ActiveModel::Errors::Tree

Did you too search Google for a way to encode your Rails errors in your API? Well you probably encountered an awful response like this:

render json: { errors: @record.errors.messages }, status: :unprocessable_entity

This is not a good mechanism.

Why? Let's say you have a model with associations. The way ActiveRecord encodes errors.messages is this:

{ :field => ["can't be blank"], :"association.field" => ["must be less than 5"] }

Let's say you developed a great client side implementation to figure out "association.field" is actually an error on the association model. What happens when it's a one-to-many association?

{ :field => ["can't be blank"], :"associations.field" => ["must be less than 5"] }

What?! How are you supposed to know which instance of associations received the error? How do you mark the correct textbox in red?

Add this line to your application's Gemfile:

gem 'activemodel-errors-tree'

And then execute:

$ bundle

Or install it yourself as:

$ gem install activemodel-errors-tree

By calling @record.errors.tree you get a much prettier picture, that is easier to decode on the client side.

Following the examples above:

@record.errors.tree.messages
# This is actually a ActiveSupport::HashWithIndifferentAccess
=> { field: ["can't be blank"], association: { field: ["must be less than 5"] } }

@record.errors.tree.messages
# Assuming the error is on the second association out of three.
=> { field: ["can't be blank"], associations: [{}, { field: ["must be less than 5"] }, {}] }

Now your client can iterate over the association's errors along with rendering the associations, and render out each association's errors.

If you use Rails 5 or include the active_model-errors_details gem, you can use @record.errors.tree.details instead of messages. This is more API friendly since it let's your client decide on the actual messages.

@record.errors.tree.details
# Assuming the error is on the second association out of three.
=> { field: [{ error: :blank }], associations: [{}, { field: [{ error: :less_than, count: 5 }] }, {}] }

After checking out the repo, run bin/setup to install dependencies. Then, run rake rspec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

Bug reports and pull requests are welcome on GitHub at https://github.com/odedniv/activemodel-errors-tree. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.