rails & ruby

Proc & Lambda

#difference between proc and 

rails.org

Inheritance, Mixins, and Design P81

Liskov Substitution Principle. Formally, this states, “Let q(x) be a property provable about objects x of type T. Then q(y) should be true for objects y of type S where S is a subtype of T.”

keywords differences

• load, require https://prograils.com/posts/ruby-methods-differences-load-require-include-extend require reads and parses files only once, when they were referenced for the first time. load reads and parses files every time you call `load`.
• include, extend include , add methods to class extend , Unlike include, which adds module’s methods as instance methods, extend allows you to add them as a class methods.

  module TestModule
  def some_method
    "Some method of #{self.class}"
  end
  end
  
  class TestClass1
    extend TestModule
  # ...
  end
  class TestClass
    extend TestModule
    # ...
  end
  
  TestClass2.some_method
  TestClass1.new.some_method
      

rvm

*install gem globally rvm @global do gem install [gem_name] to install gem globally (per ruby version). It is not possible to install gem globally for every ruby version. According to https://rvm.io/gemsets/initial you can define automatically installed gems for every ruby version in file ~/.rvm/gemsets/global.gems. In this file you need to define required gems (one per line) e.g. bundler zeus

ruby sql dsl

• integer

  :limit	NumericType	ColumnSize	Maxvalue
  1	tinyint	1 byte	127
  2	smallint	2 bytes	32767
  3	mediumint	3 byte	8388607
  nil, 4, 11	int(11)	4 byte	2147483647
  5..8	bigint	8 byte	9223372036854775807

银行支付

• RSA 加密
  • to_s, to_json, to_json 会把symbol :xx 转换成 “xx”, to_s 不会

    [28] pry(main)> h={
    [28] pry(main)*   name: "hello"
    [28] pry(main)* }
    => {:name=>"hello"}
    [29] pry(main)> h.to_s
    => "{:name=>\"hello\"}"
    [30] pry(main)> h.to_json
    => "{\"name\":\"hello\"}"
            

  • 用到的特殊方法 Array#pack ,#unpack

programming ruby:

• instance method: File#read class method: File.read, constant: File::EOF
• scope :wq

rails

• render and return
• puts “sss” and return false # => nil and 后面的语句要想执行的, 则and的左部分需要返回true

query

• 查询部分字段 User.pluck(:id), 查询某个字段, 直接把数据库中的字段返回成数组,不构建Active Record 对象 User.select(:id).map(&:id), 会构建Active Record 对象
• 检查是否存在 User.exist?(2), # id User.exist(name: ‘Tom’)

  Article.first.categories.any? Article.first.categories.many?

• unscoped 删除所有作用域 User.unscoped.all
• includes ,加载关联 User.includes(:address).all
• 多表查询 Person .select(‘people.id, people.name, companies.name’) .joins(:company) .find_by(‘people.name’ => ‘John’) # this should be the last

active record validate

• Active Record 验证结束后，所有发现的错误都可以通过实例方法 errors.messages 获取， 该方法返回一个错误集合。如果数据验证后，这个集合为空，则说明对象是合法的
• 仅字段存在才验证 allow_blank => true or :if => lambda {|attr| attr.present?}
• 以下方法会跳过 验证

  decrement!
  decrement_counter
  increment!
  increment_counter
  toggle!
  touch
  update_all
  update_attribute
  update_column
  update_columns
  update_counters
      

• 多个字段联合唯一验证 validates_uniqueness_of :phone, :scope => :site_id

create table

 class CreateProducts < ActiveRecord::Migration
 def change
  create_table :products do |t|
    t.string :name
    t.text :description

    t.timestamps
  end
  end
end

支持的属性 limit：设置 string/text/binary/integer 类型字段的最大值； precision：设置 decimal 类型字段的精度，即数字的位数； scale：设置 decimal 类型字段小数点后的数字位数； polymorphic：为 belongs_to 关联添加 type 字段； null：是否允许该字段的值为 NULL；

call back

• 可用的回调 下面列出了所有可用的 Active Record 回调，按照执行各操作时触发的顺序：

  3.1 创建对象 before_validation after_validation before_save around_save before_create around_create after_create after_save 3.2 更新对象 before_validation after_validation before_save around_save before_update around_update after_update after_save 3.3 销毁对象 before_destroy around_destroy after_destroy 3.4 查找对象 after_find after_initialize 其他 after_touch 条件回调

  before_save: :do_some_thing, if: :need_do?
  #use proc
  before_save :normalize_card_number,
   if: Proc.new { |order| order.paid_with_card? }
      

• 跳过回调 decrement decrement_counter delete delete_all increment increment_counter toggle touch update_column update_columns update_all update_counters

puts & p

puts return nil, puts simply string represent of the object p return argument passed, output equal puts object.inspect

array

• arr = [1, 2, 4] start=1, count=2 arr[start, count]

  arr[-1] # last one arr[1..2] # from 1 to 2

  • stack = arr.clone stack.pop # => 4
  • queue = stack.clone queue.shift # => 1

scope

In ActiveRecord, all query building methods (like where, order, joins, limit and so forth) return a so called scope.

• scope with scope scope :recent, -> { where(‘updated_at > ?’, 5.minutes.ago }

  scope :non_admin, -> { without_role :admin }

  scope :non_admin, -> { where(admin: false) } scope :non_admin_recent, -> { non_admin.recent }

• scope with multiple conditions scope :recent, lambda { :conditions > ['updated_at > ? AND admin ! ?’, 5.minutes.ago, true] }