In a JavaScript console, type this:
> 9112347935156469760
9112347935156470000
Ooops. And that's not a float!
This occurs because JavaScript uses double precision floats to store numbers.
So according to IEEE floating point definition only numbers between -(2^53 - 1) (-9007199254740991) and 2^53 - 1 (9007199254740991) can safely be represented in JavaScript.
Note that ECMAScript 6 will probably also offer [Number.MAX_SAFE_INTEGER](https://developer.mozilla.org/en-US/docs/W...
Cookies without an expiration timestamp are called "session cookies". [1] They should only be kept until the end of the browsing session.
However, when Chrome or Firefox are configured to reopen tabs from last time upon start, they will keep session cookies when closing the browser. This even applies to tabs that were closed before shutting down the browser.
This is by design in Chrome and [Firefox](https://bugzilla.mozilla.org/buglist.cgi?bug_id=337551,345830,358042,362212,36...
Capybara will fail to find <a> tags that are missing an href attribute. This will probably happen to you every now and then on JavaScript-heavy applications.
An example would be an AngularJS application where the following HTML actually works. [1]
<a ng-click="hello()">Hello</a>
Capybara will fail to find that link, even though looking it up via the DOM shows it:
>> find_link("Hello")
Capybara::ElementNotFound: Unable to find link "Hello"
>> find("a").text
=> "Hello"
To make find_link and click_link work, ...
Due to network or hardware failures, it can happen that one of your cronjobs will not run at the time you specify in the schedule. Your code should be built in a way that it can be re-run at a later time (when the failure is resolved).
For example, if you are synchronizing data with another service once every day, your cronjob should not only synchronize changes from the last 24 hours. If you do this and a network failure will delay the execution of your job by 5 hours, you will only synchronize changes from hour 6-29, but forget change...
Safari on iOS accepts an apple-touch-icon favicon that is used for stuff like desktop bookmarks. Always define a solid background color for them.
If you use PNGs with a transparent background, Safari will use just set a black background on your pretty icon. This is almost never what you want.
You can fix that by applying a white background via ImageMagick like this:
convert a...
This card describes how to pass an array with multiple element to a JavaScript function, so that the first array element becomes the first function argument, the second element becomes the second argument, etc.
Note how this is different from passing the entire array as the first argument. Compare these two different ways of calling fun() in Ruby:
# Ruby
array = [1, 2, 3]
fun(array) # same as fun([1, 2, 3]) (1 argument)
fun(*array) # same as fun(1, 2, 3) (3 arguments)
Depending on your culture the spreading of array eleme...
When you have a string containing umlauts which don't behave as expected (are not matched with a regexp, can't be found with an SQL query, do not print correctly on LaTeX documents, etc), you may be encountering umlauts which are not actually umlaut characters.
They look, depending on the font, like their "real" umlaut counterpart:
However, they are not the same:
>> 'ä' == 'ä'
=> false
>> 'ä'.size
=> 1
>> 'ä'.size
=> 2
Looking at how those strings are constructed reveals what is going...
Your development machine is usually on a very good network connection.
To test how your application behaves on a slow network (e.g. mobile), you can simulate limited bandwidth.
By default, Rails' validates_uniqueness_of does not consider "username" and "USERNAME" to be a collision. If you use MySQL this will lead to issues, since string comparisons are case-insensitive in MySQL.
(If you use PostgreSQL, read this instead.)
Say you have a user model
class User < ActiveRecord::Base
validates_uniqueness_of :name
end
with a unique index in the database.
If you try to create the users "user" and "USER", this will not trigger a validation error, but may fail with an SQL error due ...
When you call a method on an object, Ruby looks for the implementation of that method. It looks in the following places and uses the first implementation it finds:
Let's say we h...
Tests are about 100% control over UI interaction and your test scenario. Randomness makes writing tests hard. You will also push tests that are green for you today, but red for a colleague tomorrow.
