What is the best way to check if an attribute exists and is set?

Question

I have a common view that lists two different models. The only difference is that when setting the link_to action, one of the models has a link attribute and the other doesn't. I want to check if the link attribute exists, and if it does, check if it's set. I have the following which works, but I was wondering if there was a better way.

%li
  - if @element.has_attribute?("link") && @element.link
    = link_to @element.title, @element.link
  - else
    = link_to @element.title, @element

score 38 · Accepted Answer · edited Oct 06 '13 at 19:26

38

You could use presence:

= link_to @element.title, (@element.link.presence || @element)

Or, if @element might not have link at all, you could use try:

= link_to @element.title, (@element.try(:link) || @element)

edited Oct 06 '13 at 19:26

user229044

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answered Oct 06 '13 at 18:17

ck3g

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ahnbizcad · Answer 2 · 2016-05-25T23:01:17.447

13

I believe you can just do @element.attribute? (e.g. @element.link?) (I suppose we could call it "magic attributes".)

This checks for

the attribute existing on the model
the value not being nil

Exactly what you want.

edited May 25 '16 at 23:01

answered Nov 16 '14 at 08:38

ahnbizcad

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score 9 · Answer 3 · answered Oct 06 '13 at 18:14

9

Try using the attributes hash. This hash will return a key => value mapping of all of an activerecord object's attributes.

if @element.attributes['link']
  # Here we are
else
  # default
end

answered Oct 06 '13 at 18:14

OneChillDude

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8

better yet: `@element.attributes.key?('link')` – rickyrickyrice Oct 06 '13 at 18:16

score 0 · Answer 4 · answered Oct 16 '21 at 15:41

0

%li
  = link_to @element.title, @element[:link] || @element

answered Oct 16 '21 at 15:41

askrynnikov

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While this code snippet may solve the question, [including an explanation](http://meta.stackexchange.com/questions/114762/explaining-entirely-code-based-answers) will help people understand the reasons for your code suggestion. – Gerhard Oct 18 '21 at 12:42
@Gerhard In my humble opinion, this is the shortest / prettiest version of the code from the question. It does not contain a single extra code symbol. – askrynnikov Oct 18 '21 at 13:17

Eric Norcross · Answer 5 · 2022-07-28T20:02:54.747

0

There is also key? which is useful when checking if a property exists on the object, but would otherwise return nil or false.

For example:

a = { b: [] }

a[:b].presence # nil
a.try(:b) # nil
a[:b].present? # false
a.respond_to?(:b) # false

a.key?(:b) # true

So in this case:

%li
  = link_to @element.title, (@element.key?(:link) ? @element.link : @element)

edited Jul 28 '22 at 20:02

answered Jul 28 '22 at 19:55

Eric Norcross

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What is the best way to check if an attribute exists and is set?

5 Answers5