How can I check form input before submit?

Rails
1

I want to check user input in a form before submit. Is there a standard
way to do this in Rails?

2

You will want to use validation checks.

http://guides.rubyonrails.org/activerecord_validations_callbacks.html

3

Älphä Blüë wrote:

You will want to use validation checks.

http://guides.rubyonrails.org/activerecord_validations_callbacks.html

This is the Active Record validation. I am looking for something like
Action Controller validation( I am not sure whether rails has this
feature). I want to validate the user input in the web form when user
clicks sumbit button.

4

So, the first question you have to answer is what type of form are you
using? If you are using a form_for then that’s backed by a model and
you can use validation checks. If you are using form_tag then that
isn’t backed by a model and there are other ways of checking, depending
on what you are using.

Example: I have a form_tag that works with an ajax widget so I can
actually create a validation method using javascript and call the
validation on submit.

5

Zhao Yi wrote:
[…]

This is the Active Record validation. I am looking for something like
Action Controller validation( I am not sure whether rails has this
feature). I want to validate the user input in the web form when user
clicks sumbit button.

If you set up the validations in the model, Rails will validate form
submissions just as you are describing. Try it!

Best,

Marnen Laibow-Koser
http://www.marnen.org
removed_email_address@domain.invalid

6

Älphä Blüë wrote:

So, the first question you have to answer is what type of form are you
using? If you are using a form_for then that’s backed by a model and
you can use validation checks. If you are using form_tag then that
isn’t backed by a model and there are other ways of checking, depending
on what you are using.

Example: I have a form_tag that works with an ajax widget so I can
actually create a validation method using javascript and call the
validation on submit.

I use form_tag. How can I do the validation? Do you mean I have to write
it in javascript? Does Rails have a validation helper on this?

thanks.

7

I think I might have found a fix for your issue:

http://www.hackido.com/2009/06/validating-formtag-in-activerecord.html

8

Hey mate, so I wish I could give you a lot of advice on this but I’m
getting my feet wet on similar issues. :slight_smile:

The best practices you should remember is that you use form_for when you
are doing inserting of rows or data (create/edit) etc. and form_tag is
just for creating normal forms.

Because it doesn’t have a model, from my understanding you have to call
a validation method either one of two ways:

  1. with a validation check via javascript like so:

<% form_tag your_controller_path, :method => ‘get’, :onsubmit => ‘return
validate(this)’ do %>
form…
<% end %>

The validate() would be a javascript validation method that would return
true or false depending on the criteria you are testing.

  1. you could also use the config/initializers folder to write your ruby
    code as helpers and apply code that will disable the submit button until
    the conditions are properly met or something similar. Here’s a good
    example of that:

http://www.webficient.com/2008/10/18/easy-rails-patching

However, as always (when someone like me who is also new) answers
questions, someone with a lot more experience with rails might come
along and teach us both something new. :slight_smile:

Marnen is a really good expert and has helped me out a ton in the past.
If he says you can do the validation checks in the model, it might
possibly be that you can. I haven’t found a way to pass the validation
checks to the model without using a form_for tag though…

9

Zhao Yi wrote:
[…]

I use form_tag. How can I do the validation?

The easiest way would be to use form_for, in which case Rails will do
the validation automatically. I’m not sure if there’s an automatic
method with form_tag.

Best,

Marnen Laibow-Koser
http://www.marnen.org
removed_email_address@domain.invalid

10

OK, I understand. Thanks all your help.

11

If what you want is to validate the form on the browser you’ll need
Javascript. In any case you’ll need to also validate it in the server
because anybody can fake a page with appropriate modifications to try
and hack your app., completely bypassing any validations you might put
in place with Javascript.

Pepe