Is there a clean way to avoid calling a method on

Question

This question already has answers here:

How to avoid NoMethodError for missing elements in nested hashes, without repeated nil checks? (17 answers)

Closed 4 years ago.

I'm interested in getting the nested 'name' parameter of a params hash. Calling something like

params[:subject][:name]

throws an error when params[:subject] is empty. To avoid this error I usually write something like this:

if params[:subject] && params[:subject][:name]

Is there a cleaner way to implement this?

Answer 1

Not really. You can try fetch or try (from ActiveSupport) but it's not much cleaner than what you already have.

More info here:

• Nested hash defined?()

UPDATE: Forgot about andand:

• http://andand.rubyforge.org/

andand lets you do:

params[:user].andand[:name] # nil guard is built-in

Similarly, you can use maybe from the Ick library per the answer above.

Answer 2

When I have same problem in coding, I sometimes use `rescue'.

name = params[:subject][:name] rescue ""
# => ""

This is not good manners, but I think it is simple way.

EDIT: I don't use this way often anymore. I recommend try or fetch.

Answer 3

I wrote Dottie for just this use case — reaching deep into a hash without first knowing whether the entire expected tree exists. The syntax is more succinct than using try (Rails) or maybe (Ick). For example:

# in a Rails request, assuming `params` contains:
{ 'person' => { 'email' => '[e-mail]' } } # there is no 'subject'

# standard hash access (symbols will work here
# because params is a HashWithIndifferentAccess)
params[:person][:email] # => '[e-mail]'
params[:subject][:name] # undefined method `[]' for nil:NilClass

# with Dottie
Dottie(params)['person.email'] # => '[e-mail]'
Dottie(params)['subject.name'] # => nil

# with Dottie's optional class extensions loaded, this is even easier
dp = params.dottie
dp['person.email'] # => '[e-mail]'
dp['subject.name'] # => nil
dp['some.other.deeply.nested.key'] # => nil

Check out the docs if you want to see more: https://github.com/nickpearson/dottie

Answer 4

Check Ick's maybe. You don't need to significantly refactor your code, just intersperse maybe proxies when necessary:

params[:subject].maybe[:name]

The same author (raganwald) also wrote andand, with the same idea.

Answer 5

You can avoid the double hash access with an inline assignment:

my_param = subj_params = params[:subject] && subj_params[:name]

Answer 6

I cross posted this from my answer over here:

How to check if params[:some][:field] is nil?

I have been looking for a better solution too.

So I figured let's use try a different way to test for a nested key being set:

params[:some].try(:has_key?, :field)

It's not bad. You get nil vs. false if it's not set. You also get true if the param is set to nil.