Hey all -- this question is specifically about a gender validation, but I'm interested in hearing how you've all handled similar situations with much larger collections (Country selection, for example.)
I'm working on a system that lets athletes register for various events, and am currently working on a good gender validation. My question is, what's the best, most DRY way to run the same validation on many different models?
Let's say I want to validate the gender property of Event and User. I can create a helper for validates_each that checks values for inclusion in the very short array of ["male", "female"] before updating the gender attribute. But what if I want to access this same gender array in a form_for block, say, as an input to collection_select?
I have it working for one model -- I declare a GENDERS constant in Event, and have a short class method
def self.genders
GENDERS
end
for access by forms. But where should I store the array if multiple models need access?
EDIT: One idea would be to use a class method in the application controller. Any thoughts on how appropriate this approach is would be great.
Here's my solution. I like to go with the standard plugin-style libraries. I'd put this in lib/acts_as_gendered:
module ActsAsGendered
GENDERS = ['male', 'female']
def self.included(base)
base.extend(ActsAsGenderedMethods)
end
module ActsAsGenderedMethods
def acts_as_gendered
extend ClassMethods
include InstanceMethods
validates_inclusion_of :gender, :in => GENDERS
end
end
module ClassMethods
def is_gendered?
true
end
end
module InstanceMethods
def is_male
gender = 'male'
end
def is_female
gender = 'female'
end
def is_male?
gender == 'male'
end
def is_female?
gender == 'female'
end
end
end
Yeah, it might be overkill for simple genders, but you can see where all the pieces go - the GENDERS constant, the acts_as_gendered ActiveRecord hook, which then includes the class and instance methods and the validation.
Then, in config/initializers/gender.rb:
require 'acts_as_gendered'
ActiveRecord::Base.send(:include, ActsAsGendered)
Then, for the grand finale, the model:
class User < ActiveRecord::Base
acts_as_gendered
end
This pattern may seem overly complicated, but that's how most libraries end up eventually :)
UPDATE: To answer your comment, this is how I'd modify the acts_as_gendered method to make validations optional on a per-model basis:
def acts_as_gendered options={}
config = {:allow_nil => false}
config.merge(options) if options.is_a?(Hash)
extend ClassMethods
include InstanceMethods
if config[:allow_nil]
validates_inclusion_of :gender, :in => (GENDERS + nil)
else
validates_inclusion_of :gender, :in => GENDERS
end
end
Now you can call it in the User model like this:
class User < ActiveRecord::Base
acts_as_gendered :allow_nil => true
end
I could have made it a simple parameter you pass in, but I like the clarity of passing in a hash. And it sets you up for adding other options down the road.
You've got the right idea by storing it in a constant. The only thing I would do differently is put it in an initializer file so that it's not tied to any particular model like it is in your example. If you're worried about potential name collisions at the top level, you could put it in a module in the lib directory and include the module only in the places you intend to use it.
I agree with putting this in a constant. I'd also put the strings themselves in constants because (1) they can change, and (2) when used in a conditional, the system will catch if you mistype them. E.g., in your environment.rb:
MALE = 'male'
FEMALE = 'female'
GENDERS = [MALE, FEMALE]
And then in your code, you only ever refer to these constants, e.g.:
def male?
return gender == MALE
end
I would write a custom validation plugin (say, validates_gender). Then you would call:
class Event < ActiveRecord::Base
validates_gender :gender
end
Grab a copy of my validates_as_email plugin and use that, replacing value =~ EMAIL_ADDRESS_RE with your own logic.
I want to create a Rails (2.1 and 2.2) model with ActiveRecord validations, but without a database table. What is the most widely used approach? I've found some plugins that claim to offer this functionality, but many of them don't appear to be widely used or maintained. What does the community recommend I do? Right now I am leaning toward coming up with my own solution based on this blog post.
