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May 23, 2015 - (v1_9_3_392)
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Constants

Reading source one can find detailed patterns: github.com/ruby/ruby/blob/ruby_1_9_3/lib/uri/common.rb

May 22, 2015 - (>= v1_8_6_287)
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Not exactly like map {}.flatten

To also give dimension, is about 4.5 times faster then map {}.flatten.

May 18, 2015
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Are those supported versions correct?

It seems like this method was supported in versions prior to 4.0.2.

UPDATE never mind, wish I could delete this comment..

May 12, 2015
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RE: Convert an Array of Arrays to a Hash using inject

Another way to convert an array of arrays to a hash using inject:

array = [['A', 'a'], ['B', 'b'], ['C', 'c']]

hash = array.inject({}) do |memo, values|
  memo.merge!(values.first => values.last)
end

hash
# => {'A' => 'a', 'B' => 'b', 'C' => 'c'}
May 8, 2015 - (>= v4.0.2)
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This doesn't write files

This doesn’t write files, at least not anymore. Since at least rails 4 `Rack::Cache` isn’t included by default. In any case this method only ever set headers on the response.

May 1, 2015
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Very bad documentation

This is terrible documentation. It makes it very hard to understand what the arguments mean.

The signature is

alias_method(p1, p2)

So what do p1 and p2 mean? The description doesn’t refer to them at all, but to new_name and old_name. How are we supposed to know which is which?

And then it gets even worse in the code sample:

alias_method :orig_exit, :exit

From the naming it sounds like the first argument is the original method name.

Documentation is supposed to resolve this kind of confusion, not create it.

April 29, 2015
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Prevent new line character.

To prevent the “\n” character added at the end of each file pass in the “row_sep: nil” option:

[ "some", "array" ].to_csv                 # => "some, array\n"  

[ "some", "array" ].to_csv( row_sep: nil ) # => "some, array"
April 23, 2015
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add index directly

You can add an index now directly on the foreign_key :

t.references(:user, index: true)
April 21, 2015
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RSS feeds in Rails

Fetching RSS feeds in the request/response cycle inside a Rails application is probably not the very best approach, as it will make your application as slow as the server serving RSS feeds. Another option is to do it asynchronously using a worker or a queue, but this can also become quite complex and hard to maintain over time.

Another solution is to use an API like superfeedr.com and its Rails Engine (http://blog.superfeedr.com/consuming-rss-feeds-rails/). All the polling and parsing is done on Superfeedr’s side and your application is notified in realtime as soon as the resources are updated using a webhook pattern.

April 14, 2015
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Deprecation

It still exists but you give it a block instead of creating a method:

<=2.3.8

def before_create
  self.login = self.first_name
end

Now

before_create :set_login

def set_login
  self.login = self.first_name
end
April 8, 2015 - (v3.1.0 - v4.1.8)
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What object_name.method values will result in checked chekboxes.

*It’s intended that method returns an integer and if that integer is above zero, then the checkbox is checked.* - more exactly, that’s how it’s determined whether value will be checked or not:

(`@checked_value` is checked_value, `value` is what object_name.method returns)

def checked?(value)
  case value
  when TrueClass, FalseClass 
    value == !!@checked_value
  when NilClass
    false
  when String
    value == @checked_value
  else
    if value.respond_to?(:include?)
      value.include?(@checked_value)
    else
      value.to_i == @checked_value.to_i
    end
  end
end
April 2, 2015
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Typo

“Acceptable exception types maye be given as optional arguments. If the last argument is a String, it will be used as the error message.”

>

“Acceptable exception types may be given as optional arguments. If the last argument is a String, it will be used as the error message.”

April 1, 2015 - (>= v4.1.8)
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Parent associations are kept

Maybe this information will save you some time: parent associations (i.e. associations with foreign id in current record) are copied. Don’t assume you’ll get a safely editable object.

