# How does rails handle wrong/malformed datatypes

**URL:** <https://www.ruby-forum.com/t/how-does-rails-handle-wrong-malformed-datatypes/87322>\
**Category:** Rails\
**Created:** [March 1, 2007, 7:32pm UTC](https://www.ruby-forum.com/t/how-does-rails-handle-wrong-malformed-datatypes/87322 "2007-03-01T19:32:34Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![austin7873](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/f19dbf/32.png) [@austin7873](https://www.ruby-forum.com/u/austin7873)\
**Post date:** [March 1, 2007, 7:32pm UTC](https://www.ruby-forum.com/t/how-does-rails-handle-wrong-malformed-datatypes/87322/1 "2007-03-01T19:32:34Z")

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Hi,

I need help understanding how rails handles setting object attributes  
with the wrong datatype. Specifically a datetime attribute, but the  
behavior happens with other data types too (I’ve also tried with  
integers)

I’m thinking that rails does some magic behind the scenes and if it  
senses that you’re trying  
to set an attribute with the wrong data type, for example, datetime with  
“asdf”, it returns nil, or integer with “asdf”, it returns 0.

Validating then becomes a bit more difficult!

In a real example, I have a people table in my database with a birthdate  
attribute:

create\_table “people”, :force =\> true do |t|  
t.column “name”, :string  
t.column “age”, :integer  
t.column “birthdate”, :datetime  
end

On my form I try to submit a date with the value “abcdef”, which is not  
a valid date format.  
My people\_controller.rb then creates a new instance of person and, for  
now, simply prints the brithdate.

def create  
@person = Person.new(params[:person])  
puts @person.birthdate  
end

or with “ruby script/console”

> > person = Person.new(:name=\>“foo”, :age =\> “bar”, :birthdate =\> “baz”)  
> > =\> #\<Person:0x327d80c @attributes={“name”=\>“foo”, “age”=\>“bar”  
> > “birthdate”=\>“baz”}, @new\_record=true\>
> 
> > puts person.birthdate  
> > nil  
> > =\> nil

In either script/console, or the controller, if I print the whole object  
with:

> > puts person.to\_xml

birthdate is also nil. however if I print with:

> > puts person.to\_yaml

I do see the malformed value in the object. So from there, if I try to  
do any validation in the person model, person.rb, during a save.

> > person.save

or in the controller

def create  
@person = Person.new(params[:person])  
@person.save  
end

I’m still not able to see the value in person.birthdate:

def validate  
puts self.birthdate # returns nil  
puts attributes[‘birthdate’] # returns nil  
puts self.to\_xml # returns a nil value for birthdate in the  
output  
puts self.to\_yaml # returns the error “wrong argument type nil  
(expected Data)”  
end

How can I validate the date is in the correct format if the object  
returns nil for the value?

---

<div class="post-metadata">

**Author:** ![austin7873](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/f19dbf/32.png) [@austin7873](https://www.ruby-forum.com/u/austin7873)\
**Post date:** [March 1, 2007, 8:24pm UTC](https://www.ruby-forum.com/t/how-does-rails-handle-wrong-malformed-datatypes/87322/2 "2007-03-01T20:24:05Z")

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Heh. Found it last night: before\_type\_cast. So take a look at the value  
of birthdate\_before\_type\_cast in your controller. 🙂

b