4 files changed, 69 insertions, 5 deletions
diff --git a/activemodel/lib/active_model.rb b/activemodel/lib/active_model.rb
index 46d60db756..58fe08cc11 100644
--- a/activemodel/lib/active_model.rb
+++ b/activemodel/lib/active_model.rb
@@ -28,6 +28,7 @@ require 'active_model/version'
 module ActiveModel
   extend ActiveSupport::Autoload
 
+  autoload :AttributeAssignment
   autoload :AttributeMethods
   autoload :BlockValidator, 'active_model/validator'
   autoload :Callbacks
diff --git a/activemodel/lib/active_model/attribute_assignment.rb b/activemodel/lib/active_model/attribute_assignment.rb
new file mode 100644
index 0000000000..356421476c
--- /dev/null
+++ b/activemodel/lib/active_model/attribute_assignment.rb
@@ -0,0 +1,63 @@
+require 'active_support/core_ext/hash/keys'
+
+module ActiveModel
+  module AttributeAssignment
+    include ActiveModel::ForbiddenAttributesProtection
+
+    # Allows you to set all the attributes by passing in a hash of attributes with
+    # keys matching the attribute names.
+    #
+    # If the passed hash responds to <tt>permitted?</tt> method and the return value
+    # of this method is +false+ an <tt>ActiveModel::ForbiddenAttributesError</tt>
+    # exception is raised.
+    #
+    #   class Cat
+    #     include ActiveModel::AttributeAssignment
+    #     attr_accessor :name, :status
+    #   end
+    #
+    #   cat = Cat.new
+    #   cat.assign_attributes(name: "Gorby", status: "yawning")
+    #   cat.name # => 'Gorby'
+    #   cat.status => 'yawning'
+    #   cat.assign_attributes(status: "sleeping")
+    #   cat.name # => 'Gorby'
+    #   cat.status => 'sleeping'
+    def assign_attributes(new_attributes)
+      if !new_attributes.respond_to?(:stringify_keys)
+        raise ArgumentError, "When assigning attributes, you must pass a hash as an argument."
+      end
+      return if new_attributes.blank?
+
+      attributes = new_attributes.stringify_keys
+      _assign_attributes(sanitize_for_mass_assignment(attributes))
+    end
+
+    private
+
+    def _assign_attributes(attributes)
+      attributes.each do |k, v|
+        _assign_attribute(k, v)
+      end
+    end
+
+    def _assign_attribute(k, v)
+      if respond_to?("#{k}=")
+        public_send("#{k}=", v)
+      else
+        raise UnknownAttributeError.new(self, k)
+      end
+    end
+
+    # Raised when unknown attributes are supplied via mass assignment.
+    class UnknownAttributeError < NoMethodError
+      attr_reader :record, :attribute
+
+      def initialize(record, attribute)
+        @record = record
+        @attribute = attribute
+        super("unknown attribute '#{attribute}' for #{@record.class}.")
+      end
+    end
+  end
+end
diff --git a/activemodel/lib/active_model/errors.rb b/activemodel/lib/active_model/errors.rb
index 912448e43c..a809c72ccd 100644
--- a/activemodel/lib/active_model/errors.rb
+++ b/activemodel/lib/active_model/errors.rb
@@ -2,6 +2,7 @@
 
 require 'active_support/core_ext/array/conversions'
 require 'active_support/core_ext/string/inflections'
+require 'active_support/core_ext/object/deep_dup'
 
 module ActiveModel
   # == Active \Model \Errors
@@ -77,7 +78,7 @@ module ActiveModel
 
     def initialize_dup(other) # :nodoc:
       @messages = other.messages.dup
-      @details  = other.details.dup
+      @details  = other.details.deep_dup
       super
     end
 
diff --git a/activemodel/lib/active_model/model.rb b/activemodel/lib/active_model/model.rb
index d51d6ddcc9..dac8d549a7 100644
--- a/activemodel/lib/active_model/model.rb
+++ b/activemodel/lib/active_model/model.rb
@@ -57,6 +57,7 @@ module ActiveModel
   # (see below).
   module Model
     extend ActiveSupport::Concern
+    include ActiveModel::AttributeAssignment
     include ActiveModel::Validations
     include ActiveModel::Conversion
 
@@ -75,10 +76,8 @@ module ActiveModel
     #   person = Person.new(name: 'bob', age: '18')
     #   person.name # => "bob"
     #   person.age  # => "18"
-    def initialize(params={})
-      params.each do |attr, value|
-        self.public_send("#{attr}=", value)
-      end if params
+    def initialize(attributes={})
+      assign_attributes(attributes) if attributes
 
       super()
     end