# Rake db:migrate as in Agile Web Development with Rails

**URL:** <https://www.ruby-forum.com/t/rake-db-migrate-as-in-agile-web-development-with-rails/83789>\
**Category:** Rails\
**Created:** [January 29, 2007, 7:07pm UTC](https://www.ruby-forum.com/t/rake-db-migrate-as-in-agile-web-development-with-rails/83789 "2007-01-29T19:07:57Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![XBone](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/x/e480ec/32.png) [@XBone](https://www.ruby-forum.com/u/XBone)\
**Post date:** [January 29, 2007, 7:07pm UTC](https://www.ruby-forum.com/t/rake-db-migrate-as-in-agile-web-development-with-rails/83789/1 "2007-01-29T19:07:57Z")

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Reading Agile Web D. with Rails (2nd edition)  
Working with InstantRails on Windows XP Professional Sevice Pack 2

I am trying to run a migration using the command  
rake db:migrate  
from the command prompt.

This is the error I’m getting:

rake aborted!  
You have a nil object when you didn’t expect it!  
You might have expected an instance of Array.  
The error occured while evaluating nil.[]

Any ideas why is this occurring and how I can solve this?

Thanks

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**Author:** ![XBone](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/x/e480ec/32.png) [@XBone](https://www.ruby-forum.com/u/XBone)\
**Post date:** [January 29, 2007, 7:11pm UTC](https://www.ruby-forum.com/t/rake-db-migrate-as-in-agile-web-development-with-rails/83789/2 "2007-01-29T19:11:59Z")

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On 1/29/07, XBone [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> rake aborted!  
> You have a nil object when you didn’t expect it!  
> You might have expected an instance of Array.  
> The error occured while evaluating nil.[]

I had a similar error. In my case, the problem was that I was trying to  
alter an existing table by adding a foreign key reference to a table  
that  
had existing data in it. I had a previous migration that added some test  
data for me. Specifically, for me, the problem was that I was trying to  
explicitly add the constraint in MySQL. I removed the constraint and let  
rails handle the relationship (probably not the best idea, but I am  
still  
learning and playing) and the error went away.

## Chris

[www.fuzzylizard.com](http://www.fuzzylizard.com)

You know you’ve achieved perfection in design, Not when you have nothing  
more to add, But when you have nothing more to take away.  
— Antoine de Saint-Exupery

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**Author:** ![XBone](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/x/e480ec/32.png) [@XBone](https://www.ruby-forum.com/u/XBone)\
**Post date:** [January 29, 2007, 7:47pm UTC](https://www.ruby-forum.com/t/rake-db-migrate-as-in-agile-web-development-with-rails/83789/3 "2007-01-29T19:47:21Z")

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Hi. Thanks for your reply.

However, I have not added constraints through other database interfaces.

My migration is named 002\_add\_price.rb and this is its contents:

class AddPrice \< ActiveRecord::Migration  
def self.up  
add\_column :products, :price, :decimal, :precision =\> 8, :scale =\>  
2, :default =\> 0  
end

def self.down  
remove\_column :products, :price  
end  
end

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<div class="post-metadata">

**Author:** ![XBone](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/x/e480ec/32.png) [@XBone](https://www.ruby-forum.com/u/XBone)\
**Post date:** [January 29, 2007, 7:55pm UTC](https://www.ruby-forum.com/t/rake-db-migrate-as-in-agile-web-development-with-rails/83789/4 "2007-01-29T19:55:03Z")

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Guest wrote:

> Hi. Thanks for your reply.

I had the same issue and it was related to not running Rails 1.2. All  
examples in the book assume you’re using this version of Rails, not sure  
if this will be helpful in your case.

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**Author:** ![XBone](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/x/e480ec/32.png) [@XBone](https://www.ruby-forum.com/u/XBone)\
**Post date:** [January 29, 2007, 8:04pm UTC](https://www.ruby-forum.com/t/rake-db-migrate-as-in-agile-web-development-with-rails/83789/5 "2007-01-29T20:04:16Z")

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There was the exact same thread on here a few days ago…

Upgrading to 1.2 should fix your problems.

Best,  
Jamie

On Jan 29, 10:55 am, Drew O. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)

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**Author:** ![XBone](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/x/e480ec/32.png) [@XBone](https://www.ruby-forum.com/u/XBone)\
**Post date:** [January 30, 2007, 6:12pm UTC](https://www.ruby-forum.com/t/rake-db-migrate-as-in-agile-web-development-with-rails/83789/6 "2007-01-30T18:12:20Z")

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Yup, I just ran into this yesterday and it was because I was not  
running 1.2.1. Upgrade and you are good to go.

Scott