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Perils of ORM caching

So, I was working a rails4 project today and added an after_create method to a model (call it model A) that checked on a related object (call it model B) to see its state, and if it met a certain criteria, did something to the model A object being created. The specifics don’t really matter, but I was using zeus to run my rpsec tests.

This caused three tests to fail in entirely unrelated sections of the application.

What on earth was going on?

Well, first I used git bisect to determine the exact commit that caused the issue.  (As far as I’m concerned, the existence of git bisect confirms my belief to ‘commit early, commit often’).

Then I dug in.  It appears that each of the tests was tweaking the model B object, and testing some aspect of the change, usually through the model A object.  Before I added the after_create method, the model B object wasn’t loaded into the ActiveRecord in memory network graph tied to the model A object when the test saved the model A object initially, but was loaded from the database when the method under test executed.

After the after_create method was added, the model B object was loaded into the in memory network graph tied to the model A object.  Then the test tweaked the model B object in the database, but didn’t reload the model A object, which had a dirty/old version of the model B object.

A simple reload of model A (and its network graph) fixed it (or a repositioning of when I modified the model B object), but it was quite a subtle testing bug to track down.

Rails Testing | moore | | Leave a comment

Adding a sitemap to sharetribe

map-1434486_640I have using the excellent Sharetribe framework to build a marketplace for food businesses and commercial kitchens for my new startup, The Food Corridor.  However, it didn’t have support for generating a sitemap.xml file for all the listings available.

How is someone going to find the right kitchen space when they use google, but we don’t have a sitemap so google can keep apprised of all the options?

This wouldn’t do.  So, I added the ability to generate a sitemap for all the listings in the marketplace.

First off, install the gem–I used sitemap_generator as it seemed to do what I needed–allow me to call out certain routes and add them to my sitemap.  Then you need to create a configuration file, at config/sitemap.rb.  Mine looks like:


SitemapGenerator::Sitemap.default_host = "https://"+APP_CONFIG.domain

SitemapGenerator::Sitemap.create do
  Listing.where(deleted: false, open: true).find_each do |listing|
    add listing_path(listing), :lastmod => listing.updated_at
  end
end

 

Then I just ran bundle exec rake sitemap:refresh:no_ping and a sitemap.xml.gz was generated in my public directory.

If you are running on AWS or someplace else with a persistent filesystem, you can skip to the text starting with “Then, I scheduled”.

If you are running on a PAAS like Heroku, where you don’t get a persistent filesystem, you’ll want to push this generated file to a persistent place. I chose S3. Since sharetribe already has paperclip as a dependency, I used the instructions here and here, with a few modifications for sharetribe.

My rake task to upload the sitemap file was:


require 'aws'
namespace :sitemap do
  desc 'Upload the sitemap files to S3'
  task upload_to_s3: :environment do
    s3 = AWS::S3.new(
      access_key_id: ENV['aws_access_key_id'],
      secret_access_key: ENV['aws_secret_access_key']
    )
    bucket = s3.buckets[ENV['s3_bucket_name']]
      file = File.join(Rails.root, "public", "sitemap.xml.gz")
      path = "sitemap/sitemap.xml.gz"

      begin
        object = bucket.objects[path]
        object.write(file: file)
        object.acl=(:public_read)
      rescue Exception => e
        raise e
      end
  end
end

I then run the sitemap:refresh:no_ping and upload_to_s3 tasks in the same heroku scheduled task: rake sitemap:refresh:no_ping sitemap:upload_to_s3. If you don’t do that (and instead do separate dynos) then the upload task won’t have access to the file (because it will have been generated on the first dyno’s filesystem).

You also need to make sure to add a sitemap controller to redirect from yourdomain.com/sitemap.xml.gz to the S3 bucket (again, as outlined in the articles linked above.

Then, I scheduled a daily refresh of the sitemap.xml file and submitted the file to relevant search engines.

Things I didn’t do:

  • handle more than 50k urls
  • support multiple communities (not really needed for me, but I bet if the folks behind sharetribe.com wanted to use this, they’d want such support).
  • add the sitemap.xml file to my robots.txt file, as outlined here.
Rails Sharetribe Useful Tools | moore | | Leave a comment

Review of Modular Rails

I am currently working on modifying an existing large rails app.  I am customizing some of the look and feel and extending functionality.

The app is under current development and I wanted to be able to take advantage of bug fixes or improvements, without impacting my customizations.  Or at least minimizing that impact.

Being fairly new to Rails, I surveyed the landscape and thought that building my customizations as an engine would be a good way to go.  (I was wrong, because engines have a hard time reaching out and modifying the application that they are part of.  At least that seemed to be a non standard use of engines from what I can find.) The author of Modular Rails has some good blog posts about engines and modularity, so I bought his book.

Pluses:

  • Good overview of how to extend three major components of rails app, models, views and controllers
  • Easy reading style
  • Leverages existing gems like deface
  • Mentions testing
  • Starts from first principles and then later gives you a gem to speed up development
  • Not too long
  • Information on setting up your own gems server

Minuses:

  • Focus on ‘greenfield’ apps.  No mention of integration with existing monoliths.
  • Uses nested modules, unlike every other engine article out there
  • Assumes relatively advanced knowledge of rails
  • Fair bit of fluff–lots of ‘mv’ commands
  • Extra charge for source code

All in all I am glad I read this book.  It didn’t fit my needs, but it didn’t promise that either.  I found it a good overview of the engine concept, even if he did do some things in a non standard manner and was a bit verbose about unix commands.

If you have done more Rails development, it will be more useful, and it is a great way to think about building new freestanding applications.  I haven’t surveyed the entire rails book landscape but I haven’t found anything out there focusing on Rails engines that is better.

Books Rails | moore | | Leave a comment