Rails How can I set default values in ActiveRecord

Question

How can I set default value in ActiveRecord   I see a post from Pratik that describes an ugly  complicated chunk of code  http   m onkey org 2007 7 24 how-to-set-default-values-in-your-model  class Item  lt  ActiveRecord  Base     def initialize with defaults attrs   nil   amp block      initialize without defaults attrs  do       setter   lambda    key  value  self send    key to s     value  unless          attrs nil   amp  amp  attrs keys map  amp  to s  include  key to s          setter call  scheduler type    hotseat         yield self if block given      end   end   alias method chain  initialize   defaults end   I have seen the following examples googling around     def initialize      super     self status   ACTIVE unless self status   end   and    def after initialize      return unless new record      self status   ACTIVE   end   I ve also seen people put it in their migration  but I d rather see it defined in the model code   Is there a canonical way to set default value for fields in ActiveRecord model

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The Phusion guys have some nice plugin for this

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https   github com keithrowell rails default value  class Task  lt  ActiveRecord  Base   default  status   gt   active  end

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This is what constructors are for  Override the model s initialize method   Use the after initialize method

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I strongly suggest using the  default value for  gem  https   github com FooBarWidget default value for  There are some tricky scenarios that pretty much require overriding the initialize method  which that gem does   Examples   Your db default is NULL  your model ruby-defined default is  some string   but you actually want to set the value to nil for whatever reason  MyModel new my attr  nil   Most solutions here will fail to set the value to nil  and will instead set it to the default   OK  so instead of taking the     approach  you switch to my attr changed      BUT now imagine your db default is  some string   your model ruby-defined default is  some other string   but under a certain scenario  you want to set the value to  some string   the db default   MyModel new my attr   some string    This will result in my attr changed  being false because the value matches the db default  which in turn will fire your ruby-defined default code and set the value to  some other string  -- again  not what you desired     For those reasons I don t think this can properly be accomplished with just an after initialize hook   Again  I think the  default value for  gem is taking the right approach  https   github com FooBarWidget default value for

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The problem with the after initialize solutions is that you have to add an after initialize to every single object you look up out of the DB  regardless of whether you access this attribute or not  I suggest a lazy-loaded approach    The attribute methods  getters  are of course methods themselves  so you can override them and provide a default  Something like   Class Foo  lt  ActiveRecord  Base     has a DB column field atttribute called  status    def status      val   read attribute  status   nil     ACTIVE    val   end end   Unless  like someone pointed out  you need to do Foo find by status  ACTIVE    In that case I think you d really need to set the default in your database constraints  if the DB supports it

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This has been answered for a long time  but I need default values frequently and prefer not to put them in the database  I create a DefaultValues concern   module DefaultValues   extend ActiveSupport  Concern    class methods do     def defaults attr  to  nil  on   initialize        method name    set default   attr         send  after   on    method name to sym        define method method name  do         if send attr            send attr          else           value   to is a  Proc    to call   to           send    attr     value          end       end        private method name     end   end end   And then use it in my models like so   class Widget  lt  ApplicationRecord   include DefaultValues    defaults  category  to   uncategorized    defaults  token  to  - gt    SecureRandom uuid   end

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class Item  lt  ActiveRecord  Base   def status     self  status  or ACTIVE   end    before save  self status     ACTIVE   end

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If the column happens to be a  status  type column  and your model lends itself to the use of state machines  consider using the aasm gem  after which you can simply do     aasm column   status  do     state  available  initial  true     state  used       transitions   end   It still doesn t initialize the value for unsaved records  but it s a bit cleaner than rolling your own with init or whatever  and you reap the other benefits of aasm such as scopes for all your statuses

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I use the attribute-defaults gem  From the documentation  run sudo gem install attribute-defaults and add require  attribute defaults  to your app   class Foo  lt  ActiveRecord  Base   attr default  age  18   attr default  last seen do     Time now   end end  Foo new                 gt  age  18  last seen   gt   2014-10-17 09 44 27  Foo new  age   gt  25      gt  age  25  last seen   gt   2014-10-17 09 44 28

