Use Regexp as the value for any finder in ActiveRecord


Build Status Code Climate Test Coverage

Regexp support to ActiveRecord finders.


Wherex is Semantically Versioned, meaning that we will always indicate a backwardly incompatible change with a MAJOR version bump, so you can just use this in your Gemfile:

gem 'wherex', '~> 1.0'

Only works with Rails >= 3.1


# find users in 93, 94 and 95 (5 digit) zipcodes (new style finder)
User.where :zipcode => /^9[345][0-9]{3}$/

# find students with invalid characters in their names (old style finder)
Student.all :conditions => { :name => /[^a-zA-Z ]/ }

# find products with a complex code structure (dynamic finders)
Product.find_by_code /^[NRW][^-]+-[456]/

Be Aware

POSIX Only (mostly)

Most DBs only support POSIX regexps!

Let me repeat? POSIX only! So, some examples of things to know:

  • ^ and $ have their POSIX meanings, so beginning and end of the whole string, not of each line within the string. Also \A and \Z have no special meaning.
  • Convenience character classes like \w \W \d \D \s \S
  • Capturing parens won't break the RE, but there's no capturing (so you can't use what you captured)
  • No extended patterns, so (?i:foo) won't work, nor will (?:bar) and nor will (?i)foo
  • No look-around assertions work, so no foo(?!bar)

SQLite is very slow

SQLite's implementation of REGEXP is actually a callback to a user defined function, which this gem provides in Ruby. This is really cool™ because SQLite users get to use full Ruby regexps (ie. none of the limitations above apply) but it comes at a cost.

On a relatively small data set (say 1000 rows) my MySQL testing ran through all records in 2.3ms whereas SQLite took 84.6ms (because it has to call out to Ruby for each row tested).

So, don't be surprised if SQLite falls in a heap, and I'd recommend just abandoning this idea for any production usage.

Only SQLite, MySQL and PostgreSQL supported out of the box

You can add your own support for any other DB that supports regexp. I know that Oracle has a regexp function, and I believe that MSSQL has a regexp XP (a Perl RE one actually).

Here's how I'd add in Oracle support:

# config/initializers/wherex.rb
module Wherex
  module OracleEnhancedAdapter
    def regexp left, right
      "REGEXP_LIKE( #{left}, #{right} )"

    def regexp_not left, right
      "NOT #{regexp left, right}"

That's it (and the 'NOT' is only necessary if you use meta_where or something that enables negative Arel statements to be generated). You just have to make sure it is named correctly (needs to be the same as your actual adapter, so if you're using SomeOtherOracleAdapter then you need to name your module that too).

Wherex will pick this module up, and add it into the right place. Just see lib/wherex/adapters.rb for more examples.


With the latest 1.1 I have added Appraisal for testing multiple versions of ActiveRecord. Check that out for how it works, but basically you can run tests for all supported AR versions with:

appraisal rake

or you can pick one of the names from the Appraisals file and run just one, eg:

appraisal ar-4.0 rake


There are test suites for all three database engines that ship with Rails, the default is SQLite and requires no preconfiguration. So you can just clone the repo and run rake and it will run the tests against SQLite

If you want to run the tests against MySQL or PostgreSQL then you will first need to create a wherex_test database in your local machine for the given DB. Then you will need to bundle install for the given DB by using the DB environment variable, eg:

DB=mysql bundle


DB=postgres bundle

You do the same thing when you're running the tests, eg:

DB=mysql rake


DB=postgres rake

These will use a default user of root for MySQL and postgres for PostgreSQL. If you want to use different usernames or passwords then take a look in the config/database.yml file and either provide the appropriate environment variables, or edit the file itself.

You can also run an appraisal, or all appraisals through the same thing:

DB=mysql appraisal rake


Copyright © 2014 Jason King. See LICENSE.txt for further details.