JenniferTwin

Super simple library to dump/load Jennifer model attributes to plain class instance to be able to integrate it with any kind of hidden attributes.

Installation

1. Add the dependency to your shard.yml:

dependencies:
  jennifer_twin:
    github: imdrasil/jennifer_twin
    version: 0.1.1

2. Run shards install

Usage

Jennifer generates some amount of hidden attributes for a mode to be able to track whether attribute has been changed, relation load state or just a collection, etc. For some tasks you would like to have an instance containing only model attributes or it's subset. One of the most popular example - JSON::Serializable. Therefor JenniferTwin copies all data from original instance and store them.

If you trying to solve issue of model serialization to JSON - take a look at Serializer.

To create a twin include JenniferTwin and call .map_fields macro:

require "jennifer_twin"

class UserTwin
  include JenniferTwin

  map_fields User
end

Mapping

.map_fields macro generates only 3 things:

• getters for all fields named after model's ones (unless other name is specified)
• initializer accepting model instance to copy
• #to_model method to create a model instance from it's fields

user = User.all.first
user_twin = UserTwin.new(user)
user_twin.to_model # => User

As a 2nd argument macro accepts named tuple or symbol-based hash of field options. Supported options are:

• :ignore - if set to true ignores specified field
• :key - defines attribute with the specified value
• :annotations - adds annotations above field setter

Let's take a look at more descriptive example:

class User < Jennifer::Model::Base
  mapping(
    id: Primary32,
    name: String?,
    age: Int32?,
    password_hash: String?
  )
end

class UserTwin
  include JenniferTwin
  include JSON::Serializable

  map_fields(User, {
    age: { annotations: [@[JSON::Field(emit_null: true)]] }
    name: { key: :full_name },
    password_hash: { ignore: true }
  })

  setter full_name
end

user = User.all.first # <User:0x000000000010 id: 1, name: "User 8", age: nil, password_hash: "<hash>">
user_twin = UserTwin.new(user) # <UserTwin:0x000000000020 @id=1, @full_name="User 8", @age=nil>
user_twin.to_json # => %({"id":1,"full_name":"User 8","age":null})

user_twin.full_name = "New Name"
user_twin.to_modal # <User:0x000000000030 id: nil, name: "New Name", age: nil, password_hash: nil>

Also you can add additional custom logic to generated initializer passing a block to the macro call. To access model instance use record variable name.

class UserTwin
  include JenniferTwin

  getter full_name : String

  map_fields(User) do
    @full_name = "#{record.name} Snow"
  end
end

Contributing

1. Fork it (https://github.com/imdrasil/jennifer_twin/fork)
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create a new Pull Request

Contributors

• Roman Kalnytskyi - creator and maintainer