MemoryRecord

Introduction

A simple library that handles a few records easily. With this library can flexibly managed immutable data.

Installation

Install as a standalone gem

$ gem install memory_record

Or install within application using Gemfile

$ bundle add memory_record
$ bundle install

Examples

Basic usage 1

class Palette
  include MemoryRecord
  memory_record [
    { key: :coral,  },
    { key: :tomato, },
    { key: :gold,   },
  ]
end

Palette[:tomato].key   # => :tomato
Palette[:tomato].name  # => "tomato"
Palette[:tomato].code  # => 1

Basic usage 2

class Palette
  include MemoryRecord
  memory_record [
    { key: :coral,  r: 255, g: 127, b:   0 },
    { key: :tomato, r: 255, g:  99, b:  71 },
    { key: :gold,   r: 255, g: 215, b:   0 },
  ]
end

Palette[:tomato].key   # => :tomato
Palette[:tomato].name  # => "tomato"
Palette[:tomato].code  # => 1
Palette[:tomato].r     # => 255
Palette[:tomato].g     # => 99
Palette[:tomato].b     # => 71

Basic usage 3

class Palette
  include MemoryRecord
  memory_record [
    { key: :coral,  r: 255, g: 127, b:   0 },
    { key: :tomato, r: 255, g:  99, b:  71 },
    { key: :gold,   r: 255, g: 215, b:   0 },
  ]

  def rgb
    [r, g, b]
  end

  def hex
    "#" + rgb.collect { |e| "%02X" % e }.join
  end

  def name
    super.capitalize
  end
end

Palette[:tomato].key   # => :tomato
Palette[:tomato].name  # => "Tomato"
Palette[:tomato].code  # => 1
Palette[:tomato].rgb   # => [255, 99, 71]
Palette[:tomato].hex   # => "#FF6347"
Palette.collect(&:hex) # => ["#FF7F00", "#FF6347", "#FFD700"]

How to turn as an array?

Enumerable extended, so that each method is available

Palette.each { |e| ... }
Palette.collect { |e| ... }

How do I submit a form to select in Rails?

form.collection_select(:pallet_key, Palette, :key, :name)   // object[pallet_key]=tomato
form.collection_select(:pallet_key, Palette, :code, :name)  // object[pallet_key]=1

Either way can see it with Palette[pallet_key]

Is the reference in subscripts slow?

Since it has a hash internally using the key value as a key, it can be acquired with O (1).

Palette[1].name       # => "Tomato"
Palette[:tomato].name # => "Tomato"

Instances always react to code and key

object = Palette[:tomato]
object.key  # => :tomato
object.code # => 1

How do I add a method to an instance?

For that, I am creating a new class so I need to define it normally

name method is special?

If name is not defined, it defines a name method that returns key.to_s

to_s method is defined?

Alias of name, to_s is defined.

If there is no key, use fetch to get an error

Palette.fetch(:xxx)              # => <KeyError: ...>

The following are all the same

Palette[:xxx] || :default        # => :default
Palette.fetch(:xxx, :default}    # => :default
Palette.fetch(:xxx) { :default } # => :default

Use fetch_if to ignore if the key is nil

Palette.fetch_if(nil)            # => nil
Palette.fetch_if(:tomato)        # => #<Palette:... @attributes={...}>
Palette.fetch_if(:xxx)           # => <KeyError: ...>

Key validation

Palette.valid_key(:tomato)          # => :tomato
Palette.valid_key("tomato")         # => :tomato
Palette.valid_key(1)                # => :tomato
Palette.valid_key(:xxx)             # => nil
Palette.valid_key(:xxx, :tomato)    # => :tomato
Palette.valid_key(:xxx) { :tomato } # => :tomato

Palette.valid_key(:xxx, :tomato)          # => :tomato
Palette.valid_key(:xxx, :black) rescue $! # => #<KeyError: Palette.fetch(:black) does not match anything

A common example in Rails

palette_key = Palette.valid_key(params[:palette_key], :tomato)

How to refer to other keys

class Foo
  include MemoryRecord
  memory_record [
    { key: :a, other_key: :x },
    { key: :b, other_key: :y },
    { key: :c, other_key: :z },
  ]

  class << self
    def lookup(v)
      super || invert_table[v]
    end

    private

    def invert_table
      @invert_table ||= inject({}) {|a, e| a.merge(e.other_key => e) }
    end
  end
end

Foo[:a] == Foo[:x]                  # => true
Foo[:b] == Foo[:y]                  # => true
Foo[:c] == Foo[:z]                  # => true

How prohibit the hash key from being attr_reader automatically?

Use attr_reader: false or attr_reader: {only: ...} or attr_reader: {except: ...}

class Foo
  include MemoryRecord
  memory_record attr_reader: {only: :y} do
    [
      { x: 1, y: 1, z: 1 },
    ]
  end
end

Foo.first.x rescue $! # => #<NoMethodError: undefined method `x' for #<Foo:0x007fcc861ff108>>
Foo.first.y rescue $! # => 1
Foo.first.z rescue $! # => #<NoMethodError: undefined method `z' for #<Foo:0x007fcc861ff108>>

How to decide code yourself?

class Foo
  include MemoryRecord
  memory_record [
    { code: 1, key: :a, name: "A" },
    { code: 2, key: :b, name: "B" },
  ]
end

Foo.collect(&:code) # => [1, 2]

It is not recommended to specify it explicitly. It is useful only when refactoring legacy code with compatibility in mind.

Convert to JSON

Similar to ActiveModel's serialization, there is an only except methods include method.

class ColorInfo
  include MemoryRecord
  memory_record [
    { key: :blue, rgb: [  0, 0, 255], },
    { key: :red,  rgb: [255, 0,   0], },
  ]

  def hex
    "#" + rgb.collect { |e| "%02X" % e }.join
  end

  def children
    [
      {x: 1, y: 2},
      {x: 3, y: 4},
    ]
  end
end

color_info = ColorInfo.first
color_info.as_json                          # => {:key=>:blue, :rgb=>[0, 0, 255], :a=>1, :code=>0}
color_info.as_json(only: :key)              # => {:key => :blue}
color_info.as_json(except: [:rgb, :code])   # => {:key => :blue}
color_info.as_json(only: [], methods: :hex) # => {:hex => "#0000FF"}
color_info.as_json(only: [], include: {children: {only: :x}} ) # => {:children => [{"x" => 1}, {"x" => 3}]}

ColorInfo.as_json(only: :key)               # => [{:key=>:blue}, {:key=>:red}]
ColorInfo.to_json(only: :key)               # => "[{\"key\":\"blue\"},{\"key\":\"red\"}]"

Case of ActiveModelSerializers

class ColorInfoSerializer < ActiveModel::Serializer
  attributes :key
end

ActiveModelSerializers::SerializableResource.new(ColorInfo.first).as_json # => { :key => :blue }