Rails single line if else statement

Question

I'm trying to write a single line if else statement in a view.

<%= collection.name ? collection.name : @miniature.name %>

I want it to put collection.name if one exists, otherwise I want it to put @miniature.name

What's wrong with the code you provided? – Marek Lipka Mar 26 '14 at 15:11 — Marek Lipka, Mar 26 '14 at 15:11

Marek Lipka · Accepted Answer · 2014-03-26T15:28:43.150

32

To make it even clearer, you can use logical OR and ActiveSupport's Object#presence (to put collection.name only if it exists and isn't blank):

<%= collection.name.presence || @miniature.name %>

If you want to display collection.name if it's not nil, but it's blank (empty string or string containing only whitespace), it will be enough to have:

<%= collection.name || @miniature.name %>

edited Mar 26 '14 at 15:28

answered Mar 26 '14 at 15:09

Marek Lipka

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This seems a very elegant way of doing it. I didn't realise you could use presence like that. – Ossie Mar 26 '14 at 15:13
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@WorldOfProper you can, because in case object is blank, `presence` returns `nil`, which is treated like `false` in any logical statements. – Marek Lipka Mar 26 '14 at 15:13
What was that downvote for? Please give explanation. – Marek Lipka Apr 01 '14 at 09:22

davegson · Answer 2 · 2014-03-26T15:47:36.947

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Check for the presence of collection.name first.

<%= collection.name.present? ? collection.name : @miniature.name %>

edited Mar 26 '14 at 15:47

answered Mar 26 '14 at 15:10

davegson

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Ternary operator - http://stackoverflow.com/questions/1428708/remembering-the-ternary-operator-syntax – Richard Peck Mar 26 '14 at 15:19
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Yes I know - I just was referencing for the OP if he wanted to research – Richard Peck Mar 26 '14 at 15:20
`if nil` won't throw any error, it will behave exactly like `if false`. – Marek Lipka Mar 26 '14 at 15:43
Still, where do you expect this error to be thrown? – Marek Lipka Mar 26 '14 at 15:44
@TheChamp it's true, but here, `name` can't be 'undefined'. What's more, if it could, your solution wouldn't work, you would probably have to use `defined?`. – Marek Lipka Mar 26 '14 at 15:45

score 0 · Answer 3 · edited May 23 '17 at 11:54

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Couldn't you have

<%= collection.name ||= @minature.name %>

To those who downvoted - Set Ruby variable if it is not already defined

edited May 23 '17 at 11:54

Community

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answered Mar 26 '14 at 15:20

Richard Peck

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Sorry I was writing as a conversation - let me change – Richard Peck Mar 26 '14 at 15:21
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I don't understand. This won't do what OP expects (display `collection.name` or `@miniature.name`) but will do what OP doesn't expect (set `collection.name` to `@miniature.name` if `@collection.name` is `nil`). – Marek Lipka Mar 26 '14 at 15:23
I believe my answer provided a valid answer to the OP – Richard Peck Mar 26 '14 at 15:31
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Your edited answer is valid, but it still may be surprise to OP that it also SETS `collection.name` to `@miniature.name` if it's `nil`. OP didn't specify this in requirements. Of course, I know the meaning of `||=` syntax, but I think it's not relevant here. – Marek Lipka Mar 26 '14 at 15:32

Rails single line if else statement

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