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Sup guys  I ended up doing the following   def after initialize   self extras       self other stuff    This stuff  end   Works like a charm

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There are several issues with each of the available methods  but I believe that defining an after initialize callback is the way to go for the following reasons    default scope 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 not what you want  Defining defaults in your migration also works part of the time    As has already been mentioned this will not work when you just call Model new  Overriding initialize can work  but don t forget to call super  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  Overriding after initialize is deprecated as of Rails 3  When I override after initialize in rails 3 0 3 I get the following warning in the console       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    Therefore I d say write an after initialize callback  which lets you default attributes in addition to letting you set defaults on associations like so     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       Now you have just one place to look for initialization of your models  I m using this method until someone comes up with a better one   Caveats    For boolean fields do   self bool field   true if self bool field nil   See Paul Russell s comment on this answer for more details If you re only selecting a subset of columns for a model  ie  using select in a query like Person select  firstname   lastname  all  you will get a MissingAttributeError if your init method accesses a column that hasn t been included in the select clause  You can guard against this case like so   self number     0 0 if self has attribute   number  and for a boolean column     self bool field   true if  self has attribute   bool value   amp  amp  self bool field nil   Also note that the syntax is different prior to Rails 3 2  see Cliff Darling s comment below

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I ve found that using a validation method provides a lot of control over setting defaults  You can even set defaults  or fail validation  for updates  You even set a different default value for inserts vs updates if you really wanted to  Note that the default won t be set until  valid  is called   class MyModel   validate  init defaults    private   def init defaults     if new record        self some int     1     elsif some int nil        errors add  some int   can t be blank on update       end   end end   Regarding defining an after initialize method  there could be performance issues because after initialize is also called by each object returned by  find   http   guides rubyonrails org active record validations callbacks html after initialize-and-after find

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We put the default values in the database through migrations  by specifying the  default option on each column definition  and let Active Record use these values to set the default for each attribute   IMHO  this approach is aligned with the principles of AR   convention over configuration  DRY  the table definition drives the model  not the other way around   Note that the defaults are still in the application  Ruby  code  though not in the model but in the migration s

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Been using this for a while    post rb class Post  lt  ApplicationRecord   attribute  country   string  default   ID  end

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db schema rb create table  store listings  force  true do  t    t string  my string  default   original default  end  StoreListing new my string     gt   original default     app models store listing rb class StoreListing  lt  ActiveRecord  Base   attribute  my string   string  default   new default  end  StoreListing new my string     gt   new default   class Product  lt  ActiveRecord  Base   attribute  my default proc   datetime  default  - gt    Time now   end  Product new my default proc     gt  2015-05-30 11 04 48 -0600 sleep 1 Product new my default proc     gt  2015-05-30 11 04 49 -0600

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We put the default values in the database through migrations  by specifying the  default option on each column definition  and let Active Record use these values to set the default for each attribute   IMHO  this approach is aligned with the principles of AR   convention over configuration  DRY  the table definition drives the model  not the other way around   Note that the defaults are still in the application  Ruby  code  though not in the model but in the migration s

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From the api docs http   api rubyonrails org classes ActiveRecord Callbacks html Use the before validation method in your model  it gives you the options of creating specific initialisation for create and update calls e g  in this example  again code taken from the api docs example  the number field is initialised for a credit card  You can easily adapt this to set whatever values you want  class CreditCard  lt  ActiveRecord  Base     Strip everything but digits  so the user can specify  555 234 34  or      5552-3434  or both will mean  55523434    before validation  on   gt   create  do     self number   number gsub  r  0-9        if attribute present   number     end end  class Subscription  lt  ActiveRecord  Base   before create  record signup    private     def record signup       self signed up on   Date today     end end  class Firm  lt  ActiveRecord  Base     Destroys the associated clients and people when the firm is destroyed   before destroy    record  Person destroy all  firm id     record id         before destroy    record  Client destroy all  client of     record id     end   Surprised that his has not been suggested here

