`try` method when trying to fetch hash value

Question

I'm trying to avoid an error message when pulling from a hash which may or may not have a value. I either want it to return the value or return nil.

I thought the try method would do it, but I'm still getting an error.

key not found: "en"

My hash is an hstore column called content... content['en'], etc.

content = {"es"=>"This is an amazing event!!!!!", "pl"=>"Gonna be crap!"}

Try method

@object.content.try(:fetch, 'en') # should return nil, but errors even with try method

I thought this would work but it doesn't. How else can I return a nil instead of an error?

Also, the content field itself might also be nil so calling content['en'] throws:

undefined method `content' for nil:NilClass

Answer 1

See the Hash#fetch

Returns a value from the hash for the given key. If the key can’t be found, there are several options: With no other arguments, it will raise an KeyError exception; if default is given, then that will be returned; if the optional code block is specified, then that will be run and its result returned.

h = { "a" => 100, "b" => 200 }
h.fetch("z")
# ~> -:17:in `fetch': key not found: "z" (KeyError)

So use:

h = { "a" => 100, "b" => 200 }
h.fetch("z",nil)
# => nil
h.fetch("a",nil)
# => 100

Answer 2

Just use normal indexing:

content['en'] #=> nil

Answer 3

As of Ruby 2.0, using try on a possibly nil hash is not neat. You can use NilClass#to_h. And for returning nil when there is no key, that is exactly what [] is for, as opposed to what fetch is for.

@object.content.to_h["en"]

Answer 4

If you need to allow for object.content.nil?, then you'd use try. If you want to allow for a missing key then you don't want fetch (as Priti notes), you want the normal [] method. Combining the two yields:

object.content.try(:[], 'en')

Observe:

> h = { :a => :b }
 => {:a=>:b} 
> h.try(:[], :a)
 => :b 
> h.try(:[], :c)
 => nil 
> h = nil
 => nil 
> h.try(:[], :a)
 => nil

You could also use object.content.try(:fetch, 'en', nil) if :[] looks like it is mocking you.