1. deivid-rodriguez/byebug
Byebug is a fantastic debugger available for Ruby 2 (and presumably above). Drop
gem ‘byebug’
into your Rails app Gemfile and bundle install. In either your test run or your development run, write
byebug
on a single line of your app and voila. When you hit that line, you will drop into the debugger.
If you’re not developing a Rails app, you can include ‘byebug’ at the top of your Ruby file.
Full docs here.
2. pretty print (pp)
Pretty print is one of my favorite introspection weapons to help see variables more clearly.
pretty print, which you write as pp, prints out your object with each attribute on its own line. Take for example this Spree::Country object, shown here on the Rails console without pretty print
2.4.6 :010 > x
=> #<Spree::Country id: 232, iso_name: “UNITED STATES”, iso: “US”, iso3: “USA”, name: “United States”, numcode: 840, states_required: true, updated_at: “2019-05-19 17:16:07”, zipcode_required: true>
Now, with pretty print, the same object is conveniently displayed with each attribute as its own line. This is invaluably helpful when you have deep nesting of objects.
2.4.6 :009 > pp x
#<Spree::Country:0x00007fd8507ea358
id: 232,
iso_name: “UNITED STATES”,
iso: “US”,
iso3: “USA”,
name: “United States”,
numcode: 840,
states_required: true,
updated_at: Sun, 19 May 2019 17:16:07 UTC +00:00,
zipcode_required: true>
3. puts, .to_s, and inspect
OK, so we get a 3-in-1 here: When you call puts on an object, .to_s will be called and then output to your screen. So you should make your objects have a .to_s that is human readable, possibly even for use in, say, a drop-down menu or label.
def class Person
attr_accessor :first_name, :last_name
def to_s
“#{first_name} #{last_name}”
end
end
inspect, on the other hand, is specifically for developers. In this method, you would write out as much information as you the developer (or next developer) want to see, including the keys (ids) of your objects if those will be helpful:
def class Person
attr_accessor :first_name, :last_name
def inspect
“Person id: #{id} – first: #{first_name}; last: #{last_name}”
end
end
Your objects should have both .to_s and .inspect on them, and you can try these universally named Ruby methods on other people’s objects to examine them. A well-formed codebase implements them or has helpful output for both of these.
4. .to_yaml
Pretty print’s cousin is the .to_yaml method, which will take your object and convert it into yaml. Take for example this arbitrary object, which you will notice contains a :ghi key that has a nested object as its value:
2.4.6 :023 > x= {abc: 1, def: 4, ghi: {ye: 6, nm: 3}}
=> {:abc=>1, :def=>4, :ghi=>{:ye=>6, :nm=>3}}
2.4.6 :024 > x
=> {:abc=>1, :def=>4, :ghi=>{:ye=>6, :nm=>3}}
.to_yaml on its own will produce a string that will output with newline characters, like so:
2.4.6 :025 > x.to_yaml
=> “-\n:abc: 1\n:def: 4\n:ghi:\n :ye: 6\n :nm: 3\n”
To make this more useful, try puts along with .to_yaml
2.4.6 :026 > puts x.to_yaml
–
:abc: 1
:def: 4
:ghi:
:ye: 6
:nm: 3
5. x.method(:_____).source_location
(where :_____ is name of the method — as a symbol — you are trying to search for)
OK, so the ultimate secret weapon of Ruby debugging is this little-known method that will magically — and I mean magically — tell you where a method was defined. That’s right, I mean the actual line number itself.
2.2.5 :002 > a.method(:hello)
=> #<Method: Apple(Thingy)#hello>
2.2.5 :003 > a.method(:hello).source_location
=> [“/Users/jason/Projects/nokogiri-playground/app/models/thingy.rb”, 2]
Look, ma, take a peek into my hard drive and you would find that the hello method is actually defined on the file at the full path /Users/jason/Projects/nokogiri-playground/app/models/thingy.rb on line 2.
Like magic it works for Rails and Gem code too, and is invaluable when you are ready to dive into the APIs you are working with.
6. x.methods
By default this method will return a list of all of the methods on an object. Watch out because you’ll get all the methods on the ancestor chain too.
In older versions of Ruby, you could use this method to examine the instance methods that were defined on this class only (excluding the ancestors), but unfortunately this no longer works.
