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Rails Active Record Scrapbook

Solve duplicate entries that should be uniq entries

let say we want to detect all rails models that has non uniq entries that suppose to be uniq


Rails.application.eager_load!

ActiveRecord::Base
  .descendants
  .select {|f| f.attribute_names.include?("url_slug") }
  .each do |model|
    p model.to_s
    res = ActiveRecord::Base
      .connection
      .execute("SELECT url_slug FROM #{model.table_name} GROUP BY
url_slug HAVING COUNT(url_slug) > 1;")
    scope = model.where(url_slug: res.to_a.map { |h|
h.fetch("url_slug") })

    begin
      scope = scope.with_deleted   # if the model is using act_as_paranoid / paranoia gem
    rescue NoMethodError
    end

    p scope.count
    p "\n"
  end

rails concerns

require 'active_support/concern'

module Foo
  extend ActiveSupport::Concern
  included do
    def self.method_injected_by_foo
      ...
    end
  end
end

module Bar
  extend ActiveSupport::Concern
  include Foo

  included do
    self.method_injected_by_foo
  end
end

class Host
  include Bar # It works, now Bar takes care of its dependencies
end

http://api.rubyonrails.org/classes/ActiveSupport/Concern.html

get the Active record (rails) db configuration

ActiveRecord::Base.connection.instance_variable_get(:@config)

order via Arel table

class User < ActiveRecord::Base
  has_many :status_changes

  def latest_status_change
    status_changes
     .order(StatusChange.arel_table['created_at'].desc) #
     .first
  end
end

class StatusChange < ActiverRecord::Base
  belongs_to :user
end

resulting in:

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

Benefits:

  • 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

http://apidock.com/rails/ActiveRecord/QueryMethods/order

none

# two are the same thing
tld.validation_types.templates.select { |vt| vt.fields.count == 0  }.empty?
tld.validation_types.none? { |vt| vt.fields.count == 0 }

validations

:name, presence: true, uniqueness: { case_sensitive: true }

validates :in_stock,
  inclusion: { in: [true, false] },
  allow_nil: true  # there is also allow_blank: true

validates :in_stock,
  exclusion: { in: [nil] },
  on: :create  # on create means only when creating resource

validates :email, format: { with: /\ A([ ^@\ s] +)@((?:[-a-z0-9] +\.) +[a-z]{ 2,})\ Z/ i }

validates_length_of :essay,
  minimum: 100,
  too_short: 'Your essay must be at least 100 words.',
  tokenizer: ->(str) { str.scan(/\w+/) } # Specifies how to split up the
             # attribute string. (e.g. tokenizer: ->(str) { str.scan(/\w+/) } to count
             # words). Defaults to ->(value) { value.split(//) }
             # which counts individual characters.

disable readonly on scope

any record loaded via join loaded will be readonly (piggy back object)

class FieldValue < ActiveRecord::Base
  default_scope { joins(:field).readonly(false).merge(Field.positioned) }
end

this will ensure tha when you call Whatever.field_values.create(foo: 'bar) the reccord is writable

ways to set attributes

user.assign_attributes( { foo: 'bar' } )

has one examples

as_one :credit_card, dependent: :destroy  # destroys the associated credit card
has_one :credit_card, dependent: :nullify  # updates the associated records foreign
                                              # key value to NULL rather than destroying it
has_one :last_comment, -> { order 'posted_on' }, class_name: "Comment"
has_one :project_manager, -> { where role: 'project_manager' }, class_name: "Person"
has_one :attachment, as: :attachable
has_one :boss, readonly: :true
has_one :club, through: :membership
has_one :primary_address, -> { where primary: true }, through: :addressables, source: :addressable

source:

PostgreSQL select duplicates only

class Application < ActiveRecord::Base
  scope :have_duplicates, -> { where 'domain in (SELECT domain FROM applications GROUP BY domain HAVING COUNT(domain) > 1)' }
end

Directly execute sql

ActiveRecord::Base.establish_connection
ActiveRecord::Base.connection.execute('select * from ...')

directly on model

MyModel.find_by_sql('select * from') 

skip rails callbacks

Document.skip_callback(:save, :after, :generate_guid)
Document.set_callback(:save, :after, :generate_guid)

Rails empty scope

Validation.none
=> #<ActiveRecord::Relation []> 

oposite to 
Validation.all
=> #<ActiveRecord::Relation [#<Validation id: 1,.....

Joins, Includes and Eager Loading

Eager loading is responsible for prefetching data in one sql query

Product.order("name").includes(:category)

Product.joins(:category, :reviews)
Product.joins(:category, :reviews => :user)
Product.joins("left outer join categories on category_id = categories.id")

products = Product
  .order("categories.name")
  .joins(:categories)
  .select("products.*, categories.name AS category_name")
products.last.category_name

Fetching one column name from association

# app/models/user.rb
def client_name
  read_attribute("client_name") || client.name
end
u = User.order("clients.name").joins(:client).select('users.*, clients.name as client_name')
# => SELECT users.*, clients.name FROM `users` INNER JOIN `clients` ON `clients`.`id` = `users`.`client_id` WHERE (`users`.`deleted_at` IS NULL)
u.client_name

sources

Rails: 3.2.13

Scopes and Arel tricks

scope :visible, where("hidden != ?", true)
scope :published, lambda { where("published_at <= ?", Time.zone.now) }
scope :recent, visible.published.order("published_at desc")
scope :desc_order, order(created_at: :desc)

#bad
has_one :custom_form, -> { order('created_at DESC') }, class_name: CustomForm
# SELECT ORDER BY created_at DESC LIMIT 

