ruby 2.1.1
Is there a way to do the logic in this piece of code in one line or a more concise manner?
user = User.new
h = Hash.new
attrs = [:name, :foo, :bar]
attrs.each do |a|
h[a] = user[a] if user.has_attribute? a
end
return h
3 Answers
If you're using Rails and User is an ActiveRecord model (which it looks like given your use of has_attribute?) then this will do the same thing:
user = User.new
...
return user.attributes.slice("name", "foo", "bar")
Or, if you really want symbols:
return user.attributes.with_indifferent_access.slice(:name, :foo, :bar)
3 Comments
Arup Rakshit
Your answer is compact one liner.. But just remove return, It is not need.
gwcoffey
I left the
return there to make it clear to the asker that this is the final result, in place of what he was returning before. Nothing wrong with a return if it adds clarity. :)gwcoffey
I concede… I just like my returns :)
It seems you are on Rails. If so,then -
attrs = [:name, :foo, :bar]
# the result hash will be returned, if last line of the method.
user.attributes.extract!(*attrs)
Look these methods extract! and attributes.
Example :
arup@linux-wzza:~/Rails/app> rails c
Loading development environment (Rails 4.1.1)
2.0.0-p451 :001 > h = { a: 1, b: 2, c: 3, d: 4 }
=> {:a=>1, :b=>2, :c=>3, :d=>4}
2.0.0-p451 :002 > h.extract!(:a ,:b ,:x)
=> {:a=>1, :b=>2}
2.0.0-p451 :003 >
Comments
Answers above are correct in Rails scope, I'l just add generic solution:
# assuming user[a] returns nil, if user have no a attribute
[:name, :foo, :bar].
map{|a| [attr, user[a]]}.
reject{|k, v| v.nil?}.
to_h
# assuming user[a] can raise if not user.has_attribute?(a)
[:name, :foo, :bar].
map{|a| [attr, user.has_attribute?(a) && user[a]]}.
reject{|k, v| !v}.
to_h
I've formatted them as NOT one-liners, but they are still one-statements :)
Basically, the trick is "invent the right method chain to convert one sequence to other", and requires to know all Enumerable sequence-transforming methods (map/select/reduce/reject/...), as well as a method to transform array of key-value pairs into hash (#to_h is standard in Ruby 2.1.1)
Hash.newwith no options is almost always written as simply{ }. It's also unnecessary to usereturn rwhenrat the end of the method has exactly the same effect. The only placereturnis normally used is to break out of a method early.Rails 4.1.1