Issues CSV view code extracted for reuse

app/controllers/projects/issues_controller.rb

@@ -37,8 +37,6 @@ class Projects::IssuesController < Projects::ApplicationController
 
     if params[:label_name].present?
       @labels = LabelsFinder.new(current_user, project_id: @project.id, title: params[:label_name]).execute
-    elsif request.format.csv?
-      @labels = @issues.labels_hash
     end
 
     @users = []
@@ -56,7 +54,9 @@ class Projects::IssuesController < Projects::ApplicationController
     respond_to do |format|
       format.html
       format.atom { render layout: false }
-      format.csv
+      format.csv do
+        render text: Issues::ExportCsvService.new(@issues).render
+      end
       format.json do
         render json: {
           html: view_to_html_string("projects/issues/_issues"),

app/services/issues/export_csv_service.rb

+module Issues
+  class ExportCsvService
+    def initialize(issues_relation)
+      @issues = issues_relation
+      @labels = @issues.labels_hash
+    end
+
+    def render
+      csv_builder.render
+    end
+
+    private
+
+    def csv_builder
+      @csv_builder ||= CsvBuilder.new(@issues.includes(:author, :assignee),
+                                       'Issue ID' => 'iid',
+                                       'Title' => 'title',
+                                       'State' => 'state',
+                                       'Description' => 'description',
+                                       'Author' => 'author_name',
+                                       'Assignee' => 'assignee_name',
+                                       'Confidential' => 'confidential',
+                                       'Due Date' => -> (issue) { issue.due_date&.to_s(:csv) },
+                                       'Created At (UTC)' => -> (issue) { issue.created_at&.to_s(:csv) },
+                                       'Updated At (UTC)' => -> (issue) { issue.updated_at&.to_s(:csv) },
+                                       'Milestone' => -> (issue) { issue.milestone&.title },
+                                       'Labels' => -> (issue) { @labels[issue.id].sort.join(',').presence }
+                                     )
+    end
+  end
+end

app/views/projects/issues/index.csv.ruby

-columns = {
-  'Issue ID' => 'iid',
-  'Title' => 'title',
-  'State' => 'state',
-  'Description' => 'description',
-  'Author' => 'author_name',
-  'Assignee' => 'assignee_name',
-  'Confidential' => 'confidential',
-  'Due Date' => -> (issue) { issue.due_date&.to_s(:csv) },
-  'Created At (UTC)' => -> (issue) { issue.created_at&.to_s(:csv) },
-  'Updated At (UTC)' => -> (issue) { issue.updated_at&.to_s(:csv) },
-  'Milestone' => -> (issue) { issue.milestone&.title },
-  'Labels' => -> (issue) { @labels[issue.id].sort.join(',').presence }
-}
-
-CsvBuilder.new(@issues.includes(:author, :assignee), columns).render