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Similar questions  but all have slightly different context  - How do I create a default value for attributes in Rails activerecord  39 s model   Best Answer  Depends on What You Want   If you want every object to start with a value  use after initialize  init  You want the new html form to have a default value upon opening the page  use https   stackoverflow com a 5127684 1536309  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    If you want every object to have a value calculated from user input  use before save  default values You want user to enter X and then Y   X  foo   use   class Task  lt  ActiveRecord  Base   before save  default values   def default values     self status      P    end end

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The Phusion guys have some nice plugin for this

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use default scope in rails 3  api doc  ActiveRecord obscures the difference between defaulting defined in the database  schema  and defaulting done in the application  model   During initialization  it parses the database schema and notes any default values specified there  Later  when creating objects  it assigns those schema-specified default values without touching the database   discussion

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I use the attribute-defaults gem  From the documentation  run sudo gem install attribute-defaults and add require  attribute defaults  to your app   class Foo  lt  ActiveRecord  Base   attr default  age  18   attr default  last seen do     Time now   end end  Foo new                 gt  age  18  last seen   gt   2014-10-17 09 44 27  Foo new  age   gt  25      gt  age  25  last seen   gt   2014-10-17 09 44 28

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We put the default values in the database through migrations  by specifying the  default option on each column definition  and let Active Record use these values to set the default for each attribute   IMHO  this approach is aligned with the principles of AR   convention over configuration  DRY  the table definition drives the model  not the other way around   Note that the defaults are still in the application  Ruby  code  though not in the model but in the migration s

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The after initialize callback pattern can be improved by simply doing the following  after initialize  some method goes here   if   gt   new record    This has a non-trivial benefit if your init code needs to deal with associations  as the following code triggers a subtle n 1 if you read the initial record without including the associated   class Account    has one  config   after initialize  init config    def init config     self config     build config   end  end

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class Item  lt  ActiveRecord  Base   def status     self  status  or ACTIVE   end    before save  self status     ACTIVE   end

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This is what constructors are for  Override the model s initialize method   Use the after initialize method

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Rails 5  You can use the attribute method within your models  eg   class Account  lt  ApplicationRecord   attribute  locale   string  default   en  end   You can also pass a lambda to the default parameter  Example  attribute  uuid   string  default  - gt    SecureRandom uuid    The second argument is the type and it can also be a custom type class instance  for example  attribute  uuid  UuidType new  default  - gt    SecureRandom uuid

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The problem with the after initialize solutions is that you have to add an after initialize to every single object you look up out of the DB  regardless of whether you access this attribute or not  I suggest a lazy-loaded approach    The attribute methods  getters  are of course methods themselves  so you can override them and provide a default  Something like   Class Foo  lt  ActiveRecord  Base     has a DB column field atttribute called  status    def status      val   read attribute  status   nil     ACTIVE    val   end end   Unless  like someone pointed out  you need to do Foo find by status  ACTIVE    In that case I think you d really need to set the default in your database constraints  if the DB supports it

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I ran into problems with after initialize giving ActiveModel  MissingAttributeError errors when doing complex finds   eg    bottles   Bottle includes  supplier   substance  where search  order  suppliers name ASC   paginate  page   gt  page no     search  in the  where is hash of conditions  So I ended up doing it by overriding initialize in this way   def initialize   super   default values end  private  def default values      self date received     Date current  end   The super call is necessary to make sure the object initializing correctly from ActiveRecord  Base before doing my customize code  ie  default values

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Been using this for a while    post rb class Post  lt  ApplicationRecord   attribute  country   string  default   ID  end