There is a better way to do this in Rails 3: http://railscasts.com/episodes/219-active-model
This is an approach I have used in the past:
In app/models/tableless.rb
class Tableless < ActiveRecord::Base
def self.columns
#columns ||= [];
end
def self.column(name, sql_type = nil, default = nil, null = true)
columns << ActiveRecord::ConnectionAdapters::Column.new(name.to_s, default,
sql_type.to_s, null)
end
# Override the save method to prevent exceptions.
def save(validate = true)
validate ? valid? : true
end
end
In app/models/foo.rb
class Foo < Tableless
column :bar, :string
validates_presence_of :bar
end
In script/console
Loading development environment (Rails 2.2.2)
>> foo = Foo.new
=> #<Foo bar: nil>
>> foo.valid?
=> false
>> foo.errors
=> #<ActiveRecord::Errors:0x235b270 #errors={"bar"=>["can't be blank"]}, #base=#<Foo bar: nil>>
There is easier way now:
class Model
include ActiveModel::Model
attr_accessor :var
validates :var, presence: true
end
ActiveModel::Model code:
module ActiveModel
module Model
def self.included(base)
base.class_eval do
extend ActiveModel::Naming
extend ActiveModel::Translation
include ActiveModel::Validations
include ActiveModel::Conversion
end
end
def initialize(params={})
params.each do |attr, value|
self.public_send("#{attr}=", value)
end if params
end
def persisted?
false
end
end
end
http://api.rubyonrails.org/classes/ActiveModel/Model.html
I think the blog post you are linking is the best way to go. I would only suggest moving the stubbed out methods into a module not to pollute your code.
just create a new file ending in ".rb" following the conventions you're used to (singular for file name and class name, underscored for file name, camel case for class name) on your "models/" directory. The key here is to not inherit your model from ActiveRecord (because it is AR that gives you the database functionality).
e.g.: for a new model for cars, create a file called "car.rb" in your models/ directory and inside your model:
class Car
# here goes all your model's stuff
end
edit: btw, if you want attributes on your class, you can use here everything you use on ruby, just add a couple lines using "attr_accessor":
class Car
attr_accessor :wheels # this will create for you the reader and writer for this attribute
attr_accessor :doors # ya, this will do the same
# here goes all your model's stuff
end
edit #2: after reading Mike's comment, I'd tell you to go his way if you want all of the ActiveRecord's functionality but no table on the database. If you just want an ordinary Ruby class, maybe you'll find this solution better ;)
For the sake of completeness:
Rails now (at V5) has a handy module you can include:
include ActiveModel::Model
This allows you to initialise with a hash, and use validations amongst other things.
Full documentation is here.
There's a screencast about non-Active Record model, made up by Ryan Bates. A good place to start from.
Just in case you did not already watch it.
I have built a quick Mixin to handle this, as per John Topley's suggestion.
http://github.com/willrjmarshall/Tableless
What about marking the class as abstract?
class Car < ActiveRecord::Base
self.abstract = true
end
this will tell rails that the Car class has no corresponding table.
[edit]
this won't really help you if you'll need to do something like:
my_car = Car.new
Use the Validatable gem. As you say, there are AR-based solutions, but they tend to be brittle.
http://validatable.rubyforge.org/
Anybody has ever tried to include ActiveRecord::Validations and ActiveRecord::Validations::ClassMethods in a non-Active Record class and see what happens when trying to setup validators ?
I'm sure there are plenty of dependencies between the validation framework and ActiveRecord itself. But you may succeed in getting rid of those dependencies by forking your own validation framework from the AR validation framework.
Just an idea.
Update: oopps, this is more or less what's suggested in the post linked with your question. Sorry for the disturbance.
Do like Tiago Pinto said and just don't have your model inherit from ActiveRecord::Base. It'll just be a regular Ruby class that you stick in a file in your app/models/ directory. If none of your models have tables and you're not using a database or ActiveRecord at all in your app, be sure to modify your environment.rb file to have the following line:
config.frameworks -= [:active_record]
This should be within the Rails::Initializer.run do |config| block.
You ought to checkout the PassiveRecord plugin. It gives you an ActiveRecord-like interface for non-database models. It's simple, and less hassle than fighting ActiveRecord.
We're using PassiveRecord in combination with the Validatable gem to get the OP's desired behaviour.
