inopinatus

class Post
  has_many :comments
  has_one :latest_comment, -> { latest_by :post_id }, class_name: 'Comment'

class Comment
  scope :latest_by, -> column {
    from(
      order(column, created_at: :desc).arel
        .distinct_on(arel_table[column])
        .as(quoted_table_name))

inopinatus

scope :search_uid, ->(*terms) {
  where(arel_attribute(:uid).matches_any(terms.map {|term| "%#{sanitize_sql_like term}%" }, nil, true))
}

inopinatus

# frozen_string_literal: true

module CallbackRegistrationTracing
  module Capture
    def normalize_callback_params(*args)
      super.tap do |_, _, options|
        options[:_caller] = caller(3)
      end
    end
  end

inopinatus

# frozen_string_literal: true

# In this example we have an application concerned about the length of a string,
# and is pushing the work to the database for efficiency.  There is an index
# on the length of a Post's title, and the scopes and orderings have been 
# neatly refactored to minimise the amount of Arel required.
#
# A bug has now arisen in the behaviour of `last`.  It is giving the first.
#
# Subsequent investigation has shown that customers were also complaining that

inopinatus

# frozen_string_literal: true

class WorkAllocation
  # Runtime process allocations. Last reviewed: 24/9/2019

  # Half a gig system allocation for agents and monitors and, unfortunately,
  # a couple of deploy-time asset compiles due to dependencies.  It's
  # okay to push some processes into swap on smaller instances during
  # deploy.   Ideally we wouldn't compile on-instance at all.
  OPS_MEMORY_ALLOWANCE = 512

inopinatus

# app/models/concerns/exceeding.rb
module Exceeding
  extend ActiveSupport::Concern

  included do
    scope :exceeds, ->(association, n) do
      joins(association).group(primary_key).having(arel_table[primary_key].count.gteq n)
    end
  end
end

inopinatus

# app/lib/adderall.rb
module Adderall
  def adderall(column_name, relation = self, filter = :itself)
    owner = proxy_association.owner
    records = proxy_association.target

    if loaded? || owner.new_record?
      relation = none
    else
      records = records.select(&:new_record?)

inopinatus

Inequality	Interval	Ruby range	Active Record*	Arel**
n >= x	[x..∞)	x..	where(n: x..)	n.gteq(x)
n <= x	(-∞..x]	..x	where(n: ..x)	n.lteq(x)
n < x	(-∞..x)	...x	where(n: ...x)	n.lt(x)
n > x	(x..∞)	n/a	where.not(n: ..x)	n.gt(x)
x <= n <= y	[x..y]	x..y	where(n: x..y)	n.between(x..y)
x <= n < y	[x..y)	x...y	where(n: x...y)	n.between(x...y)
x < n <= y	(x..y]	n/a	where.not(n: ..x).where(n: ..y)	n.gt(x).and(n.lteq(y))
x < n < y	(x..y)	n/a	where.not(n: ..x).where(n: ...y)	n.gt(x).and(n.lt(y))

inopinatus

module ByMost
  extend ActiveSupport::Concern

  included do
    scope :by_most, ->(assoc) {
      reflection = reflect_on_association(assoc)
      left_joins(assoc)
        .group(primary_key)
        .order(reflection.klass.arel_table[reflection.foreign_key].count.desc)
    }

inopinatus

module DigestQueries
  def predicate_builder
    @predicate_builder ||= super.tap do |pb|
      pb.register_handler(Digest::Instance, DigestHandler.new(pb))
    end
  end

  class DigestHandler
    def initialize(predicate_builder)
      @predicate_builder = predicate_builder