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Here s a solution I ve used that I was a little surprised hasn t been added yet    There are two parts to it   First part is setting the default in the actual migration  and the second part is adding a validation in the model ensuring that the presence is true     add column  teams   new team signature   string  default   Welcome to the Team    So you ll see here that the default is already set   Now in the validation you want to ensure that there is always a value for the string  so just do   validates  new team signature  presence  true   What this will do is set the default value for you   for me I have  Welcome to the Team    and then it will go one step further an ensure that there always is a value present for that object    Hope that helps

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Although doing that for setting default values is confusing and awkward in most cases  you can use  default scope as well  Check out squil s comment here

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class Item  lt  ActiveRecord  Base   def status     self  status  or ACTIVE   end    before save  self status     ACTIVE   end

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I had a similar challenge when working on a Rails 6 application  Here s how I solved it  I have a Users table and a Roles table  The Users table belongs to the Roles table  I also have an Admin and Student Models that inherit from the Users table  It then required that I set a default value for the role whenever a user is created  say admin role that has an id   1 or student role that has an id   2  class User  Admin  lt  User   before save  default values    def default values       set role id to  1  except if role id is not empty     return self role id    1  unless role id nil    end end  This means that before an admin user is created saved in the database the role id is set to a default of 1 if it is not empty  return self role id    1  unless role id nil    is the same as  return self role id    1  unless self role id nil   and the same as  self role id    1  if role id nil   but the first one is cleaner and more precise  That s all  I hope this helps

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This is what constructors are for  Override the model s initialize method   Use the after initialize method

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I ve found that using a validation method provides a lot of control over setting defaults  You can even set defaults  or fail validation  for updates  You even set a different default value for inserts vs updates if you really wanted to  Note that the default won t be set until  valid  is called   class MyModel   validate  init defaults    private   def init defaults     if new record        self some int     1     elsif some int nil        errors add  some int   can t be blank on update       end   end end   Regarding defining an after initialize method  there could be performance issues because after initialize is also called by each object returned by  find   http   guides rubyonrails org active record validations callbacks html after initialize-and-after find

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An even better cleaner potential way than the answers proposed is to overwrite the accessor  like this   def status   self  status      ACTIVE end   See  Overwriting default accessors  in the ActiveRecord  Base documentation and more from StackOverflow on using self

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An even better cleaner potential way than the answers proposed is to overwrite the accessor  like this   def status   self  status      ACTIVE end   See  Overwriting default accessors  in the ActiveRecord  Base documentation and more from StackOverflow on using self

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use default scope in rails 3  api doc  ActiveRecord obscures the difference between defaulting defined in the database  schema  and defaulting done in the application  model   During initialization  it parses the database schema and notes any default values specified there  Later  when creating objects  it assigns those schema-specified default values without touching the database   discussion

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Sup guys  I ended up doing the following   def after initialize   self extras       self other stuff    This stuff  end   Works like a charm

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Although doing that for setting default values is confusing and awkward in most cases  you can use  default scope as well  Check out squil s comment here

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I ve also seen people put it in their migration  but I d rather see it   defined in the model code       Is there a canonical way to set default value for fields in   ActiveRecord model    The canonical Rails way  before Rails 5  was actually to set it in the migration  and just look in the db schema rb for whenever wanting to see what default values are being set by the DB for any model    Contrary to what  Jeff Perrin answer states  which is a bit old   the migration approach will even apply the default when using Model new  due to some Rails magic  Verified working in Rails 4 1 16   The simplest thing is often the best  Less knowledge debt and potential points of confusion in the codebase  And it  just works    class AddStatusToItem  lt  ActiveRecord  Migration   def change     add column  items   scheduler type   string    null  false  default   hotseat      end end   Or  for column change without creating a new one  then do either   class AddStatusToItem  lt  ActiveRecord  Migration   def change     change column default  items   scheduler type   hotseat    end end   Or perhaps even better   class AddStatusToItem  lt  ActiveRecord  Migration   def change     change column  items   scheduler type   string  default   hotseat    end end   Check the official RoR guide for options in column change methods   The null  false disallows NULL values in the DB  and  as an added benefit  it also updates so that all pre-existing DB records that were previously null is set with the default value for this field as well  You may exclude this parameter in the migration if you wish  but I found it very handy   The canonical way in Rails 5  is  as  Lucas Caton said   class Item  lt  ActiveRecord  Base   attribute  scheduler type   string  default   hotseat  end

