diff --git a/jsonapi-deserializable.gemspec b/jsonapi-deserializable.gemspec
index d47611f..4a5780c 100644
--- a/jsonapi-deserializable.gemspec
+++ b/jsonapi-deserializable.gemspec
@@ -16,4 +16,5 @@ Gem::Specification.new do |spec|
 
   spec.add_development_dependency 'rake', '>=0.9'
   spec.add_development_dependency 'rspec', '~>3.4'
+  spec.add_development_dependency 'codecov', '~> 0.1'
 end
diff --git a/lib/jsonapi/deserializable/relationship.rb b/lib/jsonapi/deserializable/relationship.rb
index eb2192f..deb87fd 100644
--- a/lib/jsonapi/deserializable/relationship.rb
+++ b/lib/jsonapi/deserializable/relationship.rb
@@ -33,16 +33,26 @@ module JSONAPI
       def deserialize!
         @hash = {}
         if @data.is_a?(Array)
-          ids = @data.map { |ri| ri['id'] }
-          types = @data.map { |ri| ri['type'] }
-          instance_exec(@document, ids, types, &self.class.has_many_block)
+          deserialize_has_many!
         else
-          id = @data && @data['id']
-          type = @data && @data['type']
-          instance_exec(@document, id, type, &self.class.has_one_block)
+          deserialize_has_one!
         end
       end
 
+      def deserialize_has_one!
+        return unless self.class.has_one_block && @document.key?('data')
+        id = @data && @data['id']
+        type = @data && @data['type']
+        instance_exec(@document, id, type, &self.class.has_one_block)
+      end
+
+      def deserialize_has_many!
+        return unless self.class.has_many_block
+        ids = @data.map { |ri| ri['id'] }
+        types = @data.map { |ri| ri['type'] }
+        instance_exec(@document, ids, types, &self.class.has_many_block)
+      end
+
       def field(hash)
         @hash.merge!(hash)
       end
diff --git a/lib/jsonapi/deserializable/relationship_dsl.rb b/lib/jsonapi/deserializable/relationship_dsl.rb
index f49b196..92adf2a 100644
--- a/lib/jsonapi/deserializable/relationship_dsl.rb
+++ b/lib/jsonapi/deserializable/relationship_dsl.rb
@@ -7,12 +7,12 @@ module JSONAPI
 
       module ClassMethods
         def has_one(&block)
-          block ||= proc { |rel| field key.to_sym => rel }
+          block ||= proc { |rel| field relationship: rel }
           self.has_one_block = block
         end
 
         def has_many(&block)
-          block ||= proc { |rel| field key.to_sym => rel }
+          block ||= proc { |rel| field relationship: rel }
           self.has_many_block = block
         end
       end
diff --git a/spec/deserializable_relationships_spec.rb b/spec/deserializable_relationships_spec.rb
deleted file mode 100644
index 5c1d1eb..0000000
--- a/spec/deserializable_relationships_spec.rb
+++ /dev/null
@@ -1,44 +0,0 @@
-require 'jsonapi/deserializable'
-
-describe JSONAPI::Deserializable::Relationship, '#to_h' do
-  it 'deserializes has_one relationships' do
-    deserializable_klass = Class.new(JSONAPI::Deserializable::Relationship) do
-      has_one do |rel|
-        field sponsor_id: (rel['data'] && rel['data']['id'])
-      end
-    end
-
-    payload = {
-      'data' => {
-        'type' => 'users',
-        'id' => '1'
-      }
-    }
-
-    actual = deserializable_klass.(payload)
-    expected = { sponsor_id: '1' }
-
-    expect(actual).to eq(expected)
-  end
-
-  it 'deserializes has_many relationships' do
-    deserializable_klass = Class.new(JSONAPI::Deserializable::Relationship) do
-      has_many do |rel|
-        field post_ids: rel['data'].map { |ri| ri['id'] }
-      end
-    end
-
-    payload = {
-      'data' => [
-        { 'type' => 'postd', 'id' => '1' },
-        { 'type' => 'postd', 'id' => '2' },
