diff --git a/Gemfile b/Gemfile
index 0bdcb12..ec9cdf9 100644
--- a/Gemfile
+++ b/Gemfile
@@ -4,4 +4,4 @@ group :test do
   gem 'rspec_junit_formatter', '0.2.2'
 end
 # Specify your gem's dependencies in static_models.gemspec
-gemspec
+gemspec
\ No newline at end of file
diff --git a/lib/static_models.rb b/lib/static_models.rb
index e3d1de8..b0b0ea7 100644
--- a/lib/static_models.rb
+++ b/lib/static_models.rb
@@ -42,12 +42,24 @@ def valid?
       def self.where(*args)
         all
       end
+
+      def ==(other)
+        other.try(:id) == id
+      end
+
+      def hash
+        "static_model_#{self.class.object_id}_#{id}".freeze.hash
+      end
+
+      def eql?(other)
+        other == self
+      end
     end
 
     class_methods do
       NumberType = if Gem::Version.new(RUBY_VERSION) >= Gem::Version.new('2.4.0')
         Integer
-      else  
+      else
         Fixnum
       end
 
@@ -103,11 +115,11 @@ def static_models_hashes(columns, hashes)
       end
 
       def find(id)
-        values[id.to_i]
+        values[id.to_i] || (raise NotFoundError.new("id #{id} not found"))
       end
 
       def find_by_code(code)
-        all.select{|x| x.code == code.try(:to_sym)}.first 
+        all.select{|x| x.code == code.try(:to_sym)}.first
       end
 
       def all
@@ -144,7 +156,7 @@ def belongs_to(association, opts = {})
         define_method("#{association}") do
           klass = expected_class || send("#{association}_type").to_s.safe_constantize
 
-          if klass && klass.include?(Model)
+          if klass && klass.include?(Model) && send("#{association}_id").present?
             klass.find(send("#{association}_id"))
           elsif defined?(super)
             super()
@@ -180,7 +192,7 @@ def belongs_to(association, opts = {})
             instance_variable_set("@invalid_#{association}_code",
               value.try(:to_sym))
           end
-        end 
+        end
 
         define_method("#{association}_code") do
           send(association).try(:code) ||
@@ -191,4 +203,5 @@ def belongs_to(association, opts = {})
   end
 
   class ValueError < StandardError; end
+  class NotFoundError < StandardError; end
 end
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index 76ef410..05bb44e 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -5,7 +5,6 @@
 require 'byebug'
 require "static_models"
 
-
 # Require our macros and extensions
 Dir[File.expand_path('../../spec/support/macros/**/*.rb', __FILE__)].map(&method(:require))
 
diff --git a/spec/static_models_spec.rb b/spec/static_models_spec.rb
index 21f5339..b8ff1ad 100644
--- a/spec/static_models_spec.rb
+++ b/spec/static_models_spec.rb
@@ -20,7 +20,6 @@ class Dog
 end
 
 describe StaticModels::Model do
-
   it "defines and uses a static model" do
     Breed.corgi.tap do |b|
       b.should == Breed.find(6)
@@ -50,6 +49,23 @@ class Dog
     }
   end
 
+  describe "when comparing equality" do
+    it "is equal when same code is used" do
+      expect(Breed.collie).to eq Breed.new(id: 1, code: :collie, height: nil)
+    end
+    it "can compare inside sets" do
+      expect( Set.new([Breed.collie]))
+        .to eq Set.new([Breed.new(id: 1, code: :collie, height: nil)])
+    end
+    it 'does not fail when compare with anything not a static model' do
+      expect(Breed.collie).not_to eq(true)
+    end
+  end
+
+  it "throws an error when model not found" do
+    expect { Breed.find(56) }.to raise_error(StaticModels::NotFoundError)
+  end
+
   it "has a model name" do
     Breed.model_name.plural.should == "breeds"
   end
@@ -115,13 +131,13 @@ def self.checks_sparse(title, *table)
       check_def("checks sparse "+ title) do static_models_sparse(table) end
     end
 
-    checks_sparse "id is Fixnum", ["hello", :foo]
+    checks_sparse "id is Integer", ["hello", :foo]
     checks_sparse "code is Symbol", [1, 2323]
     checks_sparse "has only id, code, and Hash", [1, :bar, :ble, foo: :bar]
     checks_sparse "codes are unique", [1, :foo], [2, :foo]
     checks_sparse "columns are symbols", [1, :foo, [] => :baz]
 
-    checks_dense "id is Fixnum", [:id, :code], ["hello", :foo]
+    checks_dense "id is Integer", [:id, :code], ["hello", :foo]
     checks_dense "invalid code type", [:id, :code], [1, 2323]
     checks_dense "has id and code", [:id, :code, :other], [1,]
     checks_dense "codes are unique", [:id, :code], [1, :foo], [2, :foo]
@@ -238,7 +254,7 @@ class LocalDoggie
     dog.breed = Breed.corgi
     dog.breed = nil
     dog.breed_id.should be_nil
-    dog.breed.should be_nil
+    expect(dog.breed).to be_nil
     dog.anything = Breed.doberman
     dog.anything = nil
     dog.anything_id.should be_nil