Question

store as Hash Table with Hstore, wrong ordering in Hash after Save

class Service < ActiveRecord::Base
  serialize :properties, ActiveRecord::Coders::Hstore
end

service = Service.new
service.properties = { "aaa" => 1, "zz" => 2, "cc" => 3, "d" => 4 }
#=> { "aaa" => 1, "zz" => 2, "cc" => 3, "d" => 4 }
service.save
reload!
service = Service.find(:id)
service.properties
#=> { "d" => "4", "cc" => "3", "zz" => 2, "aaa" => 1 }
Bug::: wrong ordering after save

Is it because after serialize that it orders by Tree. Any ideas or anyone had faced this problem before? Thanks in advance.

Answer 1

From the fine PostgreSQL manual:

F.16. hstore
[…]
This module implements the hstore data type for storing sets of key/value pairs within a single PostgreSQL value.
[…]
The order of the pairs is not significant (and may not be reproduced on output).

So PostgreSQL’s hstore type is an unordered set of key/value pairs that doesn’t guarantee any particular order of the key/value pairs. Once your Ruby Hash is converted to an hstore, the ordering is lost.

If you need to maintain the order in your Hash you’ll have to use a different serialize format.