-        { 'type' => 'postd', 'id' => '3' }
-      ]
-    }
-
-    actual = deserializable_klass.(payload)
-    expected = { post_ids: %w(1 2 3) }
-
-    expect(actual).to eq(expected)
-  end
-end
diff --git a/spec/deserializable_resource_spec.rb b/spec/deserializable_resource_spec.rb
deleted file mode 100644
index ea11d9c..0000000
--- a/spec/deserializable_resource_spec.rb
+++ /dev/null
@@ -1,132 +0,0 @@
-require 'jsonapi/deserializable'
-
-describe JSONAPI::Deserializable::Resource, '#to_h' do
-  before(:all) do
-    @payload = {
-      'data' => {
-        'id' => '1',
-        'type' => 'users',
-        'attributes' => {
-          'name' => 'Name',
-          'address' => 'Address'
-        },
-        'relationships' => {
-          'sponsor' => {
-            'data' => { 'type' => 'users', 'id' => '1337' }
-          },
-          'posts' => {
-            'data' => [
-              { 'type' => 'posts', 'id' => '123' },
-              { 'type' => 'posts', 'id' => '234' },
-              { 'type' => 'posts', 'id' => '345' }
-            ]
-          }
-        }
-      }
-    }
-  end
-
-  it 'deserializes primary type' do
-    deserializable_klass = Class.new(JSONAPI::Deserializable::Resource) do
-      type { |type| field type: type }
-    end
-
-    actual = deserializable_klass.(@payload)
-    expected = { type: 'users' }
-
-    expect(actual).to eq(expected)
-  end
-
-  it 'deserializes primary id when present' do
-    deserializable_klass = Class.new(JSONAPI::Deserializable::Resource) do
-      id { |id| field id: id }
-    end
-
-    actual = deserializable_klass.(@payload)
-    expected = { id: '1' }
-
-    expect(actual).to eq(expected)
-  end
-
-  it 'does not deserialize primary id when absent' do
-    deserializable_klass = Class.new(JSONAPI::Deserializable::Resource) do
-      id { |id| field id: id }
-    end
-
-    payload = {
-      'data' => { 'type' => 'users' }
-    }
-    actual = deserializable_klass.(payload)
-    expected = {}
-
-    expect(actual).to eq(expected)
-  end
-
-  it 'handles attributes' do
-    deserializable_klass = Class.new(JSONAPI::Deserializable::Resource) do
-      attribute(:name) { |name| field username: name }
-      attribute(:address) { |address| field address: address }
-    end
-
-    actual = deserializable_klass.(@payload)
-    expected = {
-      username: 'Name',
-      address: 'Address'
-    }
-
-    expect(actual).to eq(expected)
-  end
-
-  it 'handles has_one relationships' do
-    deserializable_klass = Class.new(JSONAPI::Deserializable::Resource) do
-      has_one(:sponsor) { |rel| field sponsor_id: rel['data']['id'] }
-    end
-
-    actual = deserializable_klass.(@payload)
-    expected = {
-      sponsor_id: '1337'
-    }
-
-    expect(actual).to eq(expected)
-  end
-
-  it 'handles has_many relationships' do
-    deserializable_klass = Class.new(JSONAPI::Deserializable::Resource) do
-      has_many(:posts) do |rel|
-        field post_ids: rel['data'].map { |ri| ri['id'] }
-      end
-    end
-
-    actual = deserializable_klass.(@payload)
-    expected = {
-      post_ids: %w(123 234 345)
-    }
-
-    expect(actual).to eq(expected)
-  end
-
-  it 'works' do
-    deserializable_klass = Class.new(JSONAPI::Deserializable::Resource) do
-      id
-      attribute(:name) { |name| field username: name }
-      attribute :address
-      has_one :sponsor do |_, id|
-        field sponsor_id: id
-      end
-      has_many :posts do |_, ids|
-        field post_ids: ids
-      end
-    end
-
-    actual = deserializable_klass.(@payload)
-    expected = {
-      id: '1',
