How to set default values in Rails

Question

I m trying to find the best way to set default values for objects in Rails     The best I can think of is to set the default value in the new method in the controller    Does anyone have any input if this is acceptable or if there s a better way to do it

User · Answer

If you re talking about ActiveRecord objects  I use the  attribute-defaults  gem   Documentation  amp  download  https   github com bsm attribute-defaults

User · Answer

The suggestion to override new initialize is probably incomplete   Rails will  frequently  call allocate for ActiveRecord objects  and calls to allocate won t result in calls to initialize   If you re talking about ActiveRecord objects  take a look at overriding after initialize   These blog posts  not mine  are useful   Default values Default constructors not called   Edit  SFEley points out that Rails actually does look at the default in the database when it instantiates a new object in memory - I hadn t realized that

User · Answer

Correct  is a dangerous word in Ruby   There s usually more than one way to do anything   If you know you ll always want that default value for that column on that table  setting them in a DB migration file is the easiest way   class SetDefault  lt  ActiveRecord  Migration   def self up     change column  people   last name   type   default   gt   Doe    end    def self down       You can t currently remove default values in Rails     raise ActiveRecord  IrreversibleMigration   Can t remove the default    end end   Because ActiveRecord autodiscovers your table and column properties  this will cause the same default to be set in any model using it in any standard Rails app   However  if you only want default values set in specific cases -- say  it s an inherited model that shares a table with some others -- then another elegant way is do it directly in your Rails code when the model object is created   class GenericPerson  lt  Person   def initialize attributes nil      attr with defaults     last name   gt   Doe   merge attributes      super attr with defaults    end end   Then  when you do a GenericPerson new    it ll always trickle the  Doe  attribute up to Person new   unless you override it with something else

User · Answer

A potentially even better cleaner potential way than the answers proposed is to overwrite the accessor  like this   def status   self  name of var       desired default value  end   See  Overwriting default accessors  in the ActiveRecord  Base documentation and more from StackOverflow on using self

User · Answer

If you are referring to ActiveRecord objects  you have  more than  two ways of doing this   1  Use a  default parameter in the DB  E G   class AddSsl  lt  ActiveRecord  Migration   def self up     add column  accounts   ssl enabled   boolean   default   gt  true   end    def self down     remove column  accounts   ssl enabled   end end   More info here  http   api rubyonrails org classes ActiveRecord Migration html  2  Use a callback  E G  before validation on create  More info here  http   api rubyonrails org classes ActiveRecord Callbacks html M002147

User · Answer

i answered a similar question here   a clean way to do this is using Rails attr accessor with default  class SOF   attr accessor with default  is awesome true end  sof   SOF new sof is awesome    gt  true   UPDATE  attr accessor with default has been deprecated in Rails 3 2   you could do this instead with pure Ruby  class SOF   attr writer  is awesome    def is awesome      is awesome     true   end end  sof   SOF new sof is awesome     gt  true

User · Answer

You can also try change column default in your migrations  tested in Rails 3 2 8    class SetDefault  lt  ActiveRecord  Migration   def up       Set default value     change column default  people   last name   Smith    end    def down       Remove default     change column default  people   last name  nil   end end   change column default Rails API docs

User · Answer

First of all you can t overload initialize  args  as it s not called in all cases   Your best option is to put your defaults into your migration   add column  accounts   max users   integer   default   gt  10   Second best is to place defaults into your model but this will only work with attributes that are initially nil  You may have trouble as I did with boolean columns   def after initialize   if new record      max users     10   end end   You need the new record  so the defaults don t override values loaded from the datbase    You need     to stop Rails from overriding parameters passed into the initialize method

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I needed to set a default just as if it was specified as default column value in DB  So it behaves like this  a   Item new a published at     gt  my default value  a   Item new  published at   gt  nil  a published at     gt  nil   Because after initialize callback is called after setting attributes from arguments  there was no way to know if the attribute is nil because it was never set or because it was intentionally set as nil  So I had to poke inside a bit and came with this simple solution   class Item  lt  ActiveRecord  Base   def self column defaults     super merge  published at    gt  Time now    end end   Works great for me   Rails 3 2 x

User · Answer

You can override the constructor for the ActiveRecord model   Like this   def initialize  args    super  args    self attribute that needs default value     default value   self attribute that needs another default value     another default value    ad nauseum end

User · Answer

Generate a migration and use change column default  is succinct and reversible   class SetDefaultAgeInPeople  lt  ActiveRecord  Migration 5 2    def change     change column default  people   age    from  nil  to  0     end end

User · Answer

If you are just setting defaults for certain attributes of a database backed model I d consider using sql default column values - can you clarify what types of defaults you are using   There are a number of approaches to handle it  this plugin looks like an interesting option

User · Answer

For boolean fields in Rails 3 2 6 at least  this will work in your migration   def change   add column  users   eula accepted   boolean  default  false end   Putting a 1 or 0 for a default will not work here  since it is a boolean field  It must be a true or false value

User · Answer

Based on SFEley s answer  here is an updated fixed one for newer Rails versions   class SetDefault  lt  ActiveRecord  Migration   def change     change column  table name   column name   type  default   Your value    end end

User · Answer

You could use the rails default value gem  eg   class Foo  lt  ActiveRecord  Base           default  bar   gt   some default value          end   https   github com keithrowell rails default value

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In case you re dealing with a Model  you can use the Attriutes API in Rails 5  http   api rubyonrails org classes ActiveRecord Attributes ClassMethods html method-i-attribute  just add a migration with a proper column name and then in the model set it with   class StoreListing  lt  ActiveRecord  Base   attribute  country   string  default   PT  end

User · Answer

In Ruby on Rails v3 2 8  using the after initialize ActiveRecord callback  you can call a method in your model that will assign the default values for a new object      after initialize callback is triggered for each object that is found and instantiated by a finder  with after initialize being triggered after new objects are instantiated as well    see ActiveRecord Callbacks     So  IMO it should look something like   class Foo  lt  ActiveRecord  Base   after initialize  assign defaults on new Foo         attr accessible  bar         private   def assign defaults on new Foo       required to check an attribute for existence to weed out existing records     self bar   default value unless self attribute whose presence has been validated   end end   Foo bar   default value for this instance unless the instance contains an attribute whose presence has been validated previously on save update  The default value will then be used in conjunction with your view to render the form using the default value for the bar attribute   At best this is hacky     EDIT - use  new record   to check if instantiating from a new call  Instead of checking an attribute value  use the new record  built-in method with rails  So  the above example should look like   class Foo  lt  ActiveRecord  Base   after initialize  assign defaults on new Foo  if   new record           attr accessible  bar         private   def assign defaults on new Foo     self bar   default value   end end   This is much cleaner  Ah  the magic of Rails - it s smarter than me

[ruby-on-rails] How to set default values in Rails?

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