Don't allow category slugs that are numbers

app/models/category.rb

@@ -85,6 +85,11 @@ class Category < ActiveRecord::Base
     if name.present?
       self.slug = Slug.for(name)
 
+      # Reject slugs that only contain numbers, because that's indistinguishable from an id.
+      self.slug = '' unless self.slug =~ /[^\d]/
+
+      return if self.slug.blank?
+
       # If a category with that slug already exists, set the slug to nil so the category can be found
       # another way.
       category = Category.where(slug: self.slug)

spec/models/category_spec.rb

@@ -104,6 +104,14 @@ describe Category do
     end
   end
 
+  describe 'slug would be a number' do
+    let(:category) { Fabricate(:category, name: "電車男 2") }
+
+    it 'creates a blank slug' do
+      category.slug.should be_blank
+    end
+  end
+
   describe 'after create' do
     before do
       @category = Fabricate(:category, name: 'Amazing Category')