Implement initialize_with to allow overriding object instantiation

Factory Girl now allows factories to override object instantiation. This
means factories can use factory methods (e.g. methods other than new) as
well as pass arguments explicitly.

    factory :user do
      ignore do
        things { ["thing 1", "thing 2"] }
      end

      initialize_with { User.construct_with_things(things) }
    end

    factory :report_generator do
      ignore do
        name { "Generic Report" }
        data { {:foo => "bar", :baz => "buzz"} }
      end

      initialize_with { ReportGenerator.new(name, data) }
    end

Whitespace

Code recommendations

GETTING_STARTED.md

@@ -590,6 +590,42 @@ To set the attributes for each of the factories, you can pass in a hash as you n
 twenty_year_olds = FactoryGirl.build_list(:user, 25, :date_of_birth => 20.years.ago)
 ```
 
+Custom Construction
+-------------------
+
+Instantiating objects can be overridden in the case where you'd rather not
+call `new` on your build class or you have some other factory method that
+you'd prefer to use. Using custom construction also allows for your objects to
+be instantiated with any number of arguments.
+
+```ruby
+# user.rb
+class User
+  attr_accessor :name, :email
+
+  def initialize(name)
+    @name = name
+  end
+end
+
+# factories.rb
+sequence(:name) {|n| "person#{n}@example.com" }
+
+factory :user do
+  ignore do
+    name { Faker::Name.name }
+  end
+
+  email
+  initialize_with { User.new(name) }
+end
+
+FactoryGirl.build(:user).name # Bob Hope
+```
+
+Notice that I ignored the `name` attribute. If you don't want attributes
+reassigned after your object has been instantiated, you'll want to `ignore` them.
+
 Cucumber Integration
 --------------------
 
@@ -620,4 +656,4 @@ User.blueprint do
 end
 
 User.make(:name => 'Johnny')
-```
+```

lib/factory_girl/attribute_assigner.rb

@@ -1,7 +1,7 @@
 module FactoryGirl
   class AttributeAssigner
-    def initialize(build_class, evaluator)
-      @build_class              = build_class
+    def initialize(evaluator, &instance_builder)
+      @instance_builder         = instance_builder
       @evaluator                = evaluator
       @attribute_list           = evaluator.class.attribute_list
       @attribute_names_assigned = []
@@ -29,7 +29,7 @@ module FactoryGirl
     private
 
     def build_class_instance
-      @build_class_instance ||= @build_class.new
+      @build_class_instance ||= @evaluator.instance_exec(&@instance_builder)
     end
 
     def get(attribute_name)

lib/factory_girl/definition.rb

@@ -1,6 +1,6 @@
 module FactoryGirl
   class Definition
-    attr_reader :callbacks, :defined_traits, :declarations
+    attr_reader :callbacks, :defined_traits, :declarations, :constructor
 
     def initialize(name = nil, base_traits = [])
       @declarations      = DeclarationList.new(name)
@@ -9,6 +9,7 @@ module FactoryGirl
       @to_create         = lambda {|instance| instance.save! }
       @base_traits       = base_traits
       @additional_traits = []
+      @constructor       = nil
     end
 
     delegate :declare_attribute, :to => :declarations
@@ -50,6 +51,10 @@ module FactoryGirl
       @defined_traits << trait
     end
 
+    def define_constructor(&block)
+      @constructor = block
+    end
+
     private
 
     def base_traits

lib/factory_girl/definition_proxy.rb

@@ -161,5 +161,9 @@ module FactoryGirl
     def trait(name, &block)
       @definition.define_trait(Trait.new(name, &block))
     end
+
+    def initialize_with(&block)
+      @definition.define_constructor(&block)
+    end
   end
 end

lib/factory_girl/factory.rb

@@ -43,7 +43,7 @@ module FactoryGirl
       proxy = proxy_class.new
 
       evaluator = evaluator_class.new(proxy, overrides.symbolize_keys)
-      attribute_assigner = AttributeAssigner.new(build_class, evaluator)
+      attribute_assigner = AttributeAssigner.new(evaluator, &instance_builder)
 
       proxy.result(attribute_assigner, to_create).tap(&block)
     end
@@ -123,6 +123,10 @@ module FactoryGirl
       processing_order.map {|factory| factory.callbacks }.flatten
     end
 
+    def constructor
+      @constructor ||= @definition.constructor || parent.constructor
+    end
+
     private
 
     def assert_valid_options(options)
@@ -143,6 +147,11 @@ module FactoryGirl
       end
     end
 
+    def instance_builder
+      build_class = self.build_class
+      constructor || lambda { build_class.new }
+    end
+
     def initialize_copy(source)
       super
       @definition = @definition.clone

lib/factory_girl/null_factory.rb

@@ -6,7 +6,7 @@ module FactoryGirl
       @definition = Definition.new
     end
 