That said, please don't do something like this:
Factory(:document) do |document|
document.category { ['foo', 'bar', 'baz'].sample }
end
Instead do this:
Factory(:document) do |document|
document.category 'foo'
end
I even recommend to not use libraries like [Faker]...
| What | Rails version | Within before_*
|
Within after_*
|
|---|---|---|---|
| Cancel later callbacks | Rails 1-4 | return false |
return false |
| Cancel later callbacks | Rails 5+ | throw :abort |
throw :abort |
| Rollback the transaction | Rails 1-4 | return false |
raise ActiveRecord::Rollback |
| Rollback the transaction | Rails 5+ | `thr... |
Say you have a User with a Carrierwave attribute #avatar:
class User < ActiveRecord::Base
mount_uploader :avatar, AvatarUploader
end
When whitelisting the avatar field in the controller, you might do this:
params[:user].permit(:avatar)
But you probably want this:
params[:user].permit(:avatar, :avatar_cache, :remove_avatar)
In this example:
:avatar_cache allows a newly upload image to persist through form roundtrips in the case of validation errors (something that isn't possibl...Whenever you create a table from a database migration, remember to add updated_at and created_at timestamps to that table. Without those timestamps, investigating future bug reports will be hell. Always have timestamps.
When you create a table using create_table, you can add timestamps by using the timestamps shortcut:
class CreateEpisode < ActiveRecord::Migration
def change
create_table :episodes do |t|
t.string :name
t.timestam...
When two classes implement the same behavior (methods, callbacks, etc.), you should extract that behavior into a trait or module. This card describes how to test that extracted behavior without repeating yourself.
Note that the examples below use Modularity traits to extract shared behavior. This is simply because we like to do it that way at makandra. The same techniques apply for modules and overriding self.included.
Example
---...
Custom matchers are a useful RSpec feature which you can use to DRY up repetitive expectations in your specs. Unfortunately the default directory structure generated by rspec-rails has no obvious place to put custom matchers or other support code.
I recommend storing them like this:
spec/support/database_cleaner.rb
spec/support/devise.rb
spec/support/factory_bot.rb
spec/support/vcr.rb
spec/support/matchers/be_allowed_access.rb
s...
We tend to use database transactions as a magic bullet to get rid of all our concurrency problems. When things get really bad, we might even throw in some locking mechanism, but then are usually done with it.
Unfortunately, transactions semantics in databases are actually very complicated, and chances are, your making some incorrect assumptions.
The MySQL innodb engine actually has [four different modes](ht...
If you save your uploads to a made up directory like "RAILS_ROOT/uploads", this directory goes away after every deploy (since every release gets a new). Also this directory is not shared between multiple application servers, so your uploads are randomly saved to one local filesystem or another. Fixing this afterwards is a lot of fun.
Only two folders are, by default, shared between our application servers and deployments: "RAILS_ROOT/storage" and `"RAILS...
Merge requests are often rejected for similar reasons.
To avoid this, before you send a merge request, please confirm that your code ...
console.log(...), byebug etc.Sometimes you want git to ignore certain files that appear on your machine. You can do this in 3 ways:
.gitignore file.gitignore entriesWhile it might be tempting to set it per project (other devs might benefit from it), you
.gitignore file with stuff...In the following example the method update_offices_people_count won't be called when office_id changes, because it gets overwritten by the second line:
after_save :update_offices_people_count, :if => :office_id_changed? # is overwritten …
after_save :update_offices_people_count, :if => :trashed_changed? # … by this line
Instead write:
after_save :update_offices_people_count, :if => :office_people_count_needs_update?
private
def office_people_count_needs_update?
office_id_changed? || trashed_changed?
end
Or...
Rails gives you migrations to change your database schema with simple commands like add_column or update.
Unfortunately these commands are simply not expressive enough to handle complex cases.
This card outlines three different techniques you can use to describe nontrivial migrations in Rails / ActiveRecord.
Note that the techniques below should serve you well for tables with many thousand rows. Once your database tables grows to millions of rows, migration performance becomes an iss...
Be careful with the Active Record where method. When you accidentally pass an empty array to the where method using NOT IN, you probably will not get what you expected:
User.where("id NOT IN (?)", [])
=> SELECT `users`.* FROM `users` WHERE (id NOT IN (NULL))
Even though you might expect this to return all records, this actually results none.
Never use the expression id NOT IN (?) without taking care of this case! See below some workarounds.
Rails < 4 does not provide a pretty workaround.
ids = ...
Do not pass times to date attributes. Always convert times to dates when your application uses time zones.
A time-zoned Time attribute on a Rails record is converted to UTC using to_s(:db) to be stored, and converted back into the correct time zone when the record is loaded from the database. So when you are not on UTC, time objects will be converted as follows.
>> Time.current
=> Fri, 15 Mar 2013 11:56:03 CET +01:00
>> Time.current.to_s(:db)
=> "2013-03-15 10:56:03" # This is now UTC
That will...