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?
Change li.weight to 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, e.g.
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
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.
just || 0 the weight:
self.preferred_amount * object.each{|li|li.variant}.collect{|li|li.weight || 0}
Try
.collect{|li|li.weight || 0}
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 }
Related
I commonly need to use this kind of methods where I have to check if an object exists and if this object returns a specific value or a behavior. Is that a better way to write this code?
def set_current_theme
if current_tenant && current_tenant.has_custom_domain?
#theme = Theme.last || Theme.create
end
end
At a first glance, I would just add one conditional: if current_tenant.has_custom_domain? and that should be enough. But the result is generally that there is no such method (in this case has_custom_domain?) for nil class.
Shorter (and i think better) way is to use &. (it's shorthand for try!) like this.
if current_tenant&.has_custom_domain?
#theme = Theme.last || Theme.create
end
What does &. (ampersand dot) mean in Ruby?
I would suggest early return (so called guard clause) instead of :if statement, because you don't have :else clause:
def set_current_theme
return unless current_tenant&.has_custom_domain?
#theme = Theme.last || Theme.create
end
I'm passing a hash to this function that either a) has keys that are strings along with values that are ints OR b) it is an empty hash.
The point of the function is to return nil if the hash is empty and return the key associated with the lowest int.
def key_for_min_value(name_hash)
if name_hash == nil
return nil
else
lowest_value = nil
lowest_value_name = nil
name_hash.collect do |name, value|
if lowest_value > value
lowest_value = value
lowest_value_name = name
end
end
return lowest_value_name
end
end
The error I'm receiving is:
1) smallest hash value does not call the `#keys` method
Failure/Error: key_for_min_value(hash)
NoMethodError:
undefined method `>' for nil:NilClass`
You can't compare nil to anything using >, it's not allowed, so you either have to avoid that test or use tools like min_by to get the right value instead of this collect approach.
One way to make your unit test happy might be:
def key_for_min_value(name_hash)
return unless (name_hash)
name_hash.keys.min_by do |key|
name_hash[key]
end
end
Ruby leans very heavily on the Enumerable library, there's a tool in there for nearly every job, so when you have some free time have a look around there, lots of things to discover.
Now Ruby is very strict about comparisons, and in particular a nil value can't be "compared" (e.g. > or < and such) to other values. You'll need to populate that minimum with the first value by default, not nil, then the comparisons work out, but doing that completely is pretty ugly:
def key_for_min_value(name_hash)
return unless (name_hash)
min_key, min_value = name_hash.first
name_hash.each do |key, value|
next unless (value < min_value)
min_key = key
min_value = value
end
min_key
end
So that approach is really not worth it. Enumerable makes it way easier and as a bonus your intent is clear. One thing you'll come to appreciate is that in Ruby if your code looks like code then you're probably going about it the wrong way, over-complicating things.
Ruby is an unusually expressive language, and often there's a very minimal form to express just about anything.
I'm trying to substitute an expression unless the expression is one of two values.
def substitute_string (string)
string.gsub('abc', 'xyz') unless string == ('dabc' || 'eabc')
end
substitute_string('jjjjjabc')
=> 'jjjjjxyz'
substitute_string('dabc')
=> 'dabc'
substitute_string('eabc')
=> 'exyz'
I expected substitute_string('eabc') to return ('eabc') since I stated that in the unless block, which I passed two values.
I don't understand why this doesn't work, and what I can do to make 'eabc' return 'eabc'.
('dabc' || 'eabc') is a boolean expression that evaluates to true and returns 'dabc'.
Use two or's:
unless string == 'dabc' || string == 'eabc'
Or use =~ (regex pattern match)
unless string =~ /(dabc|eabc)/
Since you indicated you're using Rails, you can also use in? like this:
unless string.in? ['dabc', 'eabc']
It is because (1) 'dabc' || 'eabc' is equivalent to 'dabc', and nowhere in your code does 'eabc' appear in a meaningful way, and because (2) it only returns nil when the condition is met according to the way you used unless.
def substitute_string(string)
case string
when 'dabc', 'eabc' then string
else string.gsub('abc', 'xyz')
end
end
Apart from the fun of obscure technicalities about what is returned when and in what situations, I don't see a lot of merit in not being more explicit with the return. The very fact that this issue was brought and subsequently debated on SO is exactly why writing code (working code to be sure) in this obscure fashion will lead to confusion for developers interpreting this code, and leads to buggy software.
