Some of the most common methods I use on a daily basis when writing if/else’s and guard clauses are ‘presence checkers’. It can be really helpful to know if the Array, String, object etc. has is not just ’empty’/[]/false/nilas your existing logic may fail if passed such data. However Ruby (and Rails) have a number of methods to achieve this and as a junior dev I often found myself checking which to use in each specific scenario.

nil? blank? empty? which one to use?

The methods I come back to the most are blank? and present? (which is actualy just an alias for !blank?) because they offer an extra layer of safety in their return:

Either way you are guarenteed a true or false response and can build your logic around that boolean. Other methods are more restrictive:

• nil? will only return true when passed nil any other value results in false which restricts its usefulness to certain situations.

• empty? can only be used on Enumerables that is Hash’s ({}) and Array’s ([]) and String’s (" "), trying to use it on an Integer will result in:

=> 0.empty?
NoMethodError: undefined method `empty?' for 0:Integer

• There is even zero? which is restricted to just Integers and responds true on 0 and false on any other number.

• Rails, more specifically ActiveRecord offers exists? which when used against an ActiveModel::Model can be used for checking the DB for the existance of a model that matches the parameters passed:

# For a given model of 'Dog'
    Dog.exists?(5) # Checks for the ID of the model in the DB
    Dog.exists?('5') # See above
    Dog.exists?(['name LIKE ?', "%#{query}%"]) # Specify other attributes to query for
    Dog.exists?(name: 'Good Boy') # See above
    Dog.exists?(id: [1, 4, 8]) # Check multiple IDs at once
    Dog.exists?(false) # Return False
    Dog.exists? # Checks if there are any instances of Dog in the DB
    Dog.where(name: 'Skye', good_boy: true).exists? # More specific querying is possible

Further reading on exists?

Performance and presence checking

Unless you are Twitter scale it doesn’t matter.

Of course there are differences between using the different methods against different data types (as can be seen here in this comprehensive SO answer). However for most projects these presence checks will not be a performance bottle neck.

For example my favoured blank? is actually 2x slower than using empty?, this can easily be seen by looking at the source code:

def blank?
  respond_to?(:empty?) ? !!empty? : !self
end

However in most projects this performance hit will not be noticable.

One caveat to the above statement is when dealing with ActiveRecord checks which hit the DB. The topic of performance in those queries is quite involved and is expertly handled in this post which I would encourage anyone interested to read.

Thats all folks

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