Phoenix – First Impressions

For the past decade, my primary tool for building web apps has been Ruby on Rails. Using such a toolset helps me rapidly build apps with a predictable structure and the means to manage the database schema.

Of course, there are trade-offs when such things are used, but discussing those is out of scope of this post. Instead, I hope to focus on some positives that they provide.

In my opinion, web frameworks show their worth in the early stages of app development and the mid term when there is some developer churn. It aids both Current Developer (present day maintainers) and Future Developer (eventual project maintainers) by providing some safe assumptions about where things are and the general app flow.

Enter Phoenix…

Recently, I began exploring Elixir and shared my first impressions [1]. Developing web apps in a manner similar to Rails naturally points to the Phoenix Framework, since the core team is influenced by it [2].

Rather than setting expectations for specific things, I jumped in with one thing in mind: hoping to find that I can remain as productive with Phoenix as I can with Rails.

How Did I Learn?

To get familiar with the framework, I followed the Phoenix guides provided on the main site. It hits all of the highlights for typical project management including resource generation, database management, and app testing.

Here are my take aways…

Thumbs Up!

A few of my favorite things…

Schema in the Model

In Active Record with Rails, details about the schema are “hidden knowledge” from the data model; the information is available in a separate database schema file. In Ecto, defining the schema inside the model exposes valuable information for Future Developer, providing the underlying makeup of the data model in line. Awesome!

Data Repo

Rather than executing any activity with the database directly through the data model, Ecto uses separate Repo modules to manage that activity. This is nice since it keeps the model isolated from database connectivity concerns, and instead leaves them focused strictly on data modeling.


Baked in support for channels allows any type of client to subscribe to Phoenix apps for “real time” data. With the BEAM managing large numbers of concurrent connections, the confidence level for a stable solution should be high.


This spec provides a good way to isolate behavior for reuse elsewhere that could be painless to test. Win!


Surprisingly, I encountered one thing that bothered me, but it is a big one.

Node.js Dependency

I was very disappointed to learn that I need Node.js for the default static asset manager, Brunch. To be fair, this dependency is optional, and any build tool can be used. However, from what I have seen, the default tends to be favored in the wild by frameworks.


Do I feel that I can be productive with Phoenix? Yes! I believe that after getting more comfortable with the tooling, and Elixir in general, that the development pace could be maintained.

Now I am eager to put it to work to see it in action!


  1. Elixir – First Impressions
  2. Phoenix is not Rails
Phoenix – First Impressions

Getting to know Ruby debugger

A key step to debugging any program is replicating the environment to ensure you can consistently produce the bug. In my early Ruby days, to inspect the environment, I used a primitive method: placing puts lines in my code to print values to the console (let’s call them “inspection puts”). It may have looked something like this:

class Buggy
  # assuming perform_operation and special_options exist...
  def buggy_method(param=nil, options={})
    puts "\n\n\nDEBUG"
    puts "param: #{param}"
    puts "options: #{options}"
    @instance_var = perform_operation(
      special_options(param, options)

The case for ruby-debug

This method very easily gives me the information I need, but it has some downsides:

  1. To inspect the return value of special_options I have to add another inspection puts.
  2. Every addition of a new puts requires that I restart the application to inspect the results.
  3. To inspect how special_options and perform_operation are handling the data, I have to add inspection puts inside of them.
  4. I must remember to remove all of the inspection puts before I push the code.

If only there was a better way to do this.

ruby-debug to the rescue! By putting a breakpoint in our code, we have the ability to inspect environment state, check the return value of any methods, and step through our code one line at a time. This is much more versatile than inspection puts because the full environment is available to us. The “I wonder what the value of this is” problem is gone since we can inspect whatever we want. The step functionality the debugger gives us is useful as well, allowing us to step inside of a called method while maintaining the interactive environment.

Setting up ruby-debug

To get set up with the debugger, we’ll need to install the gem:

# Using MRI-1.9.2
gem install ruby-debug19

# Using MRI-1.8.7 or Ruby Enterprise Edition
gem install ruby-debug

ruby-debug in action

Let’s update the example from above using a debugger breakpoint instead of inspection puts:

class Buggy
  # assuming perform_operation and special_options exist...
  def buggy_method(param=nil, options={})
    require 'ruby-debug'; debugger
    @instance_var = perform_operation(
      special_options(param, options)

The next time the method is called, the debugger will stop and give us an interactive shell. We can inspect the values of each variable with the eval command:

eval param
eval options

We can also see what the return value is of the invoked methods:

eval special_options(param, options)
eval perform_operation(special_options(param, options))

We can even use the step command to enter inside of special_options and perform_operation to see what they do.

Here are the various debugger commands that I most commonly use:

  • list, l – show the code for the current breakpoint
  • eval, e – evaluate expression and print the value
  • step, s – next line of code, moving within methods
  • continue, c – continue in the program until the program ends or reaches another breakpoint
  • quit, q – abort the program

Many more commands are available, which can be seen by entering help in the debugger.

Better debugging ftw!

With the ruby-debug gem, we have a better tool for diving in to our code than inspection puts. Using a debugger breakpoint, we can interactively step through our code with less cleanup.

Happy debugging!

Debugging references

Getting to know Ruby debugger