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after initialize method is deprecated  use the callback instead   after initialize  defaults  def defaults   self extras        self other stuff    This stuff  end   however  using  default in your migrations is still the cleanest way

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This has been answered for a long time  but I need default values frequently and prefer not to put them in the database  I create a DefaultValues concern   module DefaultValues   extend ActiveSupport  Concern    class methods do     def defaults attr  to  nil  on   initialize        method name    set default   attr         send  after   on    method name to sym        define method method name  do         if send attr            send attr          else           value   to is a  Proc    to call   to           send    attr     value          end       end        private method name     end   end end   And then use it in my models like so   class Widget  lt  ApplicationRecord   include DefaultValues    defaults  category  to   uncategorized    defaults  token  to  - gt    SecureRandom uuid   end

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Similar questions  but all have slightly different context  - How do I create a default value for attributes in Rails activerecord  39 s model   Best Answer  Depends on What You Want   If you want every object to start with a value  use after initialize  init  You want the new html form to have a default value upon opening the page  use https   stackoverflow com a 5127684 1536309  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    If you want every object to have a value calculated from user input  use before save  default values You want user to enter X and then Y   X  foo   use   class Task  lt  ActiveRecord  Base   before save  default values   def default values     self status      P    end end

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If the column happens to be a  status  type column  and your model lends itself to the use of state machines  consider using the aasm gem  after which you can simply do     aasm column   status  do     state  available  initial  true     state  used       transitions   end   It still doesn t initialize the value for unsaved records  but it s a bit cleaner than rolling your own with init or whatever  and you reap the other benefits of aasm such as scopes for all your statuses

User · Answer

after initialize method is deprecated  use the callback instead   after initialize  defaults  def defaults   self extras        self other stuff    This stuff  end   however  using  default in your migrations is still the cleanest way

User · Answer

I ran into problems with after initialize giving ActiveModel  MissingAttributeError errors when doing complex finds   eg    bottles   Bottle includes  supplier   substance  where search  order  suppliers name ASC   paginate  page   gt  page no     search  in the  where is hash of conditions  So I ended up doing it by overriding initialize in this way   def initialize   super   default values end  private  def default values      self date received     Date current  end   The super call is necessary to make sure the object initializing correctly from ActiveRecord  Base before doing my customize code  ie  default values

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Rails 5  You can use the attribute method within your models  eg   class Account  lt  ApplicationRecord   attribute  locale   string  default   en  end   You can also pass a lambda to the default parameter  Example  attribute  uuid   string  default  - gt    SecureRandom uuid    The second argument is the type and it can also be a custom type class instance  for example  attribute  uuid  UuidType new  default  - gt    SecureRandom uuid

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I strongly suggest using the  default value for  gem  https   github com FooBarWidget default value for  There are some tricky scenarios that pretty much require overriding the initialize method  which that gem does   Examples   Your db default is NULL  your model ruby-defined default is  some string   but you actually want to set the value to nil for whatever reason  MyModel new my attr  nil   Most solutions here will fail to set the value to nil  and will instead set it to the default   OK  so instead of taking the     approach  you switch to my attr changed      BUT now imagine your db default is  some string   your model ruby-defined default is  some other string   but under a certain scenario  you want to set the value to  some string   the db default   MyModel new my attr   some string    This will result in my attr changed  being false because the value matches the db default  which in turn will fire your ruby-defined default code and set the value to  some other string  -- again  not what you desired     For those reasons I don t think this can properly be accomplished with just an after initialize hook   Again  I think the  default value for  gem is taking the right approach  https   github com FooBarWidget default value for

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https   github com keithrowell rails default value  class Task  lt  ActiveRecord  Base   default  status   gt   active  end

