如何在一行中编写条件语句？ 栏杆

Question

I am trying to say this

self.preferred_amount * object.each{|li|li.variant}.collect{|li|li.weight}

The only problem is that certain weights equal nil.

Being that the case, I would like to add that if they do equal nil, make them equal 0.

Is there any way to incorporate this logic in the same line?

Or is there a way I can make this statement even more refactored than it is?

Answer 1

Change li.weight to li.weight || 0 li.weight || 0

|| is the "short circuit or" operator. If its left hand side is truthy (neither false nor nil), it returns the left hand side, otherwise it returns the right hand side.

There is a feature in MRI >= 1.8.7 that will let you make this terser. Instead of:

each{|li|li.variant}

you can write

each(&:variant)

In versions of Ruby before 1.8.7, require the backports gem to get this feature.

Better than that, move all of the logic into object's class, eg

class Whatever
  def variant_weights
    each(&:variant).collect{ |li| li.weight || 0}
  end
end

and to use it:

self.preferred_amount * object.variant_weights

However, note that it is a bug to multiply a scalar amount by an array. If you mean to sum the weights, then:

class Whatever
  def total_variant_weights
    each(&:variant).collect{ |li| li.weight || 0}.inject(&:+)
  end
end

and to use it:

self.preferred_amount * object.total_variant_weights

Answer 2

Note, all the answers above are correct for your purpose, but to answer your question directly:

How do I write a conditional statement in a single line? Rails

You can use ternary operators. They take the following form:

assertion ? value_if_true : value_if_false
# if assertion is true, then value_if_true, otherwise, value_if_false

for example:

puts 4 < 5 ? 'you are on Earth' : 'you are on another planet'
<%= @user.is_admin? ? 'you can access this page' : 'you aren\'t allowed to be here' %>

Like I said, the answers above are actually what you want for this particular operation (not that a ternary operator won't work in this case). I just wanted to give you some more insight into one-liners.

Also note, this is not Ruby-specific. Most programming languages (including Ruby, PHP, CF, AS, JAVA, C, C#...) have ternary operators.

Answer 3

just || 0 || 0 the weight:

self.preferred_amount * object.each{|li|li.variant}.collect{|li|li.weight || 0}

Answer 4

尝试

 .collect{|li|li.weight || 0}

Answer 5

The each seems redundant. What about:

self.preferred_amount * object.collect { |o| o.variant.weight.to_i }

or if you really meant to sum the weights:

self.preferred_amount * object.inject { |sum, o| sum + o.variant.weight.to_i }