# Find when you have the model name but not the class **URL:** \ **Category:** Rails\ **Created:** [November 10, 2006, 5:54pm UTC](https://www.ruby-forum.com/t/find-when-you-have-the-model-name-but-not-the-class/75521 "2006-11-10T17:54:28Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![reggieb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/3e96dc/32.png) [@reggieb](https://www.ruby-forum.com/u/reggieb)\ **Post date:** [November 10, 2006, 5:54pm UTC](https://www.ruby-forum.com/t/find-when-you-have-the-model-name-but-not-the-class/75521/1 "2006-11-10T17:54:28Z")
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: ```auto 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 ``` I am then able to list the history of a particular item, or all history. In the list of all history, I use: ```auto <% if Stock.find(:first, :conditions => ["id = ?", history.item_id.to_i]) -%> <%= link_to "#{history.model}/#{history.item_id}", :controller => history.model.pluralize.downcase, :action => "show", :id => history.item_id -%> <% else -%> <%=h history.model -%>/<%=h history.item_id -%> <% end -%> ``` 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. ---
**Author:** ![reggieb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/3e96dc/32.png) [@reggieb](https://www.ruby-forum.com/u/reggieb)\ **Post date:** [November 10, 2006, 6:19pm UTC](https://www.ruby-forum.com/t/find-when-you-have-the-model-name-but-not-the-class/75521/2 "2006-11-10T18:19:54Z")
Try: eval(model\_name).find(:all) ---
**Author:** ![reggieb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/3e96dc/32.png) [@reggieb](https://www.ruby-forum.com/u/reggieb)\ **Post date:** [November 10, 2006, 6:01pm UTC](https://www.ruby-forum.com/t/find-when-you-have-the-model-name-but-not-the-class/75521/3 "2006-11-10T18:01:53Z")
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 ---
**Author:** ![reggieb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/3e96dc/32.png) [@reggieb](https://www.ruby-forum.com/u/reggieb)\ **Post date:** [November 10, 2006, 6:24pm UTC](https://www.ruby-forum.com/t/find-when-you-have-the-model-name-but-not-the-class/75521/4 "2006-11-10T18:24:56Z")
2 ways I know of… Object.const\_get(“MyClass”) eval(“MyClass”) not sure which is more efficient ---
**Author:** ![reggieb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/3e96dc/32.png) [@reggieb](https://www.ruby-forum.com/u/reggieb)\ **Post date:** [November 10, 2006, 6:51pm UTC](https://www.ruby-forum.com/t/find-when-you-have-the-model-name-but-not-the-class/75521/5 "2006-11-10T18:51:08Z")
David F. 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. ---
**Author:** ![reggieb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/3e96dc/32.png) [@reggieb](https://www.ruby-forum.com/u/reggieb)\ **Post date:** [November 10, 2006, 6:59pm UTC](https://www.ruby-forum.com/t/find-when-you-have-the-model-name-but-not-the-class/75521/6 "2006-11-10T18:59:18Z")
Frederick C. 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 ---
**Author:** ![reggieb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/3e96dc/32.png) [@reggieb](https://www.ruby-forum.com/u/reggieb)\ **Post date:** [November 10, 2006, 7:00pm UTC](https://www.ruby-forum.com/t/find-when-you-have-the-model-name-but-not-the-class/75521/7 "2006-11-10T19:00:26Z")
Rob N. wrote: > > always HistoryItem I think. In fact ItemHistory ---
**Author:** ![reggieb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/3e96dc/32.png) [@reggieb](https://www.ruby-forum.com/u/reggieb)\ **Post date:** [November 10, 2006, 7:11pm UTC](https://www.ruby-forum.com/t/find-when-you-have-the-model-name-but-not-the-class/75521/8 "2006-11-10T19:11:05Z")
Rob N. wrote: > 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 P. removed\_email\_address@domain.invalid