Goodbye serialize, hello hstore.

You need dynamic columns in your tables. What do you do?

• Create lots of tables to handle it. Nice, now you’ll need more models and lots of additional sqls. Insertion and selection will be slow as hell.
• Use a noSQL database just for this issue. Good luck.
• Create a serialized column. Nice, insertion will be fine, and reading data from a record too. But, what if you have a condition in your select that includes serialized data? Yeah, regular expressions.

Requirements

Postgresql 8.4+ (also tested with 9.0) with contrib and Rails 3. (It might work on 2.3.x with minor patches…)
On Ubuntu, this is easy: sudo apt-get install postgresql-contrib-9.0

On Mac …you are screwed. Use a VM. you should use the binary package kindly provided by EnterpriseDB
Homebrew’s Postgres installation also includes the contrib packages: brew install postgres

Notes for Rails 3.1 and above

The master branch already support a custom serialization coder.
If you want to use it just put in your Gemfile:

gem 'activerecord-postgres-hstore', git: 'git://github.com/softa/activerecord-postgres-hstore.git'

If you install them gem from the master branch you also have to insert a line in each model that uses hstore.
Assuming a model called Person, with a data field on it, the code should look like:

class Person < ActiveRecord::Base
  serialize :data, ActiveRecord::Coders::Hstore
end

Install

Hstore is a PostgreSQL contrib type, check it out first.

Then, just add this to your Gemfile:

gem 'activerecord-postgres-hstore'

And run your bundler:

bundle install

Make sure that you have the desired database, if not create it as the desired user:

createdb hstorage_dev

Add the parameters to your database.yml (these are system dependant), e.g.:

development:
  adapter: postgresql
  host: 127.0.0.1
  database: hstorage_dev
  encoding: unicode
  username: postgres
  password: 
  pool: 5

Now you need to create a migration that adds hstore support for your PostgreSQL database:

rails g hstore:setup

Run it:

rake db:migrate

Finally you can create your own tables using hstore type. It’s easy:

rails g model Person name:string data:hstore
rake db:migrate

You’re done.
Well, not yet. Don’t forget to add indexes. Like this:

CREATE INDEX people_gist_data ON people USING GIST(data);
or
CREATE INDEX people_gin_data ON people USING GIN(data);

To understand the difference between the two types of indexes take a look at PostgreSQL docs.

Usage

Once you have it installed, you just need to learn a little bit of new sqls for selecting stuff (creating and updating is transparent).
Find records that contains a key named 'foo’:

Person.where("data ? 'foo'")

Find records where 'foo’ is equal to 'bar’:

Person.where("data -> 'foo' = 'bar'")

This same sql is at least twice as fast (using indexes) if you do it that way:

Person.where("data > 'foo=>bar’")

Find records where 'foo’ is not equal to 'bar’:

Person.where("data -> 'foo' <> 'bar'")

Find records where 'foo’ is like 'bar’:

Person.where("data -> 'foo' LIKE '%bar%'")

If you need to delete a key in a record, you can do it that way:

person.destroy_key(:data, :foo)

This way you’ll also save the record:

person.destroy_key!(:data, :foo)

The destroy_key method returns 'self’, so you can chain it:

person.destroy_key(:data, :foo).destroy_key(:data, :bar).save

But there is a shortcuts for that:

person.destroy_keys(:data, :foo, :bar)

And finally, if you need to delete keys in many rows, you can:

Person.delete_key(:data, :foo)

and with many keys:

Person.delete_keys(:data, :foo, :bar)

Have fun.

Help

You can use issues in github for that. Or else you can reach us at twitter: @dbiazus or @joaomilho

Note on Patches/Pull Requests

• Fork the project.
• Make your feature addition or bug fix.
• Add tests for it. This is important so I don’t break it in a future version unintentionally.
• Commit, do not mess with rakefile, version, or history. (if you want to have your own version, that is fine but bump version in a commit by itself I can ignore when I pull)
• Send me a pull request. Bonus points for topic branches.

Copyright

Copyright © 2010 Juan Maiz. See LICENSE for details.