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POSetting virtual model attribute from controller create action in Rails 4 - attribute always nil
 

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  1. POSetting virtual model attribute from controller create action in Rails 4 - attribute always nil
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    <p>Some background: I have a Rails 4 model with a decimal column <code>d</code>. When being saved or viewed in the app, the value may need to be converted to or from an integer value, respectively, based on the current user's preference.</p> <p>It seems most appropriate that the calculations should go in the model, and should have no knowledge of users.</p> <p>After doing some searching, it seems to me the best way to achieve this is via 2 virtual attributes on the model: one for the current user's preferred format and one for the value, with any calculation applied.</p> <p>So I have come up with something like this:</p> <pre><code>attr_accessor :format, :value_converted def value_converted if format.nil? format = 'A' end if format == 'A' Converter.new(d).to_i if d else d if d end end def value_converted=(value) if format.nil? format = 'A' end if format == 'A' self.d = Converter.new(value.to_i).to_f else self.d = value end </code></pre> <p>Forms refer to the <code>value_converted</code> rather than the <code>d</code>, and this works fine for editing, updating and viewing. The problem is the <code>#create</code> action.</p> <p>I believe the issue is happening because the setter is accessing <code>format</code>, and I can't seem to figure out a way to set <code>format</code> from <code>#create</code> before the setter is called, in other words when <code>new</code> creates the object.</p> <p>I thought perhaps I could just pass the <code>format</code> along with the other parameters (as in <a href="https://stackoverflow.com/questions/16530532/rails-4-insert-attribute-into-params">this answer</a>, so I tried merging it in, both within and after the standard strong parameters fare, but with no luck:</p> <p>Both</p> <pre><code>@entry = current_user.entries.new(entry_params.merge(format: current_user.format)) </code></pre> <p>and</p> <pre><code>params.require(:entry).permit(:value_converted, :other_param, ...).merge(format: current_user.format) </code></pre> <p>do not raise any errors, but are apparently ignored. However simply passing <code>format</code> to <code>new</code> in the console works fine.</p> <p>So my question: Does anyone have a solution to this problem? Or perhaps a better/more appropriate way of going about it? It seems like it should be something simple.</p> <p>Thanks for any help</p>
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