Ruby On Rails Pitfall

Ruby on Rails Pitfall Or just stupid mistakes we made Robin Lu IN-SRC Studio [email protected] RubyConfChina2009

Friday, May 22, 2009

IN-SRC Studio • http://www.in-src.com • Team behind Caibangzi.com • Full stack Ruby On Rails Development • Projects from Pepboys,Vitality, Healthwise... Friday, May 22, 2009

‘and’ or ‘&&’ What does this mean? result = func(arg) and render(:text => result)

Friday, May 22, 2009

‘and’ or ‘&&’ What does this mean? result = func(arg) and render(:text => result)

Why not this? result = func(arg) && render(:text => result)

Friday, May 22, 2009

‘and’ or ‘&&’ What does this mean? result = func(arg) and render(:text => result)

Why not this? result = func(arg) && render(:text => result)

Be aware of the operator precedence

Friday, May 22, 2009

strip_tags Display user input text without tags

What we did:

Friday, May 22, 2009

strip_tags When text = ‘
the page becomes:

Friday, May 22, 2009

strip_tags strip_tags is not safe by itself h strip_tags(text)

Friday, May 22, 2009

cache class Blog1Controller < ApplicationController def list unless read_fragment(:action => 'list') @articles = Article.find_recent end end end <% cache do %>

<% for article in @articles -%>

• <%= h(article.body) %>

<% end -%>

<% end %> Friday, May 22, 2009

Controller

list.html.erb

cache Result: sometime got crash due to uninitialized @articles

Friday, May 22, 2009

cache article list

Friday, May 22, 2009

cache article list check cache

Friday, May 22, 2009

cache article list check cache

Friday, May 22, 2009

list

cache article list check cache render

Friday, May 22, 2009

list

cache article new

article list check cache render

Friday, May 22, 2009

list

cache article new

article list check cache render

Friday, May 22, 2009

list

expire cache

cache article new

article list check cache render

Friday, May 22, 2009

list

expire cache

cache article new

article list check cache render check cache

Friday, May 22, 2009

list

expire cache

cache article new

article list check cache render check cache crashed by non-init @articles Friday, May 22, 2009

list

expire cache

cache Solutions?

• defensive: handle the exception • postpone init of @articles • update caches instead of expiring them none of them is perfect

Friday, May 22, 2009

object id

Friday, May 22, 2009

object id Check nil? everywhere?

Friday, May 22, 2009

object id config.whiny_nil = true

Friday, May 22, 2009

validate_uniqueness_of

Friday, May 22, 2009

validate_uniqueness_of We always get errors like this: A ActiveRecord::StatementInvalid occurred in fund#add_watch_fund:  Mysql::Error: Duplicate entry '1234-271' for key 2: INSERT INTO `watch_funds` (`account_id`, `position`, `fund_id`, `created_at`) VALUES(1234, 19, 271, '2009-05-06 19:13:50') Friday, May 22, 2009

validate_uniqueness_of Process A Process B

Friday, May 22, 2009

validate_uniqueness_of Process A Process B unique?

Friday, May 22, 2009

validate_uniqueness_of Process A Process B unique?

Friday, May 22, 2009

select ....

validate_uniqueness_of Process A Process B unique?

select .... unique?

Friday, May 22, 2009

validate_uniqueness_of Process A Process B unique?

select .... unique?

Insert

Friday, May 22, 2009

validate_uniqueness_of Process A Process B unique?

select .... unique?

Insert Insert

Friday, May 22, 2009

validate_uniqueness_of Process A Process B unique?

select .... unique?

Insert Insert

crash!

Friday, May 22, 2009

validate_uniqueness_of validate_uniqueness_of may not guarantee the uniqueness use your own lock if the uniqueness is critical to you.

Friday, May 22, 2009

conditions Background:

• category has many subcategories • subcategory has many posts • post belongs to subcategory we need to select all posts in a category.

Friday, May 22, 2009

conditions What we did: named_scope :in_category, lambda { |cat| conditions = [cat.subcategories.map {|subcat| 'posts.subcategory_id = ?' }.join(" OR ")] cat.subcategories.each {|subcat| conditions << subcat.id } {:conditions => conditions} } Friday, May 22, 2009

conditions Result: we get all posts when a category has no subcategories

Friday, May 22, 2009

conditions When category has no subcategory named_scope :in_category, lambda { |cat| conditions = [cat.subcategories.map {|subcat| 'posts.subcategory_id = ?' }.join(" OR ")] cat.subcategories.each {|subcat| conditions << subcat.id } {:conditions => conditions} } Friday, May 22, 2009

conditions When you compose conditions, be aware that sometime nothing to compose means the conditions should match nothing, not the conditions should be empty.

Friday, May 22, 2009

before_create set a flag if the author of the post is an admin

What we did:

Friday, May 22, 2009

before_create Result: Only post by admin can be saved

Friday, May 22, 2009

before_create

All these callbacks are Filters Be careful not to break the filter chain by what you return from the filters!

Friday, May 22, 2009

after_create send a mail whenever a new record is created

What we did:

Friday, May 22, 2009

after_create Result: sometime the record save failed but we still get mail notification

Friday, May 22, 2009

after_create before_create create after_create all in one transaction

Friday, May 22, 2009

begin ... ... commit all the steps between this should be transactional

after_create What are non-transactional actions?

• send a mail • delete a file • expire a cache

Friday, May 22, 2009

after_create • try not put non-transaction actions into transactions.

• after_commit • in controller

Friday, May 22, 2009

Thanks!

Friday, May 22, 2009