Add common concern with model_headers default

lib/tallty_import_export.rb

@@ -4,6 +4,7 @@ require 'axlsx'
 module TalltyImportExport
   class Error < StandardError; end
 
+  autoload :Common,     'tallty_import_export/common'
   autoload :Exportable,     'tallty_import_export/exportable'
   autoload :Importable,     'tallty_import_export/importable'
 end

lib/tallty_import_export/common.rb

+module TalltyImportExport
+  module Common
+    extend ActiveSupport::Concern
+
+    included do
+    end
+
+    module ClassMethods
+      def model_headers
+        columns.map do |column|
+          {
+            key: column.name,
+            name: column.comment || column.name,
+            attr_type: column.type,
+            format: column.type == :string ? :string : nil,
+          }
+        end
+      end
+    end
+  end
+end

lib/tallty_import_export/exportable.rb

@@ -2,6 +2,8 @@ module TalltyImportExport
   module Exportable
     extend ActiveSupport::Concern
 
+    include Common
+
     # export_headers / headers
     # key: 属性的英文名
     # name: 属性的中文名
@@ -56,7 +58,7 @@ module TalltyImportExport
         @row_height ||= options.delete(:row_height) || 35
         @width ||= options.delete(:width) || 30
         @filename ||= options.delete(:filename)
-        @headers = self.respond_to?(:export_headers) ? export_headers : headers
+        @headers = self.try(:export_headers) || self.try(:headers) || self.try(:model_headers)
         @headers.map! {|header| header.with_indifferent_access}
       end