If string is empty then return some default value

Question

Often I need to check if some value is blank and write that "No data present" like that:

@user.address.blank? ? "We don't know user's address" : @user.address

And when we have got about 20-30 fields that we need to process this way it becomes ugly.

What I've made is extended String class with or method

class String
  def or(what)
    self.strip.blank? ? what : self
  end
end

@user.address.or("We don't know user's address")

Now it is looking better. But it is still raw and rough

How it would be better to solve my problem. Maybe it would be better to extend ActiveSupport class or use helper method or mixins or anything else. What ruby idealogy, your experience and best practices can tell to me.

David Phillips · Accepted Answer · 2011-02-02 05:59:03Z

260

ActiveSupport adds a presence method to all objects that returns its receiver if present? (the opposite of blank?), and nil otherwise.

Example:

host = config[:host].presence || 'localhost'

edited Feb 2, 2011 at 5:59

answered Jan 27, 2011 at 19:24

David Phillips

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2 Comments

fl00r Over a year ago

this is cool. Default rails posibilities are preffered. Thanx!

fl00r Over a year ago

Firstly it is preffered because in my solution I should extend String, Fixnum and NilClass at least. And here I can just use clear code without bycles

Matt Briggs · Accepted Answer · 2011-01-27 14:25:13Z

12

Phrogz sort of gave me the idea in PofMagicfingers comment, but what about overriding | instead?

class String
  def |(what)
    self.strip.blank? ? what : self
  end
end

@user.address | "We don't know user's address"

answered Jan 27, 2011 at 14:25

Matt Briggs

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Comments

Phrogz · Accepted Answer · 2011-01-27 14:21:23Z

2

Since you're doing this in Ruby on Rails, it looks like you're working with a model. If you wanted a reasonable default value everywhere in your app, you could (for example) override the address method for your User model.

I don't know ActiveRecord well enough to provide good code for this; in Sequel it would be something like:

class User < Sequel::Model
  def address        
    if (val=self[:address]).empty?
      "We don't know user's address"
    else
      val
    end
  end
end

...but for the example above this seems like you'd be mixing view logic into your model, which is not a good idea.

answered Jan 27, 2011 at 14:21

Phrogz

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1 Comment

fl00r Over a year ago

Yes, it is bad idea to set defaults in models :) My forms will weep

Tonttu · Accepted Answer · 2011-01-27 14:31:37Z

2

Your or method might have some unwanted side-effects, since the alternative (default) value is always evaluated, even if the string is not empty.

For example

@user.address.or User.make_a_long_and_painful_SQL_query_here

would make extra work even if address is not empty. Maybe you could update that a bit (sorry about confusing one-liner, trying to keep it short):

class String
  def or what = ""
    self.strip.empty? ? block_given? ? yield : what : self
  end
end

@user.address.or "We don't know user's address"
@user.address.or { User.make_a_long_and_painful_SQL_query_here }

answered Jan 27, 2011 at 14:31

Tonttu

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2 Comments

fl00r Over a year ago

good remark. Got it. But why all code will be executed? look: a=2 ; a == 2 ? "ok" : @b = 3 ; @b; #=> nil

Tonttu Over a year ago

It will be executed when making the original call, not with the ternary operator. All the arguments will be evaluated on method call.

maxl0rd · Accepted Answer · 2011-01-27 19:49:06Z

1

It is probably better to extend ActiveRecord or individual models instead of String.

In your view, you might prefer a more explicit pattern like

@user.attr_or_default :address, "We don't know the user's address"

answered Jan 27, 2011 at 19:49

maxl0rd

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1 Comment

cabe56 Over a year ago

Is this part of Active Record? Did not find any references.

Lucio · Accepted Answer · 2019-02-23 20:43:20Z

0

Ruby:

unless my_str.empty? then my_str else 'default' end

RoR:

unless my_str.blank? then my_str else 'default' end

answered Feb 23, 2019 at 20:43

Lucio

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Comments

93sauu · Accepted Answer · 2023-02-13 15:08:08Z

0

I recommend to use options.fetch(:myOption, defaultValue) because it works great with boolean flags like the ones mentioned above and therefore seems better to use in general.

Examples

value = {}

puts !!(value.fetch(:condition, true)) # Print true

value = {}
value[:condition] = false

puts !!(value.fetch(:condition, true)) # Print false

value = {}
value[:condition] = true

puts !!(value.fetch(:condition, true)) # Print true

value = {}
value[:condition] = nil

puts !!(value.fetch(:condition, true)) # Print false

answered Feb 13, 2023 at 15:08

93sauu

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