Ruby On Rails provides a few neat ways to serialise/deserialise objects to JSON. Out of the box you get the following approaches
SERIALISING
* json_string = a_house.to_json
DESERIALISING
* an_object = ActiveSupport::JSON.decode(json_string) # gives you an object of type Object
* a_house.from_json(json_string) # gives you an object of type House, note that a_house
# is an instance of House
These are pretty straightforward and do exactly what they say on the tin. Of the deserialising methods, note that using ActiveSupport directly gives you an object of type Object so you may prefer the stronger typing of the second technique which gives you an actual House object.
Note: There’s been some great improvements to JSON support built right into Rails since Rails 2 has come around. For more info on this see here.
When things just aren’t enough…
There are times when you will want to override the default serialisation that Rails provides - such as if you want to do some object ‘flattening’ like including an attribute from an association on serialising. Now before proceeding check out the latest Rails 2 JSON support mentioned at the end of the previous section as this might make your life a lot easier. Otherwise, let’s press on with an example of DIY JSON handling.
Given a House object which has an associated Owner object, you might want to include the Owner’s name attribute when serialising a House.
House Class
- has address and value attributes
- has an associated Owner object
Owner Class
- has a name attribute
We’ll need to override the default to_json method on the House model.
class House::Base
def to_json
result = Hash.new
self.class.content_columns.each do |column|
if self.attributes.include?(column.name)
result[column.name.to_sym] = self.send(column.name)
end
end
if self.attributes.include?(column.name)
result[:owner_name] = owner.name
end
result.to_json
end
end
The above was partially taken from the howtogeneratejson page on the Rails wiki, which is has little bit more detail. Now all you need to do is call the a_house.to_json method and you get lots of lovely JSON which represents your model! One final note is that you may not want to override the default to_json method. If not, just call your method something else like to_custom_json. Also, there’s
