Rails 5: form_for vs form_with

Question

Rails 5 has introduced new form helper method form_with.

How does it differs with form_for and when is it more appropriate to use?

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Answer 1

This is really in preparation for rails 5.1 where only form_with should be used. It's meant to serve as a replacement for the two methods form_for and form_tag.

form_for and form_tag in Rails were very similar, both allowed you to create a form tag but the first one uses model’s attributes to build create or update form, while the second one simply creates an HTML form tag with the passed URL as action.

Breakage

could you add a link to that quote? I didn't see it mentioned in guides.rubyonrails.org. – Salaried

That's because it's not a quote from rubyguides. :) I extracted that from the guides and just used blockquote for formatting. – Breakage

Note that now with form_with, your labels won't automatically link up to your inputs like they did previously with ids being automatically added. For a label to properly pair up to an input field (with the for attribute) you now need to explicitly add the id attribute to the input. – Crabbe

Answer 2

Use form_with (more up-to-date)

• form_with is the latest.
• form_for and form_tag are obsolete.

Why is there a change?

See Kasper Timm Hansen's pull request - I cannot state it better than pull request itself:

form_tag and form_for serve very similar use cases. This PR unifies that usage such that form_with can output just the opening form tag akin to form_tag and can just work with a url, for instance.

This means you don't need to use form_tag if you don't have a model. You can use the form_with helper and it can still handle URLs.

Note Re: Ids and Classes: The Ruby 5.1 version of form_with, by default doesn't attach a class or id to the form. For Rails 5.2 and later, however, form_with WILL automatically generate ids based on the model, if present—basically the same id behavior as form_for, so you will NOT need to manually specify them anymore. (source)

Housewifely

The last paragraph about default ids and classs is an important distinction! For a label to properly pair up to an input field (with the for attribute) you now need to explicitly add the id attribute to the input. – Crabbe

Answer 3

Existing answers are great. What I also found helpful were the first few paragraphs here. Basically:

form_tag and form_for are soft deprecated and they will be replaced by form_with in the future.

• DHH's proposal: https://github.com/rails/rails/issues/25197
• The pull request: https://github.com/rails/rails/pull/26976/files (I didn't read it, but it could be useful)

Quadrivial