Monday, May 26, 2014

seconds_until_end_of_day expires for Cache in Rails

A colleague of mine had to cache some html until the end of the day but found it difficult because cache expects expires_in which is relative. We cant pass an absolute :P

So we now have seconds_until_end_of_day in 4.0.2, but we use Rails 3 :(

But patching Time is simple

def seconds_until_end_of_day
  end_of_day.to_i - to_i

Tuesday, April 29, 2014

Observers and Migratios

The past day we created a model migration and then added an observer for the model after the migration. Surprisingly, the observer (now added in the application.rb file) was loaded first by environment which then checks for the model and tries to fire a DB query for columns.

This fails and therefore the migration does not go through.

So for future reference, always migrate first and then add the observer! 

Friday, March 28, 2014

Chuck Norris Hubot

I stumbedupon an API which spits out random Chuck Norris Jokes and I ended up writing a smal hubot for this :)

Try it out Chuck Norris Hubot

Monday, March 10, 2014

Caching Simple Navigation

Morale: Simple Navigation is not that simple

We, in our firm, have different types of user navigation for different types of users. We wanted the flexibility of creating our navigation from the backend(rails) so that there is just one file to maintain with all configurations. Simple Navigation works great in this aspect.

The configuration is complex, but is absolutely generic. We have a couple of navigations to start with, for the normal application and when a user visits the application via the iPad.

The navigation for the normal user takes more than 500ms to render. NOT GOOD! We decided on caching the html. For this we need to split the navigation yet again. With respect to logged in users. Therefore we now have 4 types of navigation, loggedout-normal, loggedin-normal, loggedout-iPad, loggedin-iPad.

We also had some badges on the navigation for unopened items. The next step was to remove these from the navigation file. We created a notifications controller and wrote a small javascript, which takes data from the json response of the show method of this controller, and updated the corresponding sections in the navigation.

Now came the hard part. Caching.

We need to define keys for the Caching itself first.

For a logged out normal user, this would be quite straight forward. Get the locale of the navigation bar. All the users with the same locale got the same navigation bar.

For logged out normal users it would be a little tricky. We have some user specific stuff in the navigation bar such as the username. Therefore, we need the user_id. The user could change his locale and this would trigger a change in the updated_on field on the Users table. This would mean that we need to include this in the key as well. We have a specific link for backend services if the user has admin privileges. For this we need to evaluate the roles of the user. An MD5 has been used to facilitate this.

We need to Cache the non highlighted navigation bar for sanity purposes. Then we plan to highlight the section according to the pages that are rendered. For this we could either create a javascript to add the correct classes or create a stylesheet which highlights the correct section on verification of the correct classes.

We decided to create a stylesheet for this. The stylesheet reads the configuration from the simple_navigation configuration and creates the correct CSS. The file is a LESS file. We extracted the styles to highlight the navigation items into some mixins and used these mixins inside our custom classes.

The next tough part is the sub navigation. While this problem still lurks, we are trying to get away from the sub navigation altogether.

While this post is clearly not technical and is conceptual, this might help some others trying to solve something similar to this.