The only benefit I see to this is that it's on one line.
def substitute_string(string)
string.gsub('abc', 'xyz') unless ['dabc', 'eabc'].include?(string)
end
I personally would prefer the following as it makes it clear what your intentions are:
def substitute_string(string)
return string if ['dabc', 'eabc'].include?(string)
string.gsub('abc', 'xyz')
end
'dabc' || 'eabc' will always equal true since it just means condition or condition where condition is a string. Since a string is not nil or false it evaluates to true. You could check whether the string is in an array values instead:
def substitute_string(string)
string.gsub('abc', 'xyz') unless ['dabc', 'eabc'].include?(string)
end
Is there a way to make this situation more compact in rails views?
Eg I have haml
= object.count unless object.count ==0
I sort of don't like that has I'm repeating the function there, I would much rather have something like
= object.count unless ==0
Eg if I had more complex statements
= object.relations.where(attribute: "something").count unless zero?
I could split that into two lines say
- cnt = object.relations.where(attribute: "something").count
= cnt unless cnt==0
But for each situation I would have multiple lines, and storing a variable to use once sucks.
EDIT: just to elaborate I want to check if the number is 0, and if so not display anything. It looks nicer in the view that way.
UPDATE:
One of the answers made come up with a solution along these lines
class Object
def unless
self unless yield(self)
end
end
So I can call whatever object I have with a block eg. .unless{|c| c<1}
This lets me tack the conditionals on, and keeps it pretty clear what is going on :), bonus is as it's block driven I can use this on any object :P.
Thanks everyone :)
UPDATE EVEN MORE
Having |c| in the block sucked. So I looked up the api and changed it too
class Object
def unless(&block)
self unless instance_eval(&block)
end
end
So now I can use .count.unless{zero?} to accomplish this :P. Or if I have a complicated condition I can add that in with |c| etc.
If object is an array you can use object.empty? (or object.any? for the reverse case)
Just create a view helper:
def display_count_or_nothing(array)
array.count unless array.count == 0
end
In the view you can use it like this:
<%= display_count_or_nothing(array) %>
i think the following is nice and clear, although i hate the variable "object",
it would be much nicer if the name of the variable described the contents of the array (as plural)
= object.count unless object.empty?
If this is only about count, you can monkey patch Enumerable:
module Enumerable
def count_or_empty_string
self.any? ? self.count : ''
end
end
If object is an enumerable, you can do this:
= object.count_or_empty_string
This will return an "" if object.count == 0 else it will return an integer. So there is no need for unless or if in your HAML anymore.
Does Rails have a this like javascript/Jquery does?
Take this example:
User.find_by_email(params[:candidate][:email].present? ? (u = this.id) : (u = 'not here')
or:
if User.find_by_email(params[:candidate][:email].present?
a += 1
user = this
end
I'm aware that this code might be rewritten in more efficient ways in this case, but my question is about being able to use this. Does Ruby have something like this?
In the context of a class you use self.
In these cases though this code is not in User context so you have to make an assignment.
u = User.find_by_email(params[:candidate][:email])
user_name = u.any? ? u.name : 'not here'
I prefer .any? to .present? in this context as it reads better.
Ruby uses self to denote this. I am not quite sure if you need to use self for your problems.
First scenario can be rewritten as:
u = User.find_by_email(params[:candidate][:email]).try(:id) || 'not here'
Second scenario can be rewritten as:
user = User.find_by_email(params[:candidate][:email])
a += 1 if user.present?
I'm guessing the more idiomatic ruby approach for your case would be something like the following:
User.where("email in (?)", email_arr).each do |user|
a += 1
user.foo = bar
end
but it's hard to say without seeing the all code.