One feature i’d like to expand upon is the ability to call raw SQL functions from Sequel’s DSL.

Here’s a migration where I create a speeches table with some full-text search columns:

Sequel.migration do
  up do
    create_table :speeches do
      primary_key :id
      String :text
      String :speaker
      Integer :year
    end

    run "ALTER TABLE speeches ADD COLUMN ts_text tsvector;"
    run "CREATE INDEX ts_text_idx ON speeches USING gin(ts_text);"
    run "CREATE TRIGGER tsvectorupdate BEFORE INSERT OR UPDATE
         ON speeches FOR EACH ROW EXECUTE PROCEDURE
         tsvector_update_trigger(ts_text, 'pg_catalog.english', text, speaker);"
  end
end

And here’s some sample code to query it:

require 'sequel'

def search(dataset, term)
  results = dataset.select do
    [ts_headline('english',
                 :text,
                 to_tsquery('english', term),
                 'MaxFragments=2').as(headline),
     id,
     speaker]
  end
  results.filter("ts_text @@ to_tsquery('english', ?::text)", term)
end

DB = Sequel.connect('postgres://localhost/blogpost')

DB[:speeches].insert(:year => 1865, :speaker => 'President Lincoln', :text => 'Fourscore and seven years ago')
DB[:speeches].insert(:year => 1963, :speaker => 'President Kennedy', :text => 'I am a Jelly Donut')

p search(DB[:speeches], 'President').all # returns both speeches
p search(DB[:speeches].where("year > ?", 1900), 'President').all # returns only the Kennedy speech

The search function takes in a dataset and a query term, and returns a new dataset filtered with a body or speaker name matching the query term,
as well as a “headline”, or the context around the search term to display in search results. This takes full advantage of a full-text search index.

Sequel is also great as glue code for calling PostGIS functions. I’ve found it especially useful for DRY-ing up long sets of raw SQL queries into maintainable scripts.

The post Access your database’s best features with Sequel appeared first on Pivotal Labs.

The client wanted to be able to see both the current status, and a history of all the statuses each object has been in.

These two requirements felt very closely tied, to the point where really the status is just the most recent action.

This could be fairly easily modelled in a Rails application as such.

class Rocket < ActiveRecord::Base
  has_many :activities, class_name: "RocketActivity"

  def current_activity
    activities.order("created_at DESC").first
  end
end

rocket.activities.map(&:status) # [landed, landing, cruising, launch, landed]
rocket.current_activity.status # landed

This seems like a fairly typical solution, and would provide you with a fairly easy to use accessor.

rocket.current_activity.status

But what if you wanted to view all the current activities of all the rockets you have in your fleet.

@rockets.each do |rocket|
  rocket.current_activity.status
end

Works great, but creates an n+1 problem, where every line is executing a query to find all the activities and return the latest.

A solution to this is to use includes, you could define rockets as

@rockets = Rocket.scope.includes(:activities)

Still, your custom logic inside the #current_activity method is then going to have to perform more sql on that collection.

Also it shouldn’t be the Rocket’s responsibility to know how to find it’s most recent activity, that’s more of a class concern.

Given that, in Rails land as long as you had a class to take care of it, you could define that relationship as.

class Rocket < ActiveRecord::Base
  has_many :activities, class_name: "RocketActivity"
  has_one :current_activity, class_name: "RocketCurrentActivity"
end

Leaving us to include the current_activity and output more efficiently.

@rockets = Rocket.scope.includes(:current_activity)

And keep our view the same.

@rockets.each do |rocket|
  rocket.current_activity.status
end

We solved this with SQL views (Wikipedia), and next week I’m going to show you how.

The post Rails and SQL Views – Part 1 appeared first on Pivotal Labs.

undefined method `fields' for nil

We keep getting this error across multiple projects & machines, with different versions of the pg gem and the PostgreSQL server, with varying consistency. Switching the tests to sqlite seems to fix it.

Failure/Error: Unable to find matching line from backtrace
ActiveRecord::StatementInvalid:
  NoMethodError: undefined method `fields' for nil:NilClass: SELECT "locations".* FROM "locations"  WHERE "locations"."id" IN (11, 10, 5, 4, 1, 3, 2)

It appears that PG::Connection#async_exec is returning nil for some queries.

It was suggested to add a "fields" method for the nil class.

Interestings

Homebrew is Kickstarting an automated test bot

http://www.kickstarter.com/projects/homebrew/brew-test-bot £50 to get a pair of pint glasses…

Resizing the window to test media queries

If you want to test your media query css as part of your acceptance suite, you can just ask Capybara to resize the firefox window.
Don't use the iframe to do this, because it will be buggy. Note you will need to use min/max-width not min/max-device-width when defining your media queries. Otherwise resizing the browser window will not trigger the media query.

Capybara.current_session.driver.browser.manage.window.resize_to(width, height)
Capybara.current_session.driver.browser.manage.window.position = Struct.new(:x, :y).new(session_name == :default ? 0 : width, 0)

Thanks to Ryan for the tip.

The post iFrame you frame… appeared first on Pivotal Labs.

• Rails 2.2.2 is released!

• Even Rails 2.2.2 isn’t always threadsafe. I found this out by running a script with JRuby from the command line. The script loaded the Rails environment and then launched two threads that simply tried to resolve an ActiveRecord class constant. Fireworks (in the form of LoadError) ensued deep inside of const_missing. I’ll post the full example later today.

• Tsearch2 is now built into Postgres (as of 8.3). This means you must remove the metadata from your tables, since Postgres now stores it in a separate place.

The post New York Standup 11/24/2008 appeared first on Pivotal Labs.