If you pass this method false, like so:
x.methods(false)
…things get more interesting: then you get only the class methods defined on this object’s class itself. (Remember in Ruby class methods are defined with self.)
7. brunofacca/active-record-query-trace
An excellent gem that’s still a non-optional workhorse in my development practice – especially when debugging a legacy codebase. This gem will display for ALL of your SQL queries where in your Ruby or Gem code the active record update commands are coming from.
Follow the instructions in the Gem to create an initialize file and set it up. My only tip here that adds to the docs is that you’ll want to set the number of lines:
ActiveRecordQueryTrace.lines = 10
I find that when debugging a problem in my own Rails app I want this set to a lower number (like 5 or 10) and when debugging a problem in Gem code or in Rails I need this at a much higher number (like 50 or 100).
8. flyerhzm/bullet
Understanding N+1 queries is a significant litmus test that sets amateurs from the professionals. Bullet is like a magic bullet – literally named so – for finding your N+1 queries.
Bullet is a great gem that you should install in either development or test, not in production. Often because it does add overhead to your speed, I install it but leave it configured so that it is turned off by default and any developer on the team who needs it can turn it on.
You CAN and SHOULD turn it on periodically too, to examine where your app is producing N+1 queries.
Here’s the catch with Bullet: Remember that Active Relation objects are created as chains of conditions before they get translated and executed as SQL. That’s why when you do this you must carefully consider
query = Country.where(name: “United States”)
When you do this in your Rails console, you will see it run the SQL right away.
2.4.6 :039 > Spree::Country.where(name: “United States”)
Spree::Country Load (0.7ms) SELECT `spree_countries`.* FROM `spree_countries` WHERE `spree_countries`.`name` = ‘United States’ LIMIT 11
It only does this because of the ‘print’ effect the Rails console has on your objects. If you string another .where onto this object, when translated into SQL, ActiveRecord will combine the queries:
query = Spree::Country.where(name: “United States”); query.where(iso: “US”);
Spree::Country Load (1.0ms) SELECT `spree_countries`.* FROM `spree_countries` WHERE `spree_countries`.`name` = ‘United States’ AND `spree_countries`.`iso` = ‘US’ LIMIT 11
The reason this is important is that to understand where your N+1 queries are coming from you need to understand when you are creating your Active Relation objects and when they are invoked. They are not the same place, although on the Rails console it makes you think it is one and the same. When you grok this, you will see why Active Record’s side loading (which loads a related set of objects in a single optimized query, taking the number of queries from N+1 to 1+1=2) is both efficient and can be tricky to work with, especially with objects that have many relationships.
Don’t be fooled: Side-loading is nearly always more efficient than N+1 queries.
Bullet tells you where those pesky N+1 queries are invoked, but not where you are creating them. What you then need to do is trace your code (manually) to figure out where the queries are being created, which hopefully should be near in the code to where they are being invoked ( but in the case of complex filtering logic might not be).
Here you need to add the appropriate .joins(:____) to your code anywhere between when the objects are set up and when they are invoked by Active Record. Note that you’ll only want to join in those additional tables if they are actually used. If not, you don’t need the over head.
You’ll know you’ve solved your N+1 queries because you won’t see them output in your Rails log, and they’ll disappear from the Bullet code.
9. better_errors
Since Rails 4 adopted a near identical default, this used to be more interesting. For a Rails 3 app it can bring your error crash console up to Rails 4 standards.
10. Introspect, Introspect, Introspect but remember Ruby’s last-line quirk
Always look at what you’re doing. Drop into your debugger, look at your variables, clone & freeze them, look for race conditions, look for flip-floppers, watch out for your own confirmation bias. Remember that when in the debugger or on the Rails console and you type a SINGLE VARIABLE and HIT RETURN, the console will interpret that action as-if you had called .inspect
2.2.5 :007 > a
=> #<Apple id: nil, created_at: nil, updated_at: nil>
2.2.5 :008 > a.inspect
=> “#<Apple id: nil, created_at: nil, updated_at: nil>”
In some cases, the act of inspection actually changes the object (like in the case of an Active Relation, in which case it invokes the query), so keep that in mind (we might call this the “observer effect” in software development.)
