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January 28, 2016
0 thanks

the method to make 'day' disappear.

If you wanna show “year” and “month” only, you can use “order” to do it:

select_date(Date.current, order: [:year, :month])

That’s it.

January 22, 2016
3 thanks

Creates record by given attributes only if table is empty

This method first searches the table for ANY FIRST RECORD, not the one matching given attributes. If no record is found at all, it creates one using the specified attributes. This might be misunderstood in many cases.

January 22, 2016
0 thanks


When Errno::EEXIST is raised, it indicates there are permission issues, rather than an existing item.

January 6, 2016
0 thanks

What about Marshal remote code execution risks?

Good suggestion about using Marshal to avoid cycles, astgtciv, but what about the security risks of doing that?

See http://ruby-doc.org/core-2.2.2/Marshal.html where it states:

By design, ::load can deserialize almost any class loaded into the Ruby process. In many cases this can lead to remote code
execution if the Marshal data is loaded from an untrusted source.

As a result, ::load is not suitable as a general purpose serialization format and you should never unmarshal user supplied input or other
untrusted data.

If you need to deserialize untrusted data, use JSON or another serialization format that is only able to load simple,primitive’ types such
as String, Array, Hash, etc. Never allow user input to specify arbitrary types to deserialize into.
January 4, 2016 - (>= v1_9_3_392)
0 thanks

Also implemented by other classes

It’s worth noting that this method is also implemented by other classes like Proc, Range and even String.

Most of these are missing proper examples, but you can find some useful examples here:


January 3, 2016
0 thanks


If your integration test is checking for correct behavior of a redirect to the request referer, you can set the referring path in the headers hash with syntax like:

patch update_user_role_path, { user: {role: "vip"} }, { 'HTTP_REFERER' => user_url } 
assert_redirected_to user_url
December 2, 2015
0 thanks

Not quite opposite of new_record?

new_record? will not check if the record has been destroyed

December 2, 2015
1 thank

Not quite opposite of persisted?

persisted? will also check if the record has not been destroyed

November 23, 2015 - (v3.2.13)
0 thanks

Rails 3.2.19

As Jebin reported, we are not getting the value in array format when we set the hidden_field_tag with an Array variable, instead it is a String that we are getting.

November 17, 2015
0 thanks

Find and Detech are the same

@rubynooby: #find and #detect are aliases of the same underlying method. You can use them interchangeably to provide additional readability to your code (find an element to use it or detect if an element is present to do something).


November 13, 2015 - (v1_9_3_125 - v1_9_3_392)
0 thanks

What you really want is

The official Ruby documentation is available for this here http://ruby-doc.org/stdlib-2.2.3/libdoc/rss/rdoc/RSS.html

But the library that will be most helpful to you is called Feedjira: http://feedjira.com/

November 10, 2015
0 thanks

instead of memoize

See this for deprecated github.com/rails/rails/commit/36253916b0b788d6ded56669d37c96ed05c92c5c


def something
  return @_var if defined? @_var
  # more code
November 3, 2015
1 thank

Re: close but no bananna

Actually, @tarasevich is right on this. Let’s have a look at your own example:

[["1","2"],["3","4"]].flat_map {|i| i[0] }     # => ["1", "3"]

[["1","2"],["3","4"]].map {|i| i[0] }.flatten  # => ["1", "3"]
[["1","2"],["3","4"]].flatten.map {|i| i[0] }  # => ["1", "2", "3", "4"]

You are right that both #map and #flatten are non-commutative, it does matter which method is called first.

But #flat_map is equivalent to mapping first and then concatenating (flatten) the results, even if the name might suggest the opposite.

To correctly interpret the method name, you should think of it mathematically as a function composition.

November 3, 2015 - (>= v1_9_2_180)
0 thanks

close but no bananna

@tarasevich noted that

a.flat_map(&b) works exactly like a.map(&b).flatten!(1)

This is backwards because map and flatten are not always interchangeable in order. Mapping over the example array only gives you 2 items. This can result in significant differences depending on what you’re doing in the map. This is easier to demonstrate if we change the example to strings.

[["1","2"],["3","4"]].map {|i| i[0] } # => ["1", "3"]
[["1","2"],["3","4"]].map {|i| i[0] }.flatten  # => ["1", "3"]

BUT if you swap the order

[["1","2"],["3","4"]].flatten.map {|i| i[0] } # => ["1", "2", "3", "4"]

in order to remember what it is equivalent to just note that the method name is already in the correct order. flat_map -> flatten + map

November 3, 2015 - (v4.2.1)
0 thanks

Possible bug

Works as expected for non bang methods

>  a={x:1, y:2, z:3}                                                                      
=> {:x=>1, :y=>2, :z=>3}

> a.slice(:y)                                                                             
=> {:y=>2}

> a.except(:y)                                                                            
=> {:x=>1, :z=>3}

Bug on slice! it behaves like except!