-      username: 'Name',
-      address: 'Address',
-      sponsor_id: '1337',
-      post_ids: %w(123 234 345)
-    }
-
-    expect(actual).to eq(expected)
-  end
-end
diff --git a/spec/relationship/has_many_spec.rb b/spec/relationship/has_many_spec.rb
new file mode 100644
index 0000000..d13085d
--- /dev/null
+++ b/spec/relationship/has_many_spec.rb
@@ -0,0 +1,72 @@
+require 'spec_helper'
+
+describe JSONAPI::Deserializable::Relationship, '.has_many' do
+  let(:deserializable_foo) do
+    Class.new(JSONAPI::Deserializable::Relationship) do
+      has_many do |rel, ids, types|
+        field foo_ids: ids
+        field foo_types: types
+        field foo_rel: rel
+      end
+    end
+  end
+
+  context 'relationship is not empty' do
+    let(:payload) do
+      {
+        'data' => [
+          { 'type' => 'foo', 'id' => 'bar' },
+          { 'type' => 'foo', 'id' => 'baz' }
+        ]
+      }
+    end
+
+    it 'creates corresponding fields' do
+      actual = deserializable_foo.call(payload)
+      expected = { foo_ids: %w(bar baz), foo_types: %w(foo foo),
+                   foo_rel: payload }
+
+      expect(actual).to eq(expected)
+    end
+
+    it 'defaults to creating a relationship field' do
+      klass = Class.new(JSONAPI::Deserializable::Relationship) do
+        has_many
+      end
+      actual = klass.call(payload)
+      expected = { relationship: payload }
+
+      expect(actual).to eq(expected)
+    end
+  end
+
+  context 'relationship is empty' do
+    it 'creates corresponding fields' do
+      payload = { 'data' => [] }
+      actual = deserializable_foo.call(payload)
+      expected = { foo_ids: [], foo_types: [], foo_rel: payload }
+
+      expect(actual).to eq(expected)
+    end
+  end
+
+  context 'data is absent' do
+    it 'does not create corresponding fields' do
+      payload = {}
+      actual = deserializable_foo.call(payload)
+      expected = {}
+
+      expect(actual).to eq(expected)
+    end
+  end
+
+  context 'relationship is not to-many' do
+    it 'does not create corresponding fields' do
+      payload = { 'data' => nil }
+      actual = deserializable_foo.call(payload)
+      expected = {}
+
+      expect(actual).to eq(expected)
+    end
+  end
+end
diff --git a/spec/relationship/has_one_spec.rb b/spec/relationship/has_one_spec.rb
new file mode 100644
index 0000000..fe9f0c6
--- /dev/null
+++ b/spec/relationship/has_one_spec.rb
@@ -0,0 +1,66 @@
+require 'spec_helper'
+
+describe JSONAPI::Deserializable::Relationship, '.has_one' do
+  let(:deserializable_foo) do
+    Class.new(JSONAPI::Deserializable::Relationship) do
+      has_one do |rel, id, type|
+        field foo_id: id
+        field foo_type: type
+        field foo_rel: rel
+      end
+    end
+  end
+
+  context 'relationship is not nil' do
+    let(:payload) do
+      { 'data' => { 'type' => 'foo', 'id' => 'bar' } }
+    end
+
+    it 'creates corresponding fields' do
+      actual = deserializable_foo.call(payload)
+      expected = { foo_id: 'bar', foo_type: 'foo', foo_rel: payload }
+
+      expect(actual).to eq(expected)
+    end
+
+    it 'defaults to creating a relationship field' do
+      klass = Class.new(JSONAPI::Deserializable::Relationship) do
+        has_one
+      end
+      actual = klass.call(payload)
+      expected = { relationship: payload }
+
+      expect(actual).to eq(expected)
+    end
+  end
+
+  context 'relationship is nil' do
+    it 'creates corresponding fields' do
+      payload = { 'data' => nil }
+      actual = deserializable_foo.call(payload)
+      expected = { foo_id: nil, foo_type: nil, foo_rel: payload }
