Custom error messages for required properties in Hashie::Dash subclasses

CHANGELOG.md

@@ -1,6 +1,7 @@
 ## Next Release
 
 * Your contribution here.
+* [#233](https://github.com/intridea/hashie/pull/233): Custom error messages for required properties in Hashie::Dash subclasses - [@joss](https://github.com/joss).
 * [#231](https://github.com/intridea/hashie/pull/231): Added support for coercion on class type that inherit from Hash - [@gregory](https://github.com/gregory).
 * [#228](https://github.com/intridea/hashie/pull/228): Made Hashie::Extensions::Parsers::YamlErbParser pass template filename to ERB - [@jperville](https://github.com/jperville).
 * [#224](https://github.com/intridea/hashie/pull/224): Merging Hashie::Mash now correctly only calls the block on duplicate values - [@amysutedja](https://github.com/amysutedja).

README.md

@@ -385,22 +385,26 @@ safe_mash.zip = 'Test' # => ArgumentError
 
 ## Dash
 
-Dash is an extended Hash that has a discrete set of defined properties and only those properties may be set on the hash. Additionally, you can set defaults for each property. You can also flag a property as required. Required properties will raise an exception if unset.
+Dash is an extended Hash that has a discrete set of defined properties and only those properties may be set on the hash. Additionally, you can set defaults for each property. You can also flag a property as required. Required properties will raise an exception if unset. Another option is message for required properties, which allow you to add custom messages for required property.
 
 ### Example:
 
 ```ruby
 class Person < Hashie::Dash
   property :name, required: true
+  property :age, required: true, message: 'must be set.'
   property :email
   property :occupation, default: 'Rubyist'
 end
 
 p = Person.new # => ArgumentError: The property 'name' is required for this Dash.
+p = Person.new(name: 'Bob') # => ArgumentError: The property 'age' must be set.
 
-p = Person.new(name: "Bob")
-p.name # => 'Bob'
-p.name = nil # => ArgumentError: The property 'name' is required for this Dash.
+p = Person.new(name: "Bob", age: 18)
+p.name         # => 'Bob'
+p.name = nil   # => ArgumentError: The property 'name' is required for this Dash.
+p.age          # => 18
+p.age = nil    # => ArgumentError: The property 'age' must be set.
 p.email = 'abc@def.com'
 p.occupation   # => 'Rubyist'
 p.email        # => 'abc@def.com'

lib/hashie/dash.rb

@@ -27,6 +27,7 @@ module Hashie
     # * <tt>:required</tt> - Specify the value as required for this
     #   property, to raise an error if a value is unset in a new or
     #   existing Dash.
+    # * <tt>:message</tt> - Specify custom error message for required property
     #
     def self.property(property_name, options = {})
       properties << property_name
@@ -46,7 +47,12 @@ module Hashie
       if defined? @subclasses
         @subclasses.each { |klass| klass.property(property_name, options) }
       end
-      required_properties << property_name if options.delete(:required)
+
+      if options.delete(:required)
+        required_properties[property_name] = options.delete(:message) || "is required for #{name}."
+      else
+        fail ArgumentError, 'The :message option should be used with :required option.' if options.key?(:message)
+      end
     end
 
     class << self
@@ -55,7 +61,7 @@ module Hashie
     end
     instance_variable_set('@properties', Set.new)
     instance_variable_set('@defaults', {})
-    instance_variable_set('@required_properties', Set.new)
+    instance_variable_set('@required_properties', {})
 
     def self.inherited(klass)
       super
@@ -74,7 +80,7 @@ module Hashie
     # Check to see if the specified property is
     # required.
     def self.required?(name)
-      required_properties.include? name
+      required_properties.key? name
     end
 
     # You may initialize a Dash with an attributes hash
@@ -168,7 +174,7 @@ module Hashie
     end
 
     def assert_required_attributes_set!
-      self.class.required_properties.each do |required_property|
+      self.class.required_properties.each_key do |required_property|
         assert_property_set!(required_property)
       end
     end
@@ -182,7 +188,7 @@ module Hashie
     end
 
     def fail_property_required_error!(property)
-      fail ArgumentError, "The property '#{property}' is required for #{self.class.name}."
+      fail ArgumentError, "The property '#{property}' #{self.class.required_properties[property]}"
     end
 
     def fail_no_property_error!(property)

spec/hashie/dash_spec.rb

@@ -34,6 +34,10 @@ class SubclassedTest < DashTest
   property :last_name, required: true
 end
 
+class RequiredMessageTest < DashTest
+  property :first_name, required: true, message: 'must be set.'
+end
+
 class DashDefaultTest < Hashie::Dash
   property :aliases, default: ['Snake']
 end
@@ -47,11 +51,20 @@ describe DashTest do
     [ArgumentError, "The property '#{property}' is required for #{subject.class.name}."]
   end
 
+  def property_required_custom_error(property)
+    [ArgumentError, "The property '#{property}' must be set."]
+  end
+
+  def property_message_without_required_error
+    [ArgumentError, 'The :message option should be used with :required option.']
+  end
+
   def no_property_error(property)
     [NoMethodError, "The property '#{property}' is not defined for #{subject.class.name}."]
   end
 
   subject { DashTest.new(first_name: 'Bob', email: 'bob@example.com') }
+  let(:required_message) { RequiredMessageTest.new(first_name: 'Bob') }
 
   it('subclasses Hashie::Hash') { should respond_to(:to_mash) }
 
@@ -83,13 +96,29 @@ describe DashTest do
     expect { subject.first_name = nil }.to raise_error(*property_required_error('first_name'))
   end
 
+  it 'errors out when message added to not required property' do
+    expect do
+      class DashMessageOptionWithoutRequiredTest < Hashie::Dash
+        property :first_name, message: 'is required.'
+      end
+    end.to raise_error(*property_message_without_required_error)
+
+    expect do
+      class DashMessageOptionWithoutRequiredTest < Hashie::Dash
+        property :first_name, required: false, message: 'is required.'
+      end
+    end.to raise_error(*property_message_without_required_error)
+  end
+
   context 'writing to properties' do
     it 'fails writing a required property to nil' do
       expect { subject.first_name = nil }.to raise_error(*property_required_error('first_name'))
+      expect { required_message.first_name = nil }.to raise_error(*property_required_custom_error('first_name'))
     end
 
     it 'fails writing a required property to nil using []=' do
       expect { subject[:first_name] = nil }.to raise_error(*property_required_error('first_name'))
+      expect { required_message[:first_name] = nil }.to raise_error(*property_required_custom_error('first_name'))
     end
 
     it 'fails writing to a non-existent property using []=' do