feature: extract! api for getting attributes from object (#32)

* feature: extract! api for getting attributes from object

* add key transformation to extract! syntax

README.md

@@ -155,6 +155,33 @@ The difference between the block form and inline form is
   2. The inline form is considered a leaf node, and you can only [search](#traversing)
   for internal nodes.
 
+### json.extract!
+Extracts attributes from object or hash in 1 line
+
+```ruby
+# without extract!
+json.id user.id
+json.email user.email
+json.firstName user.first_name
+
+# with extract!
+json.extract! user, :id, :email, :first_name
+
+# => {"id" => 1, "email" => "email@gmail.com", "first_name" => "user"}
+
+# with extract! with key transformation
+json.extract! user, :id, [:first_name, :firstName], [:last_name, :lastName]
+
+# => {"id" => 1, "firstName" => "user", "lastName" => "last"}
+```
+
+The inline form defines object and attributes
+
+| Parameter | Notes |
+| :--- | :--- |
+| object | An object |
+| attributes | A list of attributes |
+
 ### json.array!
 Generates an array of json objects.
 

lib/props_template.rb

@@ -22,6 +22,7 @@ class << self
     self.template_lookup_options = {handlers: [:props]}
 
     delegate :result!, :array!,
+      :extract!,
       :deferred!,
       :fragments!,
       :set_block_content!,

lib/props_template/base.rb

@@ -105,6 +105,28 @@ def array!(collection, options = {})
       nil
     end
 
+    # json.id item.id
+    # json.value item.value
+    #
+    # json.extract! item, :id, :value
+    #
+    # with key transformation
+    # json.extract! item, :id, [:first_name, :firstName]
+    def extract!(object, *values)
+      values.each do |value|
+        key, attribute = if value.is_a?(Array)
+          [value[1], value[0]]
+        else
+          [value, value]
+        end
+
+        set!(
+          key,
+          object.is_a?(Hash) ? object.fetch(attribute) : object.public_send(attribute)
+        )
+      end
+    end
+
     def result!
       if @scope.nil?
         @stream.push_object

spec/props_template_spec.rb

@@ -296,4 +296,53 @@
       }.to raise_error(Props::InvalidScopeForArrayError)
     end
   end
+
+  context "extract!" do
+    it "extracts values for hash" do
+      object = { :foo => "bar", "bar" => "foo", :wiz => "wiz" }
+
+      json = Props::Base.new
+      json.extract! object, :foo, "bar"
+      attrs = json.result!.strip
+
+      expect(attrs).to eql_json({
+        foo: "bar",
+        bar: "foo"
+      })
+    end
+
+    it "extracts values for hash with key transformation" do
+      object = { :foo => "bar", "bar_bar" => "foo", :wiz => "wiz" }
+
+      json = Props::Base.new
+      json.extract! object, :foo, ["bar_bar", "barBar"]
+      attrs = json.result!.strip
+
+      expect(attrs).to eql_json({
+        foo: "bar",
+        barBar: "foo"
+      })
+    end
+
+    it "extracts values for object" do
+      class FooBar
+        def foo
+          "bar"
+        end
+
+        def bar
+          "foo"
+        end
+      end
+
+      json = Props::Base.new
+      json.extract! FooBar.new, :foo, "bar"
+      attrs = json.result!.strip
+
+      expect(attrs).to eql_json({
+        foo: "bar",
+        bar: "foo"
+      })
+    end
+  end
 end