March 30, 2015
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Passing a block does not behave as expected

When the condition is true, the block is not rendered:

<%= link_to_if true, users_path, {}, {} do %>
  <i class='fa fa-star'></i>
<% end %>

renders:

<a href="/users">/users</a>

But if the condition is false, the block will render:

<%= link_to_if false, users_path, {}, {} do %>
  <i class='fa fa-star'></i>
<% end %>

renders:

<i class='fa fa-star'></i>
March 30, 2015
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If condition is false, options hash is ignored

Here, the class will be ignored:

<%= link_to_if false, 'Home', root_path, class: 'link' %> 
#=> Home
March 26, 2015
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Save yourself a little typing

We often have a form with a select box that selects a model association. So for example to select a colour, when there is an associated Colour model, a select box will typically select :colour_id.

In this case, ActionView automatically humanizes :colour_id to produce “Colour” as the label text.

March 19, 2015
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enumerator and number of lines to read

Example

File.foreach(filename)
  .take(number_of_lines)
  .map do |line|
    # ... stuff ... 
end
March 19, 2015
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Wrong number of arguments (2 for 1)

If you get this error, wrap brackets with parentheses: Post.find_by_sql([“some query”])

March 19, 2015 - (v4.0.2)
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number_field tag does not accept the same options as text_field_tag

number_field_tag does not accept the size or maxlength options; the max option for number_field_tag is used to control the size of the field. According to W3 http://www.w3.org/TR/html-markup/input.number.html , placeholder should be accepted, but I don’t find that this works in the way it works for text_field_tag.

March 18, 2015
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Transactions and Stale ORM Data

Consider the following:

foo = Foo.new
bar = Bar.new

ActiveRecord::Base.transaction do
  foo.save! # succeeds
  bar.save! # failure, validation problem
end

foo.persisted? # true (!)

foo was not permanently stored in the database, but it was transiently saved, and this is reflected in the ActiveRecord model still in memory. But if you try

foo.reload # raises ActiveRecord::RecordNotFound

Don’t let stale data confuse you after using transactions!

Edited to add: This particular example does not succeed in reproducing the issue I encountered, which involved a slightly more complicated set of nested transactions. I haven’t managed to produce a simple test case where stale data remains in the model, but I have definitely experienced it in my app.

March 18, 2015
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Transactions and Stale ORM Data

Consider the following:

ActiveRecord::Base.transaction do
  foo = Foo.new
  foo.save # succeeds

  bar = Bar.new
  bar.save # failure, validation problem
end
March 17, 2015 - (v2.1.0 - v3.2.13)
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March 11, 2015 - (v1_9_3_392)
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equals a.fetch and a.at(1)

a.fetch(1) == a.at(1) #=> true

March 1, 2015
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Not exactly like map {}.flatten

To clarify on the last comment, conceptually it’s the same, but #flat_map will perform better because there is no need to create an intermediate Array

February 24, 2015
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clarification of inputs

split(p1 = v1, p2 = v2)”

in reading the rest of the documentation, i found “p1” and “p2” to be confusing.

I think it should be:

split( pattern, limit )

February 18, 2015
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Not only for strings, but arrays and hashes too

exclude? is defined as !include?, meaning it is the exact opposite of include? . See the source.

This means that it works for Arrays and Hashes too, as well as for Strings.

It works for Arrays:

>> [nil].exclude?(nil)
=> false
>> [nil].include?(nil)
=> true
>> ["lala"].include?(nil)
=> false
>> ["lala"].exclude?(nil)
=> true

And for Hashes:

>> params = {}
=> {}
>> params[:db] = "lol"
=> "lol"
>> params.exclude?(:db)
=> false
>> params.include?(:db)
=> true
>> 
February 12, 2015
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reorder

adding to stevo’s comment that reorder is also usefull when you have default scope in your model. eg: default_scope -> { order(created_at: :desc) }

February 12, 2015
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Example is a Bug!

Why is the example showing the use of the #detect method and not #find? Boggles the mind!

February 11, 2015
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Redirect to subdomain

If you’re looking to redirect to a subdomain you can do things like this:

redirect_to users_url(1, params: {a: :b}, subdomain: 'bob')