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December 6, 2013
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Migration for uniqueness with existent data in DB

I’m using sub-transaction to update existent records on DB. I use this approach to update the uniqueness field when it value dependent on another existent field without uniqueness restriction.

Migration for uniqueness with existent dependent data in DB

class AddUniquenessBarToFoo < ActiveRecord::Migration
  class Foo < ActiveRecord::Base

  def change

    add_column :foos, :bar, :string
    execute "ALTER TABLE foos ADD CONSTRAINT uk_foods_bar UNIQUE (bar)"    

    Foo.all.each do |f|
        #try get unique value in a new sub-transaction
        Foo.transaction(requires_new: true) do
          f.update_attributes!(:bar => "some ops. with another non-unique existent field to set this")
      rescue ActiveRecord::StatementInvalid
         #We can't reuse a crashed transaction. New one.
         Foo.transaction(requires_new: true) do
          #Alternative unique value, if another error exist it's another
          #migration problem and then raise new error.
          f.update_attributes!(:bar => "some operation to set this-#{f.id}")
    change_column :foos, :bar, :string, :null => false


Be aware about performance that is transaction per record for big DB.

December 3, 2013
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usage examples

For detailed usage examples of where see “Conditions” under ActiveRecord::Base.

December 2, 2013 - (v3.2.13)
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Redirect Status

Redirect 302

get "/accounts", :to => redirect("/", :status => 302)
November 26, 2013
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Updated list of statuses

The list of supported statuses is now in the layout & rendering rails guide:


November 22, 2013
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November 19, 2013
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Return value not correct

It seems like trap returns nil if the handler was “DEFAULT”, but calling trap with nil causes a “IGNORE”

2.0.0-p247 :020 > p trap("CHLD", "DEFAULT")
 => nil 
2.0.0-p247 :021 > p trap("CHLD", nil)
 => nil 

So it seems that once you trap a signal, there isn’t a way to reset them back to what they were originally.

November 18, 2013
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BEWARE of options[:value] in a partial

No problem with new records however,

the following line will not display the current @ecard value on EDIT but ‘contact@host.com’.

text_field :ecard, :sender, :value => 'contact@host.com'

Don’t let your views take control, but if you insist:

text_field :ecard, :sender, :value => f.object.ecard.blank? ? 'contact@host.com' : f.object.ecard

This doesn’t make sense, since when this object was created they deleted the default, which made it blank. Why would they want it back?

November 15, 2013
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Test if an array is included in another

a note for anoiaque solution…

before running you need to require set

require 'set'
class Array
  def included_in? array

[1,2,4].included_in?([1,10,2,34,4]) #=> true
November 13, 2013 - (v3.2.13)
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Just for completeness (it should behave like this), comparing ranges that start and end with the same value will overlap, e.g.

(1..5).overlaps?(5..10) # => true
November 13, 2013 - (v3.2.13)
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Take care with time ranges

Trying this in the console:


will blow up…

It’s fine with Dates though:

(1.day.from_now.to_date..5.days.from_now.to_date).overlaps?(5.days.from_now.to_date..10.days.from_now.to_date) # => true
November 12, 2013
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Be aware

Be aware

'John    Doe №88'.sqeeze 
=> 'John Doe №8' # with just one '8'
November 8, 2013
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submit button with rails javascript's onclick event handler method

Code example

<%= f.submit ‘Create User’, class: ‘buttons’, :onclick => “validate_user_form_and_submit()” %>

November 7, 2013
1 thank


Where you see:

HelperData.new(datetime, options, html_options).select_hour

The correct would be:

HelperDate.new(datetime, options, html_options).select_hour

Class name and class instance must be same name.

Code works fine in Rails 3.2.13.

November 5, 2013
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The "instance-level equivalent" ActiveRecord::Base#increment is NOT atomic

Typically, you want to increment counters atomically, so the class method ActiveRecord::Base.increment_counter is the right choice.

Also, there is an issue with the increment example below as it does not save automatically:

item = Item.find(1)
item.foo_count # => 0
item.foo_count # => 1
item.foo_count # => 0
item.foo_count # => 1
October 21, 2013 - (v2.3.8)
1 thank

Found out you can't set the type to number

I am sure others have tried to do this but I thought I would add a not that tells ever one. You can’t use the type field in in rails 2.3. It is always set back to type => “text”

So if you are trying to set it to type => “number” it will not work. It always goes back to text. Sorry only way around this is to use a text_field_tag and set the type in that.

