add support for read only post queries

app/models/post.rb

@@ -1513,8 +1513,12 @@ class Post < ActiveRecord::Base
       where("posts.tag_index @@ to_tsquery('danbooru', E?)", tag.to_escaped_for_tsquery)
     end
 
-    def tag_match(query)
-      PostQueryBuilder.new(query).build
+    def tag_match(query, read_only = false)
+      if read_only
+        PostQueryBuilder.new(query).build(PostReadOnly.where("true"))
+      else
+        PostQueryBuilder.new(query).build
+      end
     end
 
     def positive

app/models/post_read_only.rb

@@ -0,0 +1,4 @@
+class PostReadOnly < Post
+  establish_connection "ro_#{Rails.env}".to_sym
+  attr_readonly *column_names
+end