Question

I have a hash which looks like this:

items:
    item:
        attribute_a: cheese
        attribute_b: bacon
    item:
        attribute_a: salmon
    item:
        attribute_a: mushrooms
        attribute_b: steak

I would like to get the value of attribute_b, I’m using the following:

if (result['attribute_b'])
  // do something
end

However if attribute_b is missing, I get an error:

The Identifier specified does not exist, undefined method '[] for nil:NilClass'

What is the (best) correct way to check if attribute_b exists?

Answer 1

It looks as if you’re getting the error not upon accessing the attribute 'attribute_b', but because result is nil.

The Identifier specified does not exist, undefined method [] for nil:NilClass`

It’s saying you’re calling the method [] on a nil value. The only thing you’re calling ‘[]‘ on is result.

The way you’re accessing 'attribute_b' is acceptable in general — I might be more specific and say:

if (result && result.has_key? 'attribute_b')
 // do something
end

This will make sure that result exists as well as making sure the attribute is not null.