Rails: Mapping a Date from form parameters into ActiveModel object - ruby-on-rails

Question

I have a filter-class which includes ActiveModel and consists of two dates:
class MealFilter
include ActiveModel::Model
attribute :day_from, Date
attribute :day_to, Date
end
That model is rendered into a form as following:
<%= form_for(#filter) do |f| %>
<div class="form-group form-group--date">
<%= f.label :day_from %>
<%= f.date_select :day_from %>
</div>
<div class="form-group form-group--date">
<%= f.label :day_to %>
<%= f.date_select :day_to %>
</div>
<% end %>
The problem is now, when the form gets submitted, it sends this parameters to the controller:
{"utf8"=>"✓", "meal_filter"=>{"day_from(1i)"=>"2016", "day_from(2i)"=>"1", "day_from(3i)"=>"29", "day_to(1i)"=>"2016", "day_to(2i)"=>"1", "day_to(3i)"=>"30"}, "commit"=>"Filter"}
I extract the values via Controller parameters:
def meal_filter_params
if params.has_key? :meal_filter
params.require(:meal_filter).permit(:day_from, :day_to)
end
end
if I now assign the params[:meal_filter] to my MealFilter class with #filter = MealFilter.new(meal_filter_params), my date fields are not updated correctly. It seams that the 1i, 2i, 3i parts are not correctly assigned to the dates.
However, this works fine if used an ActiveRecord class.
Do I miss some include? Does anyone know, where this magic mapping is implemented if not in ActiveModel::Model?

Answer 1

I came across this issue while upgrading an app from Rails 3.2 to 5.0
How I sorted it out is as follows:
For Rails 5
class MealFilter
include ActiveRecord::AttributeAssignment
attr_reader :day_from
def initialize(attributes = {})
self.attributes = attributes || {}
end
def day_from=(value)
#day_from = ActiveRecord::Type::Date.new.cast(value)
end
end
For Rails 4.2
class MealFilter
include ActiveRecord::AttributeAssignment
attr_accessor :day_from
def initialize(attributes = {})
self.attributes = attributes || {}
end
def type_for_attribute(name)
case name
when "day_from" then ActiveRecord::Type::Date.new
end
end
end
Then you can do:
attributes = { "day_from(3i)" => "1", "day_from(2i)" => "9", "day_from(1i)" => "2020" }
meal_filter = MealFilter.new(attributes)
meal_filter.day_from
# => Tue, 01 Sep 2020

Answer 2

Ok, found a solution.
What I needed was the MultiparameterAssignment which is actually implemented in ActiveRecord but not in ActiveModel.
As far as I can see, there is an open pull request (https://github.com/rails/rails/pull/8189) that should resolve this issue.
But in the meantime, some clever guy wrote a module that can be included into the model: https://gist.github.com/mhuggins/6c3d343fd800cf88f28e
All you need to do is to include the concern and define a class_for_attribute method that returns the class where your attribute should be mapped to - in my case Date.

Answer 3

You can simply access the 1i, 2i and 3i parameters from the date_select helper and combine them to make new Date in a before_validation callback:
class DateOfBirth
include ActiveModel::Model
include ActiveModel::Attributes
include ActiveModel::Validations::Callbacks
attribute :date_of_birth, :date
attribute "date_of_birth(3i)", :string
attribute "date_of_birth(2i)", :string
attribute "date_of_birth(1i)", :string
before_validation :make_a_date
validates :date_of_birth, presence: { message: "You need to enter a valid date of birth" }
def make_a_date
year = self.send("date_of_birth(1i)").to_i
month = self.send("date_of_birth(2i)").to_i
day = self.send("date_of_birth(3i)").to_i
begin # catch invalid dates, e.g. 31 Feb
self.date_of_birth = Date.new(year, month, day)
rescue ArgumentError
return
end
end
end