# Forms and ActiveRecord validation magic

**URL:** <https://www.ruby-forum.com/t/forms-and-activerecord-validation-magic/124117>\
**Category:** Rails\
**Created:** [December 25, 2007, 12:36am UTC](https://www.ruby-forum.com/t/forms-and-activerecord-validation-magic/124117 "2007-12-25T00:36:04Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![gamehack](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/a3d4f5/32.png) [@gamehack](https://www.ruby-forum.com/u/gamehack)\
**Post date:** [December 25, 2007, 12:36am UTC](https://www.ruby-forum.com/t/forms-and-activerecord-validation-magic/124117/1 "2007-12-25T00:36:04Z")

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Hi all,

I’ve been digging through the code which scaffold creates (Rails 2).  
What I’m am looking for is to determine how does error\_messages\_for  
and form\_for determine that ActiveRecord object is completely new and  
should be validated before the user has had a chance to input some  
data. Basically, the first time the new.html.erb template is run,  
error\_messages\_for does not detect any errors even though the object  
is newly created (in the controller’s new method) and does not  
validate. But if you then enter data into the input boxes and submit  
the form, highlights the validation errors. So the question is how  
does it work out when it is being called the first time and should not  
validate the inputs?

When I was testing, I put a modelObject.valid? call in the beginning  
of the template and that made it highlight errors even before you had  
a chance to input any data. So it seems that error\_messages\_for and  
form\_for detect this in some way. The question is how? I’ve been  
digging through the sources and couldn’t find anything.

Thanks,  
gamehack

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<div class="post-metadata">

**Author:** ![gamehack](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/a3d4f5/32.png) [@gamehack](https://www.ruby-forum.com/u/gamehack)\
**Post date:** [December 25, 2007, 12:51am UTC](https://www.ruby-forum.com/t/forms-and-activerecord-validation-magic/124117/2 "2007-12-25T00:51:17Z")

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This is because errors are only created after an explicit call to  
#valid?,  
#save, or #create.

When you do ARObject.new, nothing has been run and thus nothing has  
errored  
out.

Also, there’s a new\_record? flag set to true.

Next time you do #save or #valid?, yaml out the object, you’ll see an  
“errors” attribute filled with the appropriate errors.

Jason

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**Author:** ![gamehack](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/a3d4f5/32.png) [@gamehack](https://www.ruby-forum.com/u/gamehack)\
**Post date:** [December 25, 2007, 12:58am UTC](https://www.ruby-forum.com/t/forms-and-activerecord-validation-magic/124117/3 "2007-12-25T00:58:17Z")

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Thank you. I realized that the only difference is that the next time  
the method is called, a all to #save would have been made, which would  
have triggered the validations which might in turn make  
obj.errors.count != 0. So the form functions actually check whether  
the number of errors is 0 or not. Thanks for the tip.

g