# Database and migration question

**URL:** <https://www.ruby-forum.com/t/database-and-migration-question/91105>\
**Category:** Rails\
**Created:** [April 4, 2007, 7:32pm UTC](https://www.ruby-forum.com/t/database-and-migration-question/91105 "2007-04-04T19:32:47Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![nuby2ruby](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/54ee81/32.png) [@nuby2ruby](https://www.ruby-forum.com/u/nuby2ruby)\
**Post date:** [April 4, 2007, 7:32pm UTC](https://www.ruby-forum.com/t/database-and-migration-question/91105/1 "2007-04-04T19:32:47Z")

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I have a problem with a project I am working on.

What I would like to know is, is there a way to create a field in a  
database dynamically after an action from a user is done. Such that the  
user can create a field on the fly and create as many as they want?

The story.

I have an ecom site and we sell products, but the price components (i.e.  
tax, cost, markup ect.) are dynamic. The way the company wants it set  
up, there are identifiers. The user can make as many identifiers as they  
want. An identifier would be tax, cost, markup, or maybe something like  
fee. The goal is that I don’t care how many they make, but we need to  
save these to the DB. We can make a static number of fields, but if they  
make more identifiers then we have to go back manually and run a new  
migration. I want to get away from this if at all possible.

If anyone has a better idea, i’m totally down with it. Any help would be  
great.

Thanks,

Jeremy

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<div class="post-metadata">

**Author:** ![nuby2ruby](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/54ee81/32.png) [@nuby2ruby](https://www.ruby-forum.com/u/nuby2ruby)\
**Post date:** [April 4, 2007, 8:31pm UTC](https://www.ruby-forum.com/t/database-and-migration-question/91105/2 "2007-04-04T20:31:33Z")

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Jeremy W. wrote:

> I have a problem with a project I am working on.
> 
> What I would like to know is, is there a way to create a field in a  
> database dynamically after an action from a user is done. Such that the  
> user can create a field on the fly and create as many as they want?
> 
> The story.
> 
> I have an ecom site and we sell products, but the price components (i.e.  
> tax, cost, markup ect.) are dynamic. The way the company wants it set  
> up, there are identifiers. The user can make as many identifiers as they  
> want. An identifier would be tax, cost, markup, or maybe something like  
> fee. The goal is that I don’t care how many they make, but we need to  
> save these to the DB. We can make a static number of fields, but if they  
> make more identifiers then we have to go back manually and run a new  
> migration. I want to get away from this if at all possible.
> 
> If anyone has a better idea, i’m totally down with it. Any help would be  
> great.
> 
> Thanks,
> 
> Jeremy

This is a classic one-to-many database problem. The solution is to make  
a new table (call it something like price\_components) and connect it to  
your Client table with a foreign key. (I think this is what you want.  
I’m not sure from your description whether each client has their own set  
of price components or each product does.) Assuming your clients are in  
a `clients` table it might look something like:

create\_table ‘price\_components’ do |t|  
t.column ‘client\_id’, :integer, :null=\>false  
t.column ‘name’, :string # tax,cost, markup, etc…  
t.column ‘amount’, :float  
end

Then a model for it: app/model/price\_component.rb

class PriceComponent \< ActiveRecord::Base  
belongs\_to :client  
end

And in your original model: app/model/client.rb

class client \< ActiveRecord::Base  
has\_many :price\_components

#rest of the model goes here

end