need a separate set of
tables

8. Buying a product
OptionOption Value
Available Option
Value
Product
Artwork
Product Type
Selected
Product
Selected
Option Value

9. Preparing the product form
framed_print = ProductType.find_by_name(“FramedPrint”)
# Get the Framed Print product
fp_product = artwork.products.detect do |p|
p.product_type == framed_print
end
aovs = fp_product.available_option_values
# Group these into the options
options_hash = {}
aovs.each do |aov|
options_hash[aov.option_value.option] << aov.option_value
end
# Order the option values, so we have S, M, L, etc.
# Populate form elements

10. SQL view
1. Load products by artwork_id
2. Load available_product_options by
product_id
3. Load option_values by option_value_id
4. Load options by option_id

11. Troublesome requirements
Some products have default
options
T-Shirt default colour and style
Options that are not constrained
Calendar start month
Inter-option constraints
Longsleeve Tee colours

12. Default options
Flag on available_product_option
Need to enforce one default per
option type
Render artwork with default
options

13. Rendering default options

14. Rendering the defaults
# Get the default product
tee_product = artwork.get_default_product
aovs = tee_product.available_option_values
defaults = aovs.select {|aov| aov.default? }
# Group these into the options (assuming one per option)
options_hash = {}
defaults.each do |aov|
options_hash[aov.option_value.option] << aov.option_value
end
# Need to validate that we have all required defaults
# and only one per option, etc.

15. SQL view
1. Load products by product_id
2. Load available_product_options by
product_id
3. Load option_values by option_value_id
4. Load options by option_id
 Same joins as the first example

16. Rendering lots of products!

17. Data volumes
0
50
100
150
200
250
300
350
Works Products Available Option Values
Millions

18. Inter option constraints
Roundneck T-shirts can have all
colours
V-Neck can only have a few
How do you model that in the DB?
Do you want to?

19. Original driver
Want to add new products weekly
Really?
Real-world constraints
Product preparation takes months
Cannot cover all eventualities
New products always required new
code anyway

20. Alternative approach
Model product types as classes
Define options and constraints (DSL)
Available products is a list of keys
on Artwork
Available product options is a hash
on the Artwork
So is the default options

21. Product class
class TShirtProduct
option Style, "mens", "T-Shirt"
option Style, "vneck", "V-Neck T-Shirt"
option Style, "longsleeve", "Long Sleeve T-Shirt"
option Style, "womens", "Girly Fitted T-Shirt"
option Style, "mhoodie", "Hoodie"
option Size, "xs", "XS"
option Size, "small", "Small"
option Size, "medium", "Medium”
...
AVAILABLE_COLORS = {
"mens" => all_colors,
"vneck" => [”black”, ”grey”, "navy", "white”]
}
end

22. Database model
Artwork

23. What have we gained?
An expressive, flexible product
model
Simpler code, overall
Actually easier to add products now
And easier to modify existing ones
Nearly 25% average speed increase

24. What have we lost?
“Find all red t-shirts”
Utilise a search engine
“How many large framed prints
have we sold?”
Reporting via Data Warehouse
Online product addition
100s of millions of rows from the DB!