<%= text_field_tag :thing, type: "number" %>

Code above is the only way to set the type. in rails 3 you can just call number_field and it will work

October 16, 2013
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Erb tags

The <% -%> is not being used since Rails 3.

The example above should be changed to:

<%= form_tag('/posts') do %>
  <div><%= submit_tag 'Save' %></div>
<% end %>
October 11, 2013 - (<= v3.2.13)
1 thank

Bug - this is not working as documented

The stacking of several after_commit lines is not working. The last line overwrites the ones before.

Using an array for the :on options is also not working.

For details look here: http://github.com/rails/rails/issues/988#issuecomment-12653474

October 10, 2013
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Classy guys...

:fav_bra_size - really?

October 2, 2013
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You have explain well

You have explain well about fragment caching as I was in need of this information. http://autobodycarparts.com

October 2, 2013
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Thanks for the coding part it was really helpful for me, I would apply it on my project. http://www.koolchart.com

October 1, 2013
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Update multiple attributes with raw sql

You can update multiple attributes with sql for each record being updated by using the following syntax:


Model.update_all("foo = 'bar', baz = 'bat'")
September 27, 2013
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Using find_index to return first match. Profit!

This example shows how to use find_index to return a result as soon as the first occurrence of what you are looking for is found.

Code example

class Widget < Struct.new(:name, :profit); end

class WidgetManager
  def initialize(*widgets)
    @widgets = widgets
  def is_any_widget_profitable?
    @widgets.find_index { |w| w.profit > 0 }  # <== usage!

wm = WidgetManager.new(Widget.new('a', -100), Widget.new('b', 200), Widget.new('c', 300))
wm.is_any_widget_profitable?  # => 1
(wm.is_any_widget_profitable?) ? 'some profit' : 'all loss'  # => "some profit"

wm = WidgetManager.new(Widget.new('a', -100), Widget.new('b', -200), Widget.new('c', -300))
wm.is_any_widget_profitable?  # => nil
(wm.is_any_widget_profitable?) ? 'some profit' : 'all loss'  # => "all loss"
September 25, 2013
0 thanks

Anothery way

This Worked For Me

require File.expand_path('../app/models/extenstions/active_record_ext', File.dirname(__FILE__))

I did this in application.rb

September 24, 2013
0 thanks

Missing documentation for options hash

The deprecated function (http://apidock.com/rails/ActiveRecord/Serialization/to_json) has more useful documentation for the options hash.

September 13, 2013
0 thanks

Edge case

NilClass#try doesn’t check for methods on itself:

nil.blank?        #=> true
nil.try :blank?   #=> nil
September 11, 2013 - (v3.2.13)
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touch in rails

touch is used to update the updated_at column you can create a model instance and update the updated_at value on it

Let say we have one user model

user = User.first

next you can write


so it will run the query for you

UPDATE `users` SET `updated_at` = ‘current_date_time’ WHERE `users`.`id` = 1

Alternatively, to update some other column with the current date and time use:


September 9, 2013
1 thank

Using reject to remove key/value pairs from a hash

Code example

# Remove empty strings
{ a: 'first', b: '', c: 'third' }.reject { |k,v| v.empty? } #=> {:a=>"first", :c=>"third"}

# Remove nil
{a: 'first', b: nil, c: 'third'}.reject { |k,v| v.nil? } # => {:a=>"first", :c=>"third"}

# Remove nil & empty strings
{a: '', b: nil, c: 'third'}.reject { |k,v| v.nil? || v.empty? } # => {:c=>"third"}
September 8, 2013
0 thanks

without a bang

We can use hash#slice if we want an Hash#extract (without bang) like behavior.

August 24, 2013
1 thank

expires_in option

@concept47 do you really need to check the fragment in the controller?

ActiveRecord will execute the query when its used

cars = Car.where(:colour => 'black') # No Query
cars.each {|c| puts c.name } # Fires "select * from cars where ..."

“Lazy Loading” - http://m.onkey.org/active-record-query-interface