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Rob Nichols

2006-Nov-10 16:54 UTC

Find when you have the model name but not the class

Hi,

How can I get a model class and then search on it if I only have the 
model name?

I have created an item_history to track the changes of an item in a 
stock list. I use this method in the Stock model, to create the history 
information:
[code]
def add_history(item, process)
    history = ItemHistory.new
    history.model = item.class.to_s
    history.item_id = item.id
    history.status = item.stock_status.name
    history.comments = item.comments
    history.process_name = process
    if user = User.find(session[:user_id])
      history.who = user.user_name
    end
    history.save
  end
[/code]

I am then able to list the history of a particular item, or all history. 
In the list of all history, I use:
[code]
<% if Stock.find(:first, :conditions => ["id = ?", 
history.item_id.to_i]) -%>
            <td><%= link_to
"#{history.model}/#{history.item_id}",
                    :controller => history.model.pluralize.downcase,
                    :action => "show",
                    :id => history.item_id -%></td>
          <% else -%>
            <td><%=h history.model -%>/<%=h history.item_id
-%></td>
          <% end -%>
[/code]
This either outputs model/id or the same with a link to that item if the 
item exists (if the action being recorded is delete, the item won''t be 
there).

How do I recreate the "if Stock.find" statement to accept any model 
name. I want something the will let me grab an instance of the model 
class by passing history.model to it, and then let me do a find on that 
class.

Is that possible?

I want to reuse this system in another model.

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Frederick Cheung

2006-Nov-10 17:01 UTC

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Re: Find when you have the model name but not the class

You can do history.item.class.find ...
Which will do a Stock.find if item is an instance of class Stock, 
Badger.find if item is an instance of Badger etc...

Fred

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David Fitzgibbon

2006-Nov-10 17:19 UTC

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Re: Find when you have the model name but not the class

Try:

eval(model_name).find(:all)

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Chris Hall

2006-Nov-10 17:22 UTC

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Re: Find when you have the model name but not the class

2 ways I know of...

Object.const_get("MyClass")

eval("MyClass")

not sure which is more efficient

On 11/10/06, Rob Nichols
<rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:>
> Hi,
>
> How can I get a model class and then search on it if I only have the
> model name?
>
> I have created an item_history to track the changes of an item in a
> stock list. I use this method in the Stock model, to create the history
> information:
> [code]
> def add_history(item, process)
>     history = ItemHistory.new
>     history.model = item.class.to_s
>     history.item_id = item.id
>     history.status = item.stock_status.name
>     history.comments = item.comments
>     history.process_name = process
>     if user = User.find(session[:user_id])
>       history.who = user.user_name
>     end
>     history.save
>   end
> [/code]
>
> I am then able to list the history of a particular item, or all history.
> In the list of all history, I use:
> [code]
> <% if Stock.find(:first, :conditions => ["id = ?",
> history.item_id.to_i]) -%>
>             <td><%= link_to
"#{history.model}/#{history.item_id}",
>                     :controller => history.model.pluralize.downcase,
>                     :action => "show",
>                     :id => history.item_id -%></td>
>           <% else -%>
>             <td><%=h history.model -%>/<%=h history.item_id
-%></td>
>           <% end -%>
> [/code]
> This either outputs model/id or the same with a link to that item if the
> item exists (if the action being recorded is delete, the item
won''t be
> there).
>
> How do I recreate the "if Stock.find" statement to accept any
model
> name. I want something the will let me grab an instance of the model
> class by passing history.model to it, and then let me do a find on that
> class.
>
> Is that possible?
>
> I want to reuse this system in another model.
>
> --
> Posted via http://www.ruby-forum.com/.
>
> >
>
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Rob Nichols

2006-Nov-10 17:51 UTC

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Re: Find when you have the model name but not the class

David Fitzgibbon wrote:> Try:
> 
> eval(model_name).find(:all)
Splendid. This worked a treat:

if eval(history.model).find(:first, :conditions => ["id = ?", 
history.item_id.to_i])

Thank you David and Chris for your prompt and useful responses.


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Rob Nichols

2006-Nov-10 17:59 UTC

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Re: Find when you have the model name but not the class

Frederick Cheung wrote:> You can do history.item.class.find ...
> Which will do a Stock.find if item is an instance of class Stock, 
> Badger.find if item is an instance of Badger etc...
> 
> Fred
Thanks Fred. I missed that when I responded earlier.

I don''t think that will work because I am only storing the model name
in
history_item, and not an instance of the model class. The class of the 
history object is always HistoryItem I think.

Rob

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Rob Nichols

2006-Nov-10 18:00 UTC

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Re: Find when you have the model name but not the class

Rob Nichols wrote:
>> always HistoryItem I think.
In fact ItemHistory


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Gustav Paul

2006-Nov-10 18:05 UTC

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Re: Find when you have the model name but not the class

Rob Nichols wrote:> David Fitzgibbon wrote:
>   
>> Try:
>>
>> eval(model_name).find(:all)
>>     
>
> Splendid. This worked a treat:
>
> if eval(history.model).find(:first, :conditions => ["id = ?", 
> history.item_id.to_i])
>
> Thank you David and Chris for your prompt and useful responses.
>
>
>   You can also do model_name.constantize.find......
if however ''model_name'' isn''t the actual name of the
class - meaning
''MyTable'' and not eg. ''my_tables'' - you need
to call classify first, eg.
model_name.classify.constantize.find...

eval is also pretty cool though :]

Hope this helps!
Cheery-o
Gustav Paul
gustav-PUm+PnBUKx7YkQIYctQFYw@public.gmane.org

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Rails - Nov 2006 - Find when you have the model name but not the class

Find when you have the model name but not the class

Re: Find when you have the model name but not the class

Re: Find when you have the model name but not the class

Re: Find when you have the model name but not the class

Re: Find when you have the model name but not the class

Re: Find when you have the model name but not the class

Re: Find when you have the model name but not the class

Re: Find when you have the model name but not the class