How to include a custom SQL function - ruby-on-rails

Question

I'm using find_by_sql to execute an SQL query.
I would like to be able to use Soundex and Levenshtein, but in order to use Levenshtein I need to include the function as a file.
This is my code so far:
info = params[:email].split('#')
name = info[0]
domain = info[1]
levenshtein = File.open("./lib/assets/mysql-function-levenshtein.sql")
results = Domain.find_by_sql(
"" + levenshtein + "
SELECT *
FROM domains
WHERE domain = '" + domain + "'"
)
I have no idea if simply including it in the query is even valid.
What's the best implementation?
By the way the file I'm trying to include is this:
https://github.com/vyper/levenshtein-sql

Answer 1

First off, I think you'd be better off just defining that function in your database with a migration, so you wouldn't have to define it again for every query where you want to use it:
class AddLevenShteinFunctionToDatabase < ActiveRecord::Migration
  def up
levenshtein = File.read("/path/to/levenshtein.sql")
    execute levenshtein
  end
def down
# maybe put some code here to delete the function
end
end
With this done, you could also add a scope to your Domain model for doing these kind of queries:
scope :levenshtein, lambda {|s1, s2| select("levenshein(#{s1}, #{s2})") }
With this, you should be able to write your queries something like this:
results = Domain.levenshtein("LEONARDO", "LEONARDU").where(:domain => domain)