+
+      expect(actual).to eq(expected)
+    end
+  end
+
+  context 'data is absent' do
+    it 'does not create corresponding fields' do
+      payload = {}
+      actual = deserializable_foo.call(payload)
+      expected = {}
+
+      expect(actual).to eq(expected)
+    end
+  end
+
+  context 'relationship is not to-one' do
+    it 'does not create corresponding fields' do
+      payload = { 'data' => [] }
+      actual = deserializable_foo.call(payload)
+      expected = {}
+
+      expect(actual).to eq(expected)
+    end
+  end
+end
diff --git a/spec/resource/DSL/attribute_spec.rb b/spec/resource/DSL/attribute_spec.rb
new file mode 100644
index 0000000..da97f6f
--- /dev/null
+++ b/spec/resource/DSL/attribute_spec.rb
@@ -0,0 +1,57 @@
+require 'spec_helper'
+
+describe JSONAPI::Deserializable::Resource, '.attribute' do
+  it 'creates corresponding field if attribute is present' do
+    payload = {
+      'data' => {
+        'type' => 'foo',
+        'attributes' => { 'foo' => 'bar' }
+      }
+    }
+    klass = Class.new(JSONAPI::Deserializable::Resource) do
+      attribute(:foo) { |foo| field foo: foo }
+    end
+    actual = klass.call(payload)
+    expected = { foo: 'bar' }
+
+    expect(actual).to eq(expected)
+  end
+
+  it 'does not create corresponding field if attribute is absent' do
+    payload = { 'data' => { 'type' => 'foo' }, 'attributes' => {} }
+    klass = Class.new(JSONAPI::Deserializable::Resource) do
+      attribute(:foo) { |foo| field foo: foo }
+    end
+    actual = klass.call(payload)
+    expected = {}
+
+    expect(actual).to eq(expected)
+  end
+
+  it 'does not create corresponding field if no attribute specified' do
+    payload = { 'data' => { 'type' => 'foo' } }
+    klass = Class.new(JSONAPI::Deserializable::Resource) do
+      attribute(:foo) { |foo| field foo: foo }
+    end
+    actual = klass.call(payload)
+    expected = {}
+
+    expect(actual).to eq(expected)
+  end
+
+  it 'defaults to creating a field with same name' do
+    payload = {
+      'data' => {
+        'type' => 'foo',
+        'attributes' => { 'foo' => 'bar' }
+      }
+    }
+    klass = Class.new(JSONAPI::Deserializable::Resource) do
+      attribute :foo
+    end
+    actual = klass.call(payload)
+    expected = { foo: 'bar' }
+
+    expect(actual).to eq(expected)
+  end
+end
diff --git a/spec/resource/DSL/has_many_spec.rb b/spec/resource/DSL/has_many_spec.rb
new file mode 100644
index 0000000..29c9a38
--- /dev/null
+++ b/spec/resource/DSL/has_many_spec.rb
@@ -0,0 +1,118 @@
+require 'spec_helper'
+
+describe JSONAPI::Deserializable::Resource, '.has_many' do
+  let(:deserializable_foo) do
+    Class.new(JSONAPI::Deserializable::Resource) do
+      has_many :foo do |rel, ids, types|
+        field foo_ids: ids
+        field foo_types: types
+        field foo_rel: rel
+      end
+    end
+  end
+
+  context 'relationship is not empty' do
+    let(:payload) do
+      {
+        'data' => {
+          'type' => 'foo',
+          'relationships' => {
+            'foo' => {
+              'data' => [
+                { 'type' => 'foo', 'id' => 'bar' },
+                { 'type' => 'foo', 'id' => 'baz' }
+              ]
+            }
+          }
+        }
+      }
+    end
+
+    it 'creates corresponding fields' do
+      actual = deserializable_foo.call(payload)
+      expected = { foo_ids: %w(bar baz), foo_types: %w(foo foo),
+                   foo_rel: payload['data']['relationships']['foo'] }
+
+      expect(actual).to eq(expected)
+    end
+
+    it 'defaults to creating a field of the same name' do