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 < ActiveRecord::Base
def initialize_with_defaults(attrs = nil, &block)
initialize_without_defaults(attrs) do
setter = lambda { |key, value| self.send("#{key.to_s}=", value) unless
!attrs.nil? && attrs.keys.map(&: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?
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 < 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) && self.bool_field.nil?
Also note that the syntax is different prior to Rails 3.2 (see Cliff Darling's comment below)
Rails 5+
You can use the attribute method within your models, eg.:
class Account < ApplicationRecord
attribute :locale, :string, default: 'en'
end
You can also pass a lambda to the default parameter. Example:
attribute :uuid, :string, default: -> { 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: -> { SecureRandom.uuid }
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).
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 => :new_record?" is equivalent in this context
def defaults
self.extras||={}
self.other_stuff||="This stuff"
self.assoc = [OtherModel.find_by_name('special')]
end
The after_initialize callback pattern can be improved by simply doing the following
after_initialize :some_method_goes_here, :if => :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
The Phusion guys have some nice plugin for this.
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.
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 < ActiveRecord::Base
attr_default :age, 18
attr_default :last_seen do
Time.now
end
end
Foo.new() # => age: 18, last_seen => "2014-10-17 09:44:27"
Foo.new(:age => 25) # => age: 25, last_seen => "2014-10-17 09:44:28"
Similar questions, but all have slightly different context:
- How do I create a default value for attributes in Rails activerecord'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 < 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 < ActiveRecord::Base
before_save :default_values
def default_values
self.status ||= 'P'
end
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?
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 < 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 < ActiveRecord::Migration
def change
change_column_default :items, :scheduler_type, "hotseat"
end
end
Or perhaps even better:
class AddStatusToItem < 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 < ActiveRecord::Base
attribute :scheduler_type, :string, default: 'hotseat'
end
This is what constructors are for! Override the model's initialize method.
Use the after_initialize method.
Sup guys, I ended up doing the following:
def after_initialize
self.extras||={}
self.other_stuff||="This stuff"
end
Works like a charm!
Rails 6.1+
You can now use the attribute method on your model without setting a type.
attribute :status, default: ACTIVE
or
class Account < ApplicationRecord
attribute :locale, default: 'en'
end
Note that feeding a default to attribute cannot reference the instance of the class (a lambda will execute in the context of the class, not the instance). So, if you need to set the default to a value dynamically based on the instance or associations, you're still going to have to use an alternative, such as an after_initialize callback. As stated previously, it's recommended to limit this to new records only to avoid n+1 queries if you reference associations.
after_initialize :do_something_that_references_instance_or_associations, if: :new_record?
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 < ApplicationRecord
include DefaultValues
defaults :category, to: 'uncategorized'
defaults :token, to: -> { SecureRandom.uuid }
end
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 => 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
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.
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 < 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.
class Item < ActiveRecord::Base
def status
self[:status] or ACTIVE
end
before_save{ self.status ||= ACTIVE }
end
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
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.
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
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.
https://github.com/keithrowell/rails_default_value
class Task < ActiveRecord::Base
default :status => 'active'
end
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!
# db/schema.rb
create_table :store_listings, force: true do |t|
t.string :my_string, default: "original default"
end
StoreListing.new.my_string # => "original default"
# app/models/store_listing.rb
class StoreListing < ActiveRecord::Base
attribute :my_string, :string, default: "new default"
end
StoreListing.new.my_string # => "new default"
class Product < ActiveRecord::Base
attribute :my_default_proc, :datetime, default: -> { Time.now }
end
Product.new.my_default_proc # => 2015-05-30 11:04:48 -0600
sleep 1
Product.new.my_default_proc # => 2015-05-30 11:04:49 -0600
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 < 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
Been using this for a while.
# post.rb
class Post < ApplicationRecord
attribute :country, :string, default: 'ID'
end
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
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 < 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 => :create) do
self.number = number.gsub(%r[^0-9]/, "") if attribute_present?("number")
end
end
class Subscription < ActiveRecord::Base
before_create :record_signup
private
def record_signup
self.signed_up_on = Date.today
end
end
class Firm < 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