Ruby on Rails: Delete multiple hash keys

Question

I often find myself writing this:

params.delete(:controller)  
params.delete(:action)  
params.delete(:other_key)  
redirect_to my_path(params)

The trail of deletes doesn't feel right and neither does:

[:controller, :action, :other_key].each do |k|
  params.delete(k)
end

Is there anything simpler and cleaner?

When I wrote that the second approach didn't feel right, I meant that given the richness of the Hash API, I suspected that there was some method or idiom already out there for this and a monkey patch wouldn't be necessary. Maybe not, though. Many thanks to all who answered! — Mark Westling, Oct 13 '09 at 15:08
Hash#except was exactly what I was looking for. I didn't remember that it's a Rails core extension so I was puzzled when I couldn't find it in the Hash API. — Mark Westling, Oct 13 '09 at 16:15
Note that strictly the answer is `Hash#except!` but `Hash#except` is the way to go (don't mess with `params`!). As a rule of thumb, don't mess with any object in-place unless absolutely required, the side-effects may be have unexpected results. — tokland, Aug 19 '13 at 11:36

score 234 · Accepted Answer · edited May 22 '14 at 14:51

234

I'm guessing you're unaware of the Hash#except method ActiveSupport adds to Hash.

It would allow your code to be simplified to:

redirect_to my_path(params.except(:controller, :action, :other_key))

Also, you wouldn't have to monkey patch, since the Rails team did it for you!

edited May 22 '14 at 14:51

Dominic Sayers

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answered Oct 13 '09 at 15:43

Ben Crouse

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Ahhh, I knew I'd seen this before but I couldn't remember where! (Hence my "this doesn't feel right" remark.) Thanks! – Mark Westling Oct 13 '09 at 16:10
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One of those lesser documented methods. I went looking for something like this while proposing an answer but didn't see it. – tadman Oct 13 '09 at 21:41
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For some reason except didn't work. But `except!` did. Rails 3.0 – Trip Aug 17 '12 at 16:53
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Rails 3.2 on ActiveRecord attributes, had to use strings for the keys? i.e. `User.attributes.except("id", "created_at", "updated_at")` symbols did not work – house9 Dec 18 '12 at 18:18
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Adding to what @house9 mentioned, ActiveRecord `attributes` method returns a `Hash` with keys that are `String`. So then you would have to use string key names in `.except()`. However I get around this using the `Hash.symbolize_keys` a la `@user.attributes.symbolize_keys.except(:password, :notes)` -- using `symbolize_keys` makes it work as one would expect – FireDragon Jan 08 '20 at 01:18

score 46 · Answer 2 · edited Oct 16 '20 at 00:03

46

While using Hash#except handles your problem, be aware that it introduces potential security issues. A good rule of thumb for handling any data from visitors is to use a whitelist approach. In this case, using Hash#slice instead.

params.slice!(:param_to_keep_1, :param_to_keep_2)
redirect_to my_path(params)

edited Oct 16 '20 at 00:03

Fralcon

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answered Oct 14 '09 at 19:57

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Thanks for mentioning the security issues surrounding redirection. – David J. Feb 04 '11 at 19:14
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Just a heads up: ActiveSupport, not Ruby itself, provides Hash#slice and #slice! http://as.rubyonrails.org/classes/ActiveSupport/CoreExtensions/Hash/Slice.html – David J. Feb 04 '11 at 19:34
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I couldn't get David James's link to work but this one seems to be ok: http://api.rubyonrails.org/classes/Hash.html#method-i-slice – Dominic Sayers May 22 '14 at 14:47
undefined method 'slice!' for `{:b=>2, :c=>3}:Hash` – Khurram Raza Apr 15 '19 at 08:35

score 28 · Answer 3 · answered Oct 13 '09 at 15:32

28

I'd be completely happy with the code you originally posted in your question.

[:controller, :action, :other_key].each { |k| params.delete(k) }

answered Oct 13 '09 at 15:32

Bob Aman

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without modifying `Hash` this is the best answer :+1: – Dan Bradbury Feb 01 '16 at 20:53
I've used this method but replaced params with the name of the hash and then it worked!! The hash gets mutated. – Pablo Feb 24 '19 at 18:28

Mike Seplowitz · Answer 4 · 2013-07-29T16:23:42.760

15

Another way to phrase dmathieu's answer might be

params.delete_if { |k,v| [:controller, :action, :other_key].include? k }

edited Jul 29 '13 at 16:23

answered Oct 13 '09 at 14:38

Mike Seplowitz

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score 7 · Answer 5 · edited Feb 18 '14 at 21:14

7

Fire up a monkey patch?

class Hash
  def delete_keys!(*keys)
    keys.flatten.each do |k|
      delete(k)
    end

    self
  end

  def delete_keys(*keys)
    _dup = dup
    keys.flatten.each do |k|
      _dup.delete(k)
    end

    _dup
  end
end

edited Feb 18 '14 at 21:14

MrYoshiji

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answered Oct 13 '09 at 14:31

tadman

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Monkey patches are a tool of last resort. – Bob Aman Oct 13 '09 at 15:29
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Monkey patches *that replace existing functions* are a tool of last resort. Monkey patches that add new functions are Ruby 101. – David Seiler Oct 13 '09 at 15:33
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Should be `delete(k)` instead of `delete(key)` – Vincent Dec 29 '10 at 02:26
For code maintenance the implementation of the non-destructive `delete_keys` should be simply `dup.delete_keys!(*keys)` – Phrogz Apr 20 '15 at 21:18
@Phrogz Defining one in terms of the other isn't always a bad idea, but it's just left here unrolled for clarity. – tadman Apr 21 '15 at 15:53

score 4 · Answer 6 · answered Aug 17 '21 at 19:39

Starting from Ruby 3.0, Hash#except is supported directly. This means we would not need activesupport to access Hash#except.

From documentation:

Hash#except(*keys) → hash

This method returns a new hash, which includes everything from the original hash except the given keys.

example:

h = { a: 100, b: 200, c: 300, d: 400 }
h.except(:a, :d) #=> {:b=>200, :c=>300}

Reference:

https://docs.ruby-lang.org/en/3.0.0/Hash.html#method-i-except

score 2 · Answer 7 · edited May 23 '17 at 10:31

2

I don't know what you think is wrong with your proposed solution. I suppose you want a delete_all method on Hash or something? If so, tadman's answer provides the solution. But frankly, for a one-off, I think your solution is extremely easy to follow. If you're using this frequently, you might want to wrap it up in a helper method.

edited May 23 '17 at 10:31

Community

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answered Oct 13 '09 at 14:35

Pesto

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Ruby on Rails: Delete multiple hash keys

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