#good
has_one :custom_form, -> { order(created_at: :desc) }, class_name: CustomForm
# SELECT .... ORDER BY "custom_forms"."created_at" DESC LIMIT 1

** merging diferent model scopes **

class DocumentVersion
  scope :order_by_latest, ->{ order("document_versions.id DESC") } 
end

class Document
  scope :order_by_latest, ->{ joins(:document_versions).merge(DocumentVersion.order_by_latest) }
end

Document.order_by_latest 

** Multiple or Arel scope**

scope :with_owner_ids_or_global, lambda{ |owner_class, *ids|
  with_ids = where(owner_id: ids.flatten).where_values.reduce(:and)
  with_glob = where(owner_id: nil).where_values.reduce(:and)
  where(owner_type: owner_class.model_name).where(with_ids.or( with_glob ))
}

complex scope example

class Document
  scope :with_latest_super_owner, lambda{ |o|
    raise "must be client or user instance" unless [User, Client].include?(o.class)
    joins(:document_versions, document_creator: :document_creator_ownerships).
    where(document_creator_ownerships: {owner_type: o.class.model_name, owner_id: o.id}).
    where(document_versions: {latest: true}).group('documents.id')
  }
end
# it can get kinda complex :)

Multiple or with bracket separation

# app/model/candy.rb
class Candy < ActiveRecord::Base
  has_many :candy_ownerships
  has_many :clients, through: :candy_ownerships, source: :owner, source_type: 'Client'
  has_many :users,   through: :candy_ownerships, source: :owner, source_type: 'User'

  # ....
  scope :for_user_or_global, ->(user) do
    worldwide_candies  = where(type: 'WorldwideCandies').where_values.reduce(:and)
    client_candies     = where(type: 'ClientCandies', candy_ownerships: { owner_id: user.client.id, owner_type: 'Client'}).where_values.reduce(:and)
    user_candies       = where(type: 'UserCandies',   candy_ownerships: { owner_id: user.id,        owner_type: 'User'  }).where_values.reduce(:and)

    joins(:candy_ownerships).where( worldwide_candies.or( arel_table.grouping(client_candies) ).or( arel_table.grouping(user_candies) ) )
  end

  # ....
end
Candy.for_user_or_global(User.last)
#=> SELECT `candies`.* FROM `candies` INNER JOIN `candy_ownerships` ON `candy_ownerships`.`candy_id` = `candies`.`id` WHERE (`candies`.`deleted_at` IS NULL) AND (((`candies`.`type` = 'WorldwideCandies' OR (`candies`.`type` = 'ClientCandies' AND `candy_ownerships`.`owner_id` = 19 AND `candy_ownerships`.`owner_type` = 'Client')) OR (`candies`.`type` = 'UserCandies' AND `candy_ownerships`.`owner_id` = 121 AND `candy_ownerships`.`owner_type` = 'User')))

Arel lower than

Event.arel_table[:start_at].lt(Time.now).to_sql
=> "`events`.`start_at` < '2013-03-05 10:38:22'" 

Arel give me records that have empty / no associations

# give me all users which has no permissions
User.joins('FULL OUTER JOIN permissions on permissions.user_id = users.id').where(permissions: {user_id:nil})

Arel not equal where statement

DocumentVersion.where( DocumentVersion.arel_table[:id].not_eq(11) )

Arel IS NOT NULL

Foo.includes(:bar).where(Bar.arel_table[:id].not_eq(nil))

# non-arel example:
Foo.where('publication_id IS NOT NULL')

Select Clients that have more that have existing documents

class Client < ActiveRecord::Base
  has_many :documents
  scope :with_existing_documents, ->{ Client.joins(:documents).where(Document.arel_table[:client_id].eq( Client.arel_table[:id]) ).uniq }
end
class Document < ActiveRecord::Base
  belongs_to :client
end

however when you think about it Client.joins(:documents).uniq already do that job by it's own

 # ...
 scope :with_existing_documents, ->{ Client.joins(:documents).uniq }
 #...

so

doc = Document.create
client_without  = Client.create
client_with_doc = Client.create( documents: [doc]
Client.with_existing_documents
# => [client_with_doc]

Sources:

Rails 3.2.13

Updating attributes, columns, and touching stuff

  • update_attribute skips validations, but will touch updated_at and execute callbacks.

  • update_column skips validations, does not touch updated_at, and does not execute callbacks.

so if you want to update column without triggering anything do use update_column, good example is writing your own touch method

def my_touch   
  update_column :cache_changed_at, send(:current_time_from_proper_timezone)
end

if you need to touch field with time

# out of the box touch will run with validations
touch(:cache_changed_at)  #watch out this will update `updated_at` as well

UPDATE `documents` SET `updated_at` = '2013-08-20 11:46:28', `cache_canged_at` = '2013-08-20 11:46:28' WHERE `documents`.`id` = 10

with no args touch will touch updated_at

source : http://stackoverflow.com/a/10824249/473040, http://apidock.com/rails/ActiveRecord/Timestamp/touch

how to detect if column exist in Rails ActiveRecord

Columns are automaticly transformed into methods for instances of thot Model. That mean you can do

event = Event.last
event.respond_to?(:updated_at)
# true

There may be an issues if you writing Rails engine because if model have method with same name, it will return true even if column doesn't exist

So more acurate way is to ask like this:

 event = Event.last
 event['updated_at'].present?  # => true 

This is directly asking instance "what is the value of a column".

If you don't want to trigger sql query to fetch the value of a column but you rather ask model class directly if the column exist you can do this:

 Event.column_names.include?('updated_at')