how to change output of a single attribute?

[glaucocustodio]

Hey, thank you for the awesome work on Shale, it's really great.

Since discussions is not enabled on this repo, I am opening a issue to hear from you.

Problem

Imagine we have a very long mapper:

class User < Shale::Mapper
  attribute :first_name, Shale::Type::String
  attribute :last_name, Shale::Type::String
  attribute :gender, Shale::Type::String # gender will come as either 'f' or 'm'
  # many more other attributes...
end

And we would like to change the output of a single attribute (across all formats JSON, YAML, TOML, CSV and XML) so gender returns male instead of m and female instead of f

If I got it right, one would need to define map for all fields across all formats right? Eg:

class User < Shale::Mapper
  attribute :first_name, Shale::Type::String
  attribute :last_name, Shale::Type::String
  attribute :gender, Shale::Type::String # gender will come as either 'f' or 'm'
  # many more other attributes...

  json do
    map "first_name", to: :first_name
    map "last_name", to: :last_name
    # and so on...
    map "gender", using: {from: :gender_from_json, to: :gender_to_json}
  end

  def gender_from_json(model, value)
    model.gender = if value == 'f'
      'female'
    else
      'male'
    end
  end
end

we could also create a custom type, eg:

class CustomGender < Shale::Type::Value
  def self.cast(value)
    if value == "m"
      "male"
    else
      "female"
    end
  end
end

class User < Shale::Mapper
  attribute :first_name, Shale::Type::String
  attribute :last_name, Shale::Type::String
  attribute :gender, CustomGender
  # many more other attributes...
end

Using custom type seems less worse, but it still feels way too verbose..

Proposed solution #1

Would you be happy if we could override a single method instead of defining mappings for all attributes? Eg:

class User < Shale::Mapper
  attribute :first_name, Shale::Type::String
  attribute :last_name, Shale::Type::String
  attribute :gender, Shale::Type::String

  # change output of gender for all formats: json, xml etc
  def gender(model, value)
    model.gender = if value == 'f'
      'female'
    else
      'male'
    end
  end
end

Proposed solution #2

In case you are not happy with #1, what about defining a method to be called when reading a single attribute? Eg:

class User < Shale::Mapper
  attribute :first_name, Shale::Type::String
  attribute :last_name, Shale::Type::String
  attribute :gender, Shale::Type::String, read_with: :verbose_gender

  def verbose_gender(model, value)
    model.gender = if value == 'f'
      'female'
    else
      'male'
    end
  end
end

Please let me know if there is an easier way to accomplish the thing or if you would accept a PR implementing either of the proposed solutions.

[kgiszczak]

hey, you can achieve that using just plain Ruby, no need for special constructs:

class User < Shale::Mapper
  attribute :gender, Shale::Type::String

  def gender
    if super == 'f'
      'female'
    else
      'male'
    end
  end
end

although this behavior is confusing, the JSON doc you generate will be different then the one you're consuming (unless that's what you specifically need):

puts User.from_json('{"gender":"m"}').to_json
# => {"gender":"male"}

The proper way to solve this imo is to use custom type:

class Gender < Shale::Type::Value
  def self.of_json(value, **)
    value == 'm' ? 'male' : 'female'
  end

  def self.as_json(value, **)
    value == 'male' ? 'm' : 'f'
  end
end

class User < Shale::Mapper
  attribute :gender, Gender
end

This works as you would expect:

user = User.from_json('{"gender":"m"}')

puts user.gender
# => male

puts user.to_json
# => {"gender":"m"}

[glaucocustodio]

Since I'm only parsing a json and not to converting to it back, I am gonna override the method like you showed:

class User < Shale::Mapper
  attribute :gender, Shale::Type::String

  def gender
    if super == 'f'
      'female'
    else
      'male'
    end
  end
end

Would you accept a PR describing this behaviour with its caveat on README?

[kgiszczak]

having that in README would be a great addition, PR is welcome