Delegate missing methods in CSV block to current view context

app/views/active_admin/resource/index.csv.erb

@@ -3,7 +3,7 @@
 
   default = active_admin_application.csv_options
   options = default.merge active_admin_config.csv_builder.options
-  columns = active_admin_config.csv_builder.columns
+  columns = active_admin_config.csv_builder.render_columns(self)
 
   csv_output = CSV.generate(options) do |csv|
     csv << columns.map(&:name)

lib/active_admin/csv_builder.rb

@@ -17,27 +17,47 @@ class CSVBuilder
     # The CSVBuilder's columns would be Id followed by this
     # resource's content columns
     def self.default_for_resource(resource)
-      new(resource: resource).tap do |csv_builder|
-        csv_builder.column(:id)
+      new(resource: resource) do
+        column(:id)
         resource.content_columns.each do |content_column|
-          csv_builder.column(content_column.name.to_sym)
+          column(content_column.name.to_sym)
         end
       end
     end
 
-    attr_reader :columns, :options
+    attr_reader :columns, :options, :view_context
 
     def initialize(options={}, &block)
       @resource = options.delete(:resource)
-      @columns, @options = [], options
-      instance_exec &block if block_given?
+      @columns, @options, @block = [], options, block
     end
 
     # Add a column
     def column(name, &block)
       @columns << Column.new(name, @resource, block)
     end
 
+    # Runs the `csv` dsl block and render our columns
+    # Called from `index.csv.erb`, which passes in the current view context.
+    # This provides methods that could be called in the views to be called within
+    # the CSV block. Any method not defined on the CSV builder will instead be
+    # sent to the view context in order to emulate the capabilities of the `index`
+    # DSL.
+    def render_columns(view_context = nil)
+      @view_context = view_context
+      @columns = [] # we want to re-render these every instance
+      instance_eval &@block if @block.present?
+      columns
+    end
+
+    def method_missing(method, *args, &block)
+      if @view_context.respond_to?(method)
+        @view_context.send(method, *args, &block)
+      else
+        super
+      end
+    end
+
     class Column
       attr_reader :name, :data
 

spec/unit/csv_builder_spec.rb

@@ -3,7 +3,7 @@
 describe ActiveAdmin::CSVBuilder do
 
   describe '.default_for_resource using Post' do
-    let(:csv_builder) { ActiveAdmin::CSVBuilder.default_for_resource(Post) }
+    let(:csv_builder) { ActiveAdmin::CSVBuilder.default_for_resource(Post).tap(&:render_columns) }
 
     it 'returns a default csv_builder for Post' do
       expect(csv_builder).to be_a(ActiveAdmin::CSVBuilder)
@@ -37,7 +37,7 @@
   end
 
   context 'when empty' do
-    let(:builder){ ActiveAdmin::CSVBuilder.new }
+    let(:builder){ ActiveAdmin::CSVBuilder.new.tap(&:render_columns) }
 
     it "should have no columns" do
       expect(builder.columns).to eq []
@@ -48,7 +48,7 @@
     let(:builder) do
       ActiveAdmin::CSVBuilder.new do
         column :title
-      end
+      end.tap(&:render_columns)
     end
 
     it "should have one column" do
@@ -74,7 +74,7 @@
         column "My title" do
           # nothing
         end
-      end
+      end.tap(&:render_columns)
     end
 
     it "should have one column" do
@@ -96,7 +96,7 @@
 
   context "with a separator" do
     let(:builder) do
-      ActiveAdmin::CSVBuilder.new :col_sep => ";"
+      ActiveAdmin::CSVBuilder.new(:col_sep => ";").tap(&:render_columns)
     end
 
     it "should have proper separator" do
@@ -106,12 +106,29 @@
 
   context "with csv_options" do
     let(:builder) do
-      ActiveAdmin::CSVBuilder.new :force_quotes => true
+      ActiveAdmin::CSVBuilder.new(:force_quotes => true).tap(&:render_columns)
     end
 
     it "should have proper separator" do
       expect(builder.options).to eq({:force_quotes => true})
     end
   end
 
+  context "with access to the controller" do
+    let(:dummy_view_context) { double(controller: dummy_controller) }
+    let(:dummy_controller) { double(names: %w(title summary updated_at created_at))}
+    let(:builder) do
+      ActiveAdmin::CSVBuilder.new do
+        column "id"
+        controller.names.each do |name|
+          column(name)
+        end
+      end.tap{|b| b.render_columns(dummy_view_context)}
+    end
+
+    it "should render columns provided by the controller" do
+      expect(builder.columns.map(&:data)).to match_array([:id, :title, :summary, :updated_at, :created_at])
+    end
+  end
+
 end

spec/unit/resource_spec.rb

@@ -196,7 +196,7 @@ def config(options = {})
     describe "#csv_builder" do
       context "when no csv builder set" do
         it "should return a default column builder with id and content columns" do
-          expect(config.csv_builder.columns.size).to eq Category.content_columns.size + 1
+          expect(config.csv_builder.render_columns.size).to eq Category.content_columns.size + 1
         end
       end