Using objects in models (with CouchFoo)
Written on March 21, 2009 by george
ActiveRecord allows you to serialize objects into text columns through YAML. This seems useful but in my experience is under-used. One of the primary reasons for this is it’s not possible to use the data that the object encapsulates without the ruby model. For example it’s not possible to find on the contents of that object or for that matter, modify the object with languages that lack YAML support. With CouchDB all data is stored in JSON so this is not an issue.
The project I wrote CouchFoo for used complex ACLs and I wanted to encapsulate this all in an object rather than use several many-many relationships and construct an ACL object based on their contents. So how do you this with CouchFoo? Simple, any object can be assigned as a property in a CouchFoo model as long as it has a .to_json method and a class .from_json method. The methods do what you’d expect, for example:
class DataObjectAttributeList
attr_accessor :attributes
# Constructs the object from JSON
def self.from_json(json)
DataObjectAttributeList.new(json)
end
# Converts the object to JSON
def to_json
@attributes
end
def initialize(initials = {}, *args)
@attributes = initials
end
This is just a simple example storing a hash but the structure could be as complex as you’d like. In the future I plan to add inline associations to CouchFoo, so rather than have a one-to-many association where the many are accessed via a second database query you could have the objects stored as part of the parent contents. Performance wise, this is normally much more efficient (although not in all situations – eg heavy write and low read).
Overall, this becomes a very addictive way of developing and in the same way you start to question whether you need a relational database, you start to question whether you should store associated objects inline or separately.
