```ruby
def to_json(options = {})
if options.empty?
super :only => [:id, :name]
else
super options
end
end
```
Now post.to\_json will only include the id and name attributes.
Note that for arrays of objects--at least with Rails 2.3.4--you need use the same parameters on the array.to\_json method:
```ruby
Post.all.to_json :only => [:id, :name]
```