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.

action	serialize	hstore	serialize sql	hstore sql
count all with condition	10114,575	1830,444	SELECT count(*) FROM foos WHERE data ~ ‘foo: bar’;	SELECT count(*) FROM bars WHERE data @> ‘foo=>bar’;
count all with negative condition	18722,149	1677,948	SELECT count(*) FROM foos WHERE data !~ ‘another key: 9999990’;	SELECT count(*) FROM bars WHERE not data @> ‘“another key”=>9999990’;
find one with condition	17740,307	130,227	SELECT count(*) FROM foos WHERE data ~ ‘another key: 9999990’;	SELECT * FROM bars WHERE data @> ‘“another key”=>9999990’

Benchmarks made in my local machine, with a million records. Time is in milliseconds.

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

Install

Hstore is a postgres contrib type. Check it out first:

http://www.postgresql.org/docs/9.0/static/hstore.html

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 my experience GIN is faster for searching records.

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'")
or
Person.where("not data @> 'foo=>bar'")

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

Person.where("data -> 'foo' LIKE '%bar%'")
or something like …
Person.where("data -> 'foo' ILIKE '%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 it a shortcut for that:

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

or…

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 me at twitter: @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.

License

gisborne/activerecord-postgres-hstore

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