+      klass = Class.new(JSONAPI::Deserializable::Resource) do
+        has_many :foo
+      end
+      actual = klass.call(payload)
+      expected = { foo: payload['data']['relationships']['foo'] }
+
+      expect(actual).to eq(expected)
+    end
+  end
+
+  context 'relationship is empty' do
+    it 'creates corresponding fields' do
+      payload = {
+        'data' => {
+          'type' => 'foo',
+          'relationships' => {
+            'foo' => {
+              'data' => []
+            }
+          }
+        }
+      }
+      actual = deserializable_foo.call(payload)
+      expected = { foo_ids: [], foo_types: [],
+                   foo_rel: payload['data']['relationships']['foo'] }
+
+      expect(actual).to eq(expected)
+    end
+  end
+
+  context 'relationship is absent' do
+    it 'does not create corresponding fields' do
+      payload = {
+        'data' => {
+          'type' => 'foo',
+          'relationships' => {}
+        }
+      }
+      actual = deserializable_foo.call(payload)
+      expected = {}
+
+      expect(actual).to eq(expected)
+    end
+  end
+
+  context 'there is no relationships member' do
+    it 'does not create corresponding fields' do
+      payload = {
+        'data' => {
+          'type' => 'foo'
+        }
+      }
+      actual = deserializable_foo.call(payload)
+      expected = {}
+
+      expect(actual).to eq(expected)
+    end
+  end
+
+  context 'relationship is not to-many' do
+    it 'does not create corresponding fields' do
+      payload = {
+        'data' => {
+          'type' => 'foo',
+          'relationships' => {
+            'foo' => {
+              'data' => { 'type' => 'foo', 'id' => 'bar' }
+            }
+          }
+        }
+      }
+
+      actual = deserializable_foo.call(payload)
+      expected = {}
+
+      expect(actual).to eq(expected)
+    end
+  end
+end
diff --git a/spec/resource/DSL/has_one_spec.rb b/spec/resource/DSL/has_one_spec.rb
new file mode 100644
index 0000000..4869e23
--- /dev/null
+++ b/spec/resource/DSL/has_one_spec.rb
@@ -0,0 +1,114 @@
+require 'spec_helper'
+
+describe JSONAPI::Deserializable::Resource, '.has_one' do
+  let(:deserializable_foo) do
+    Class.new(JSONAPI::Deserializable::Resource) do
+      has_one :foo do |rel, id, type|
+        field foo_id: id
+        field foo_type: type
+        field foo_rel: rel
+      end
+    end
+  end
+
+  context 'relationship is not nil' do
+    let(:payload) do
+      {
+        'data' => {
+          'type' => 'foo',
+          'relationships' => {
+            'foo' => {
+              'data' => { 'type' => 'foo', 'id' => 'bar' }
+            }
+          }
+        }
+      }
+    end
+
+    it 'creates corresponding fields' do
+      actual = deserializable_foo.call(payload)
+      expected = { foo_id: 'bar', foo_type: 'foo',
+                   foo_rel: payload['data']['relationships']['foo'] }
+
+      expect(actual).to eq(expected)
+    end
+
+    it 'defaults to creating a field of the same name' do
+      klass = Class.new(JSONAPI::Deserializable::Resource) do
+        has_one :foo
+      end
+      actual = klass.call(payload)
+      expected = { foo: payload['data']['relationships']['foo'] }
+
+      expect(actual).to eq(expected)
+    end
+  end
+
+  context 'relationship is nil' do
+    it 'creates corresponding fields' do
+      payload = {
+        'data' => {
+          'type' => 'foo',
+          'relationships' => {
+            'foo' => {
+              'data' => nil
+            }
+          }
+        }
+      }
+      actual = deserializable_foo.call(payload)