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The Phusion guys have some nice plugin for this

User · Answer

I ve also seen people put it in their migration  but I d rather see it   defined in the model code       Is there a canonical way to set default value for fields in   ActiveRecord model    The canonical Rails way  before Rails 5  was actually to set it in the migration  and just look in the db schema rb for whenever wanting to see what default values are being set by the DB for any model    Contrary to what  Jeff Perrin answer states  which is a bit old   the migration approach will even apply the default when using Model new  due to some Rails magic  Verified working in Rails 4 1 16   The simplest thing is often the best  Less knowledge debt and potential points of confusion in the codebase  And it  just works    class AddStatusToItem  lt  ActiveRecord  Migration   def change     add column  items   scheduler type   string    null  false  default   hotseat      end end   Or  for column change without creating a new one  then do either   class AddStatusToItem  lt  ActiveRecord  Migration   def change     change column default  items   scheduler type   hotseat    end end   Or perhaps even better   class AddStatusToItem  lt  ActiveRecord  Migration   def change     change column  items   scheduler type   string  default   hotseat    end end   Check the official RoR guide for options in column change methods   The null  false disallows NULL values in the DB  and  as an added benefit  it also updates so that all pre-existing DB records that were previously null is set with the default value for this field as well  You may exclude this parameter in the migration if you wish  but I found it very handy   The canonical way in Rails 5  is  as  Lucas Caton said   class Item  lt  ActiveRecord  Base   attribute  scheduler type   string  default   hotseat  end

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Here s a solution I ve used that I was a little surprised hasn t been added yet    There are two parts to it   First part is setting the default in the actual migration  and the second part is adding a validation in the model ensuring that the presence is true     add column  teams   new team signature   string  default   Welcome to the Team    So you ll see here that the default is already set   Now in the validation you want to ensure that there is always a value for the string  so just do   validates  new team signature  presence  true   What this will do is set the default value for you   for me I have  Welcome to the Team    and then it will go one step further an ensure that there always is a value present for that object    Hope that helps

User · Answer

The Phusion guys have some nice plugin for this

User · Answer

We put the default values in the database through migrations  by specifying the  default option on each column definition  and let Active Record use these values to set the default for each attribute   IMHO  this approach is aligned with the principles of AR   convention over configuration  DRY  the table definition drives the model  not the other way around   Note that the defaults are still in the application  Ruby  code  though not in the model but in the migration s

User · Answer

This is what constructors are for  Override the model s initialize method   Use the after initialize method

User · Answer

There are several issues with each of the available methods  but I believe that defining an after initialize callback is the way to go for the following reasons    default scope 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 not what you want  Defining defaults in your migration also works part of the time    As has already been mentioned this will not work when you just call Model new  Overriding initialize can work  but don t forget to call super  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  Overriding after initialize is deprecated as of Rails 3  When I override after initialize in rails 3 0 3 I get the following warning in the console       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    Therefore I d say write an after initialize callback  which lets you default attributes in addition to letting you set defaults on associations like so     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       Now you have just one place to look for initialization of your models  I m using this method until someone comes up with a better one   Caveats    For boolean fields do   self bool field   true if self bool field nil   See Paul Russell s comment on this answer for more details If you re only selecting a subset of columns for a model  ie  using select in a query like Person select  firstname   lastname  all  you will get a MissingAttributeError if your init method accesses a column that hasn t been included in the select clause  You can guard against this case like so   self number     0 0 if self has attribute   number  and for a boolean column     self bool field   true if  self has attribute   bool value   amp  amp  self bool field nil   Also note that the syntax is different prior to Rails 3 2  see Cliff Darling s comment below

