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    <p>There are several issues with each of the available methods, but I believe that defining an <code>after_initialize</code> callback is the way to go for the following reasons:</p> <ol> <li><code>default_scope</code> will initialize values for new models, but then that will become the scope on which you find the model. If you just want to initialize some numbers to 0 then this is <em>not</em> what you want.</li> <li>Defining defaults in your migration also works part of the time... As has already been mentioned this will <em>not</em> work when you just call Model.new.</li> <li>Overriding <code>initialize</code> can work, but don't forget to call <code>super</code>!</li> <li>Using a plugin like phusion's is getting a bit ridiculous. This is ruby, do we really need a plugin just to initialize some default values?</li> <li>Overriding <code>after_initialize</code> <strong>is deprecated</strong> as of Rails 3. When I override <code>after_initialize</code> in rails 3.0.3 I get the following warning in the console:</li> </ol> <blockquote> <p>DEPRECATION WARNING: Base#after_initialize has been deprecated, please use Base.after_initialize :method instead. (called from /Users/me/myapp/app/models/my_model:15)</p> </blockquote> <p>Therefore I'd say write an <code>after_initialize</code> callback, which lets you default attributes <em>in addition to</em> letting you set defaults on associations like so:</p> <pre><code> class Person &lt; ActiveRecord::Base has_one :address after_initialize :init def init self.number ||= 0.0 #will set the default value only if it's nil self.address ||= build_address #let's you set a default association end end </code></pre> <p>Now you have <strong>just one</strong> place to look for initialization of your models. I'm using this method until someone comes up with a better one.</p> <p>Caveats:</p> <ol> <li><p>For boolean fields do:</p> <p><code>self.bool_field = true if self.bool_field.nil?</code></p> <p>See Paul Russell's comment on this answer for more details</p></li> <li><p>If you're only selecting a subset of columns for a model (ie; using <code>select</code> in a query like <code>Person.select(:firstname, :lastname).all</code>) you will get a <code>MissingAttributeError</code> if your <code>init</code> method accesses a column that hasn't been included in the <code>select</code> clause. You can guard against this case like so:</p> <p><code>self.number ||= 0.0 if self.has_attribute? :number</code></p> <p>and for a boolean column...</p> <p><code>self.bool_field = true if (self.has_attribute? :bool_value) &amp;&amp; self.bool_field.nil?</code></p> <p>Also note that the syntax is different prior to Rails 3.2 (see Cliff Darling's comment below)</p></li> </ol>
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    1. POHow can I set default values in ActiveRecord?
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    1. USJeff Perrin
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    1. POHow can I set default values in ActiveRecord?
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    1. COThis definitely appears to be the best way to achieve this. Which is really odd and unfortunate. A sensible preferred method for establishing model attribute defaults upon creation seems like something Rails should already have built in. The only other (reliable) way, overriding `initialize`, just seems really convoluted for something that should be clear and well defined. I spent hours crawling through the documentation before searching here because I assumed this functionality was already there somewhere and I just wasn't aware of it.
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      1. USseaneshbaugh
    2. COOne note on this - if you have a boolean field that you want to default, don't do `self.bool_field ||= true`, as this'll force the field to true even if you explicitly initialise it to false. Instead do `self.bool_field = true if self.bool_field.nil?`.
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      1. USPaul Russell
    3. CORegarding point #2, Model.new actually works (only for me ?) together with defaults defined in migrations, or more exactly with default values for table columns. But I recognize that Jeff's method based on the after_initialize callback is probably the best way to do. Just a question: does it work with dirty yet unsaved objects ? In your example, will Person.new.number_was return 0.0 ?
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      1. USLaurent Farcy
 

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