Default values for posts/topics fields on Category

When creating categories (or, at least, subcategories), certain integer
values are set to a default of NULL: topics_week, topics_month,
topics_year, posts_week, posts_month, and posts_year. This causes
consistent exceptions when trying to visit `/categories`, with the
offending line being in
`CategoryDetailedSerializer#count_with_subcategories`. This attempts to
coerce nil into Fixnum.

A fix could be to convert to 0 in the code, but these attributes should
really never be NULL. If there are no posts or topics, they should be 0
to maintain data integrity.

Signed-off-by: David Celis <me@davidcel.is>

db/migrate/20140206195001_add_defaults_to_category_posts_and_topics_fields.rb

@@ -0,0 +1,11 @@
+class AddDefaultsToCategoryPostsAndTopicsFields < ActiveRecord::Migration
+  def change
+    change_column_default :categories, :posts_week,   0
+    change_column_default :categories, :posts_month,  0
+    change_column_default :categories, :posts_year,   0
+
+    change_column_default :categories, :topics_week,  0
+    change_column_default :categories, :topics_month, 0
+    change_column_default :categories, :topics_year,  0
+  end
+end

spec/models/category_spec.rb

@@ -206,6 +206,14 @@ describe Category do
       @topic.posts.count.should == 1
 
       @category.topic_url.should be_present
+
+      @category.posts_week.should  == 0
+      @category.posts_month.should == 0
+      @category.posts_year.should  == 0
+
+      @category.topics_week.should  == 0
+      @category.topics_month.should == 0
+      @category.topics_year.should  == 0
     end
 
     it "should not set its description topic to auto-close" do