Date Parity

Date formatting and parsing per request in Rails with parity between date.to_s.and string.to_date. Provides a seamless mechanism for allowing custom date format per request, implemented similar to Time.zone.

Rails has great Date formatting and parsing options available. But, it requires a lot of helping code to consistently parse and display dates in a particular format per request. Rails makes this easy for Time.zone parsing, but Date parsing generally requires additional manual parsing code. For example, Date.DATE_FORMATS makes it easy to configure and reuse common formats for your application. But, other then the :default it require an explicit field.to_s(:format) to be applied. More importantly, nothing automatically happens when parsing those dates back from user edits.

Rails also provides the ability to localize your Date formats. But, that requires decisions made for all users in a particular locale.

Often, we need to allow users, companies, organizations, etc. the ability to choose preferred date formats. Both of the Rails standard approaches using Date.DATE_FORMATS or localization fall short at making that easy; especially when parsing user form posted date strings. You end up writing a lot helpers around date fields, and code to normalize posted date values. This generally require explicit steps per field in your model or controller to manually parse; i.e. Date.strptime("1/15/2013", "%m/%d/%Y")

This is where date_parity helps. It is implemented by setting a Date.format string, similar to a per user Time.zone in Rails. This can be set per request (i.e. per user) in a controller's before_action or around_action.

For example:

Date.format = "%m/%d/%Y"
date = "12/31/2012".to_date
=> Mon, 31 Dec 2012
date.to_s
=> "12/31/2012"

Date.format = "%d/%m/%Y"
date = "31/12/2012".to_date
=> Mon, 31 Dec 2012
date.to_s
=> "31/12/2012"

Date.format = '%Y-%m-%d'
date = "2012-12-31".to_date
=> Mon, 31 Dec 2012
date.to_s
=> "2012-12-31"

Date.format = '%d.%m.%Y'
date = "31.12.2012".to_date
=> Mon, 31 Dec 2012
date.to_s
=> "31.12.2012"

Date.format = '%Y.%m.%d'
date = "2012.12.31".to_date
=> Mon, 31 Dec 2012
date.to_s
=> "2012.12.31"

Date.format = '%Y/%m/%d'
date = "2012/12/31".to_date
=> Mon, 31 Dec 2012
date.to_s
=> "2012/12/31"

Installation

Date Parity >= 0.1.0 works with Rails 4.0 onwards. Date Parity 0.0.3 works with Rails 3.

Add this line to your application's Gemfile:

gem 'date_parity'

And then execute:

$ bundle

Or install it yourself as:

$ gem install date_parity

Usage

In a Rails controller before_action: Date.format = '%m/%d/%Y'

Generally, you will want to set that string based on user preference, as in: Date.format = current_user.date_format

Then in any view assuming @model_started_on is a date field, and Date.format was set as above to '%m/%d/%Y':

<%=@modele.started_on  %>
#=> '12/31/2012' 

And then you get parity when a form with this field is posted. Rails will attempt to convert the posted string value of "12/31/2012" using Date.\parse, which DateParity overrides and respects your Date.format.

Without the date_parity gem, @model.start_on would have ended up nil because "12/31/2012" is an invalid argument for ruby Date.parse. However, when date_parity is included, Date will use the format string set on Date.format to correctly parse "12/31/2012", as December 31, 2012, when Date.format = "%m/%d/%Y".

Note: Rails text_field form helper uses @model.attribute_before_type_cast by default. When using date_parity on plain text fields, you will probably want to set your value to explicitly use @model.attribute if it exists. Otherwise, you won't see the formatted date field: For example:

<%= f.text_field :start_on, :value => @user.started_on ||  @user.started_on_before_type_cast %>

Date.format can be set to any date format that can be parsed by strptime. For example, the following are all valid:

Date.format = "%m/%d/%Y"
Date.format = "%d/%m/%Y"
Date.format = '%Y-%m-%d'
Date.format = '%d.%m.%Y'
Date.format = '%Y.%m.%d'
Date.format = '%Y/%m/%d'

Contributing

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Added some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request