> a.clone.slice!(:y)                                                                                                                                                                                
=> {:x=>1, :z=>3}

> a.clone.except!(:y)                                                                                                                                                                               
=> {:x=>1, :z=>3}

slice! should return {:y=>2} and modify a to no longer have it

October 19, 2015
0 thanks

Multiple files

To use multiple file upload need to use variable_name[].

like this:

file_field_tag 'files[]', :multiple => true  

and in controller:

if !params[ :files ].nil?
  params[ :files ].each{ |file|
     # do your staff
October 13, 2015 - (>= v4.1.8)
0 thanks

"Class methods on your model are automatically available on scopes."

The final example above – “Class methods on your model are automatically available on scopes.” – contains a subtle but vital change from earlier versions of the doc – namely, “pluck” (current example) vs “map” (old example). The former works, the latter does not. See http://github.com/rails/rails/issues/21943 for confirmation that the old documentation is incorrect, and for a workaround.

(Spoiler alert: Use


instead of just


in order to achieve the same effect.)

October 13, 2015 - (>= v4.1.8)
0 thanks

"Class methods on your model are automatically available on scopes."

The final example above – “Class methods on your model are automatically available on scopes.” – does not work as written. See http://github.com/rails/rails/issues/21943 for confirmation that the old documentation is incorrect, and for a workaround.

(Spoiler alert: Use


instead of just


in order to achieve the same effect.)

October 5, 2015 - (>= v3.2.1)
0 thanks

arel_table order by

More objected way how to achieve ORDOR BY .… DESC is like this :

class User < ActiveRecord::Base
  has_many :status_changes

  def latest_status_change

class StatusChange < ActiverRecord::Base
  belongs_to :user

resulting in:

SELECT "status_changes".* FROM "status_changes" WHERE "status_changes"."user_id" = 1 ORDER BY "status_changes"."created_at" DESC


  • you are strictly bound to Modelclass name => renaming table in model will not break the sql code (of if it will, it will explicitly break the syntax on Ruby level, not DB level)

  • you still have the benefit of explicitly saying what table.column the order should be

  • easier to re-factor parts to Query Objects

September 14, 2015 - (v1_9_1_378 - v1_9_3_392)
0 thanks

Getting the return value from the underlying method of an Enumerator

This is documented in the example code, but easy to miss.

When you get an Enumerator using #to_enum(:method_name, …), you can get all of the yielded values using #next, but not the value that is finally returned.

That value can be retrieved via the #result attribute of the StopIteration exception object that is raised when calling #next after the underlying method has returned.

September 9, 2015
1 thank

Warning: prevents persistence but doesn't prevent setting

For example:

class Widget < ActiveRecord::Base
  attr_readonly :key
w = Widget.create! key: 'foo'
w.update! key: 'bar'
w.key #=> 'bar'
w.reload.key #=> 'foo'
September 8, 2015
1 thank

Favicon generator

Hello, I suggest you to try this favicon generator and creator, http://onlinefavicon.com/ , you can create favicon using drawing tool or add picture jpg or other file and make 16x16 or 32x32 ICO file, also see the gallery with favicons from other users or download the same, at end you can read description how to set up favicon to your site!

August 25, 2015
0 thanks

Using Arel

You can also use Arel.

For example:

class ArticlePage < ActiveRecord::Base
  belongs_to :article
  scope :published, -> { where.not(published_at: nil) }
  scope :all_ready, -> { select("every(workflow_state = 'ready') AS is_ready") }

class Article < ActiveRecord::Base
  has_many :article_pages
  def all_ready?
    ActiveRecord::Base.select_values(article_pages.all_ready,published) = 't'
August 18, 2015
0 thanks

Add method to instacne eval

We can add method to instance by using instance_eval.

Code example

string = "String"
string.instance_eval do
  def new_method


irb(main):033:0> string.new_method
=> "gnirtS"
August 3, 2015
1 thank

define_method with default parameters

To define a method with a default parameter the usual notation can be used:

define_method("example") do |fixed, default = {}|
  # something
August 2, 2015
0 thanks

Skip validation

update_all : skip validations, and will save the object to the database regardless of its validity. They should be used with caution.

July 31, 2015
0 thanks

Also takes a block

You can define methods within a block

User = Struct.new(:first_name, :last_name) do
  def full_name
    "#{first_name} #{last_name}"

user = User.new('Simon', 'Templar') # => #<struct User first_name="Simon", last_name="Templar">
user.full_name # => "Simon Templar"
July 16, 2015
0 thanks

I would just use a validation instead of (the probably removed) :required

Just make sure you validate the presence of the association and not the foreign key, otherwise it will not work on new records.

The down side is that it will require the record in the cache, and will make a query otherwise. You can add `unless: :<foreign_key>?` If that’s a problem for you.

July 16, 2015
1 thank

Is :required still valid ?

I get this error when using :required => true

ArgumentError: Unknown key: :required. Valid keys are: :class_name, :class, :foreign_key, :validate, :autosave, :remote, :dependent, :primary_key, :inverse_of, :foreign_type, :polymorphic, :touch, :counter_cache

Is :required not a valid key anymore ?