Ruby On Rails Pitfalls

Ruby on Rails Pitfall Or just stupid mistakes we made Robin Lu IN-SRC Studio robinlu@in-src.com RubyConfChina2009

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

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

‘and’ or ‘&&’What does this mean? result = func(arg) and render(:text => result)Why not this? result = func(arg) && render(:text => result)

‘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

strip_tags Display user input text without tagsWhat we did:

strip_tagsWhen text = ‘<img title="http://example.com/x.js?" src="#"’the page becomes:<p> <img title="http://example.com/x.js?" src="#" </p>

strip_tagsstrip_tags is not safe by itself h strip_tags(text)

cacheclass Blog1Controller < ApplicationController def list unless read_fragment(:action => list) @articles = Article.ﬁnd_recent Controller end endend<% cache do %> <ul> <% for article in @articles -%> <li><p><%= h(article.body) %></p></li> list.html.erb <% end -%> </ul><% end %>

cacheResult: sometime got crash due to uninitialized @articles

cachearticle list

cache article listcheck cache

cache article listcheck cache list

cache article listcheck cache list render

cache article list article newcheck cache list render

cache article list article newcheck cache list expire cache render

cache article list article newcheck cache list expire cache rendercheck cache

cache article list article new check cache list expire cache render check cachecrashed by non-init @articles

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

object id

object idCheck nil? everywhere?

object idconﬁg.whiny_nil = true

validate_uniqueness_of

validate_uniqueness_ofWe always get errors like this:A ActiveRecord::StatementInvalid occurred infund#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)

validate_uniqueness_of Process A Process B

validate_uniqueness_of Process A Process B unique?

validate_uniqueness_of Process A Process B unique? select ....

validate_uniqueness_of Process A Process B unique? select .... unique?

validate_uniqueness_of Process A Process B unique? select .... unique? Insert

validate_uniqueness_of Process A Process B unique? select .... unique? Insert Insert

validate_uniqueness_of Process A Process B unique? select .... unique? Insert Insert crash!

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

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

conditionsWhat 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}}

conditionsResult: we get all posts when a category has no subcategories

conditionsWhen category has no subcategorynamed_scope :in_category, lambda { |cat| conditions = [cat.subcategories.map {|subcat| posts.subcategory_id = ? }.join(" OR ")] cat.subcategories.each {|subcat| conditions << subcat.id } {:conditions => conditions}}

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

before_create set a ﬂag if the author of the post is an adminWhat we did:

before_createResult: Only post by admin can be saved

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

after_create send a mail whenever a new record is createdWhat we did:

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

after_create before_create begin ... create ... commit after_createall in one transaction all the steps between this should be transactional

after_createWhat are non-transactional actions?• send a mail• delete a ﬁle• expire a cache

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

Thanks!

Ruby On Rails Pitfalls

by Robin Lu on Mar 27, 2011

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Ruby On Rails Pitfalls — Presentation Transcript