-    delegate :defined_traits, :callbacks, :attributes, :to => :definition
+    delegate :defined_traits, :callbacks, :attributes, :constructor, :to => :definition
 
     def compile; end
     def class_name; end

spec/acceptance/initialize_with_spec.rb

@@ -0,0 +1,147 @@
+require "spec_helper"
+
+describe "initialize_with with non-FG attributes" do
+  include FactoryGirl::Syntax::Methods
+
+  before do
+    define_model("User", :name => :string, :age => :integer) do
+      def self.construct(name, age)
+        new(:name => name, :age => age)
+      end
+    end
+
+    FactoryGirl.define do
+      factory :user do
+        initialize_with { User.construct("John Doe", 21) }
+      end
+    end
+  end
+
+  subject    { build(:user) }
+  its(:name) { should == "John Doe" }
+  its(:age)  { should == 21 }
+end
+
+describe "initialize_with with FG attributes that are ignored" do
+  include FactoryGirl::Syntax::Methods
+
+  before do
+    define_model("User", :name => :string) do
+      def self.construct(name)
+        new(:name => "#{name} from .construct")
+      end
+    end
+
+    FactoryGirl.define do
+      factory :user do
+        ignore do
+          name { "Handsome Chap" }
+        end
+
+        initialize_with { User.construct(name) }
+      end
+    end
+  end
+
+  subject    { build(:user) }
+  its(:name) { should == "Handsome Chap from .construct" }
+end
+
+describe "initialize_with with FG attributes that are not ignored" do
+  include FactoryGirl::Syntax::Methods
+
+  before do
+    define_model("User", :name => :string) do
+      def self.construct(name)
+        new(:name => "#{name} from .construct")
+      end
+    end
+
+    FactoryGirl.define do
+      factory :user do
+        name { "Handsome Chap" }
+
+        initialize_with { User.construct(name) }
+      end
+    end
+  end
+
+  it "assigns each attribute even if the attribute has been used in the constructor" do
+    build(:user).name.should == "Handsome Chap"
+  end
+end
+
+describe "initialize_with non-ORM-backed objects" do
+  include FactoryGirl::Syntax::Methods
+
+  before do
+    define_class("ReportGenerator") do
+      attr_reader :name, :data
+
+      def initialize(name, data)
+        @name = name
+        @data = data
+      end
+    end
+
+    FactoryGirl.define do
+      sequence(:random_data) { 5.times.map { Kernel.rand(200) } }
+
+      factory :report_generator do
+        ignore do
+          name "My Awesome Report"
+        end
+
+        initialize_with { ReportGenerator.new(name, FactoryGirl.generate(:random_data)) }
+      end
+    end
+  end
+
+  it "allows for overrides" do
+    build(:report_generator, :name => "Overridden").name.should == "Overridden"
+  end
+
+  it "generates random data" do
+    build(:report_generator).data.length.should == 5
+  end
+end
+
+describe "initialize_with parent and child factories" do
+  before do
+    define_class("Awesome") do
+      attr_reader :name
+
+      def initialize(name)
+        @name = name
+      end
+    end
+
+    FactoryGirl.define do
+      factory :awesome do
+        ignore do
+          name "Great"
+        end
+
+        initialize_with { Awesome.new(name) }
+
+        factory :sub_awesome do
+          ignore do
+            name "Sub"
+          end
+        end
+
+        factory :super_awesome do
+          initialize_with { Awesome.new("Super") }
+        end
+      end
+    end
+  end
+
+  it "uses the parent's constructor when the child factory doesn't assign it" do
+    FactoryGirl.build(:sub_awesome).name.should == "Sub"
+  end
+
+  it "allows child factories to override initialize_with" do
+    FactoryGirl.build(:super_awesome).name.should == "Super"
+  end
+end

spec/factory_girl/definition_proxy_spec.rb

@@ -184,3 +184,14 @@ describe FactoryGirl::DefinitionProxy, "#trait" do
     subject.should have_trait(:male).with_block(male_trait)
   end
 end
+
+describe FactoryGirl::DefinitionProxy, "#initialize_with" do
+  subject     { FactoryGirl::Definition.new }
+  let(:proxy) { FactoryGirl::DefinitionProxy.new(subject) }
+
+  it "defines the constructor on the definition" do
+    constructor = Proc.new { Array.new }
+    proxy.initialize_with(&constructor)
+    subject.constructor.should == constructor
+  end
+end

spec/factory_girl/null_factory_spec.rb

@@ -4,6 +4,7 @@ describe FactoryGirl::NullFactory do
   it { should delegate(:defined_traits).to(:definition) }
   it { should delegate(:callbacks).to(:definition) }
   it { should delegate(:attributes).to(:definition) }
+  it { should delegate(:constructor).to(:definition) }
 
   its(:compile)          { should be_nil }
   its(:class_name)       { should be_nil }