+      expected = { foo_id: nil, foo_type: nil,
+                   foo_rel: payload['data']['relationships']['foo'] }
+
+      expect(actual).to eq(expected)
+    end
+  end
+
+  context 'relationship is absent' do
+    it 'does not create corresponding fields' do
+      payload = {
+        'data' => {
+          'type' => 'foo',
+          'relationships' => {}
+        }
+      }
+      actual = deserializable_foo.call(payload)
+      expected = {}
+
+      expect(actual).to eq(expected)
+    end
+  end
+
+  context 'there is no relationships member' do
+    it 'does not create corresponding fields' do
+      payload = {
+        'data' => {
+          'type' => 'foo'
+        }
+      }
+      actual = deserializable_foo.call(payload)
+      expected = {}
+
+      expect(actual).to eq(expected)
+    end
+  end
+
+  context 'relationship is not to-one' do
+    it 'does not create corresponding fields' do
+      payload = {
+        'data' => {
+          'type' => 'foo',
+          'relationships' => {
+            'foo' => {
+              'data' => []
+            }
+          }
+        }
+      }
+      actual = deserializable_foo.call(payload)
+      expected = {}
+
+      expect(actual).to eq(expected)
+    end
+  end
+end
diff --git a/spec/resource/DSL/id_spec.rb b/spec/resource/DSL/id_spec.rb
new file mode 100644
index 0000000..1a02b44
--- /dev/null
+++ b/spec/resource/DSL/id_spec.rb
@@ -0,0 +1,36 @@
+require 'spec_helper'
+
+describe JSONAPI::Deserializable::Resource, '.id' do
+  it 'creates corresponding field if id is present' do
+    payload = { 'data' => { 'type' => 'foo', 'id' => 'bar' } }
+    klass = Class.new(JSONAPI::Deserializable::Resource) do
+      id { |i| field id: i }
+    end
+    actual = klass.call(payload)
+    expected = { id: 'bar' }
+
+    expect(actual).to eq(expected)
+  end
+
+  it 'does not create corresponding field if id is absent' do
+    payload = { 'data' => { 'type' => 'foo' } }
+    klass = Class.new(JSONAPI::Deserializable::Resource) do
+      id { |i| field id: i }
+    end
+    actual = klass.call(payload)
+    expected = {}
+
+    expect(actual).to eq(expected)
+  end
+
+  it 'defaults to creating an id field' do
+    payload = { 'data' => { 'type' => 'foo', 'id' => 'bar' } }
+    klass = Class.new(JSONAPI::Deserializable::Resource) do
+      id
+    end
+    actual = klass.call(payload)
+    expected = { id: 'bar' }
+
+    expect(actual).to eq(expected)
+  end
+end
diff --git a/spec/resource/DSL/type_spec.rb b/spec/resource/DSL/type_spec.rb
new file mode 100644
index 0000000..eabcb32
--- /dev/null
+++ b/spec/resource/DSL/type_spec.rb
@@ -0,0 +1,25 @@
+require 'spec_helper'
+
+describe JSONAPI::Deserializable::Resource, '.type' do
+  it 'creates corresponding field' do
+    payload = { 'data' => { 'type' => 'foo' } }
+    klass = Class.new(JSONAPI::Deserializable::Resource) do
+      type { |t| field type: t }
+    end
+    actual = klass.call(payload)
+    expected = { type: 'foo' }
+
+    expect(actual).to eq(expected)
+  end
+
+  it 'defaults to creating a type field' do
+    payload = { 'data' => { 'type' => 'foo' } }
+    klass = Class.new(JSONAPI::Deserializable::Resource) do
+      type
+    end
+    actual = klass.call(payload)
+    expected = { type: 'foo' }
+
+    expect(actual).to eq(expected)
+  end
+end
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
new file mode 100644
index 0000000..95576cd
--- /dev/null
+++ b/spec/spec_helper.rb
@@ -0,0 +1,7 @@
+require 'simplecov'
+SimpleCov.start
+
+require 'codecov'
+SimpleCov.formatter = SimpleCov::Formatter::Codecov
+
+require 'jsonapi/deserializable'