Activemodel::Missingattributeerror Occurs After Deploying and Then Goes Away After a While

In a Rails ActiveRecord model, is using after_initialize callbacks a very bad idea?

Most uses of after_initialize can be (and SHOULD be) replaced with defaults on the corresponding database columns. If you're setting the property to a constant value, you may want to look into this as an alternative.

EDIT: if the value isn't constant, a call to has_attribute?(:name) will guard against this error - ActiveModel::MissingAttributeError occurs after deploying and then goes away after a while

ActiveModel::MissingAttributeError (can't write unknown attribute `user_id`)

You'll need to add a user_id column to your comments table. The belongs_to requires this. You're also going to need a post_id column, and user_id for your posts table to.

You can customise the column name, but the convention is to use the format parent_table_id.

Here's the key quote, from the docs:

Associations are implemented using macro-style calls, so that you can
declaratively add features to your models. For example, by declaring
that one model belongs_to another, you instruct Rails to maintain
Primary Key-Foreign Key information between instances of the two
models, and you also get a number of utility methods added to your
model.

This means, for example, if your first user has an id of 1, all of their comments and posts will have a user_id value of 1, which does the actual tying together of the records.

Here's an example migration with the relevant line included:

def change 
  create_table :comments do |t|
    ...
    t.belongs_to :user, index: true
    ...
  end
end

Does that make sense? Let me know if you've any questions and I can update as needed :)

ActiveModel dymamic methods in instance objects

you can add methods with singleton_class.module_eval

def initialize(attributes = {})
   set_default_attributes!
   @attributes.each do |key,value|
     singleton_class.module_eval do
       define_method(key) { self.attributes[key] } unless method_defined? key
       define_method("#{key}=") { |new_value|  self.attributes[key] = new_value } unless method_defined? "#{key}="
     end
   end
   @attributes.merge!(attributes.symbolize_keys)
   @new_record = true

 end

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