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From the api docs http   api rubyonrails org classes ActiveRecord Callbacks html Use the before validation method in your model  it gives you the options of creating specific initialisation for create and update calls e g  in this example  again code taken from the api docs example  the number field is initialised for a credit card  You can easily adapt this to set whatever values you want  class CreditCard  lt  ActiveRecord  Base     Strip everything but digits  so the user can specify  555 234 34  or      5552-3434  or both will mean  55523434    before validation  on   gt   create  do     self number   number gsub  r  0-9        if attribute present   number     end end  class Subscription  lt  ActiveRecord  Base   before create  record signup    private     def record signup       self signed up on   Date today     end end  class Firm  lt  ActiveRecord  Base     Destroys the associated clients and people when the firm is destroyed   before destroy    record  Person destroy all  firm id     record id         before destroy    record  Client destroy all  client of     record id     end   Surprised that his has not been suggested here

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Some simple cases can be handled by defining a default in the database schema but that doesn t handle a number of trickier cases including calculated values and keys of other models  For these cases I do this   after initialize  defaults  def defaults    unless persisted      self extras          self other stuff    This stuff      self assoc    OtherModel find by name  special      end end   I ve decided to use the after initialize but I don t want it to be applied to objects that are found only those new or created   I think it is almost shocking that an after new callback isn t provided for this obvious use case but I ve made do by confirming whether the object is already persisted indicating that it isn t new   Having seen Brad Murray s answer this is even cleaner if the condition is moved to callback request   after initialize  defaults  unless   persisted                    if   gt   new record   is equivalent in this context  def defaults   self extras        self other stuff    This stuff    self assoc    OtherModel find by name  special    end

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I had a similar challenge when working on a Rails 6 application  Here s how I solved it  I have a Users table and a Roles table  The Users table belongs to the Roles table  I also have an Admin and Student Models that inherit from the Users table  It then required that I set a default value for the role whenever a user is created  say admin role that has an id   1 or student role that has an id   2  class User  Admin  lt  User   before save  default values    def default values       set role id to  1  except if role id is not empty     return self role id    1  unless role id nil    end end  This means that before an admin user is created saved in the database the role id is set to a default of 1 if it is not empty  return self role id    1  unless role id nil    is the same as  return self role id    1  unless self role id nil   and the same as  self role id    1  if role id nil   but the first one is cleaner and more precise  That s all  I hope this helps

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Some simple cases can be handled by defining a default in the database schema but that doesn t handle a number of trickier cases including calculated values and keys of other models  For these cases I do this   after initialize  defaults  def defaults    unless persisted      self extras          self other stuff    This stuff      self assoc    OtherModel find by name  special      end end   I ve decided to use the after initialize but I don t want it to be applied to objects that are found only those new or created   I think it is almost shocking that an after new callback isn t provided for this obvious use case but I ve made do by confirming whether the object is already persisted indicating that it isn t new   Having seen Brad Murray s answer this is even cleaner if the condition is moved to callback request   after initialize  defaults  unless   persisted                    if   gt   new record   is equivalent in this context  def defaults   self extras        self other stuff    This stuff    self assoc    OtherModel find by name  special    end

User · Answer

db schema rb create table  store listings  force  true do  t    t string  my string  default   original default  end  StoreListing new my string     gt   original default     app models store listing rb class StoreListing  lt  ActiveRecord  Base   attribute  my string   string  default   new default  end  StoreListing new my string     gt   new default   class Product  lt  ActiveRecord  Base   attribute  my default proc   datetime  default  - gt    Time now   end  Product new my default proc     gt  2015-05-30 11 04 48 -0600 sleep 1 Product new my default proc     gt  2015-05-30 11 04 49 -0600

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class Item  lt  ActiveRecord  Base   def status     self  status  or ACTIVE   end    before save  self status     ACTIVE   end

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The after initialize callback pattern can be improved by simply doing the following  after initialize  some method goes here   if   gt   new record    This has a non-trivial benefit if your init code needs to deal with associations  as the following code triggers a subtle n 1 if you read the initial record without including the associated   class Account    has one  config   after initialize  init config    def init config     self config     build config   end  end

[ruby-on-rails] Rails: How can I set default values in ActiveRecord?

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