In my application, I have a class called Budget. The budget can be of many types.. For instance, let's say that there are two budgets: FlatRateBudget and HourlyRateBudget. Both inherit from the class Budget.
This is what I get so far:
class Budget < ActiveRecord::Base
validates_presence_of :price
end
class FlatRateBudget < Budget
end
class HourlyRateBudget < Budget
validates_presence_of :quantity
end
In the console, if I do:
b = HourlyRateBudget.new(:price => 10)
b.valid?
=> false
b.errors.full_messages
=> ["Quantity can't be blank"]
As, expected.
The problem is that the "type" field, on STI, comes from params.. So i need to do something like:
b = Budget.new(:type => "HourlyRateBudget", :price => 10)
b.valid?
=> true
Which means that rails is running validations in the super-class instead of instantiating the sub class after I set up the type.
I know that is the expected behaviour, since I'm instantiating a class that dosen't need the quantity field, but I wonder if there is anyway to tell rails to run the validations for the subclass instead of the super.
You could probably solve this with a custom validator, similar to the answer on this question: Two models, one STI and a Validation However, if you can simply instantiate the intended sub-type to begin with, you would avoid the need for a custom validator altogether in this case.
As you've noticed, setting the type field alone doesn't magically change an instance from one type to another. While ActiveRecord will use the type field to instantiate the proper class upon reading the object from the database, doing it the other way around (instantiating the superclass, then changing the type field manually) doesn't have the effect of changing the object's type while your app is running - it just doesn't work that way.
The custom validation method, on the other hand, could check the type field independently, instantiate a copy of the appropriate type (based on the value of the type field), and then run .valid? on that object, resulting in the validations on the sub-class being run in a way that appears to be dynamic, even though it's actually creating an instance of the appropriate sub-class in the process.
I've done something similar.
Adapting it to your problem:
class Budget < ActiveRecord::Base
validates_presence_of :price
validates_presence_of :quantity, if: :hourly_rate?
def hourly_rate?
self.class.name == 'HourlyRateBudget'
end
end
For anyone looking for example code, here's how I implemented the first answer:
validate :subclass_validations
def subclass_validations
# Typecast into subclass to check those validations
if self.class.descends_from_active_record?
subclass = self.becomes(self.type.classify.constantize)
self.errors.add(:base, "subclass validations are failing.") unless subclass.valid?
end
end
Instead of setting the type directly set the type like that... Instead, try:
new_type = params.fetch(:type)
class_type = case new_type
when "HourlyRateBudget"
HourlyRateBudget
when "FlatRateBudget"
FlatRateBudget
else
raise StandardError.new "unknown budget type: #{new_type}"
end
class_type.new(:price => 10)
You could even transform the string into its class by:
new_type.classify.constantize but if it's coming in from params, that seems a bit dangerous.
If you do this, then you'll get a class of HourlyRateBudget, otherwise it'll just be Budget.
Better yet, use type.constantize.new("10"), however this depends on that the type from params must be correct string identical to HourlyRateBudget.class.to_s
I also required the same and with the help of Bryce answer i did this:
class ActiveRecord::Base
validate :subclass_validations, :if => Proc.new{ is_sti_supported_table? }
def is_sti_supported_table?
self.class.columns_hash.include? (self.class.inheritance_column)
end
def subclass_validations
subclass = self.class.send(:compute_type, self.type)
unless subclass == self.class
subclass_obj= self.becomes(subclass)
self.errors.add(:base, subclass_obj.errors.full_messages.join(', ')) unless subclass_obj.valid?
end
end
end
Along the lines of #franzlorenzon's answer, but using duck typing to avoid referencing class type in the super class:
class Budget < ActiveRecord::Base
validates_presence_of :price
validates_presence_of :quantity, if: :hourly_rate?
def hourly_rate?
false
end
end
class HourlyRateBudget < Budget
def hourly_rate?
true
end
end
What is the correct way to refer to current_user.user_profile.name when there may or may not be a user_profile record for a particular user?
I have two tables, User (:email) and UserProfile (:name, :company).
User has_one user_profile, and UserProfile belongs_to User
A profile may or may not not exist. (It's optional for users)
In lot of my code and views I want to display the user's name and company, for example current_user.user_profile.name
Of course, if the user has not created their profile yet, current_user.user_profile is nil, so referencing current_user.user_profile.name throws an error.
I know how to do it the wrong way (check for nil before referencing the .name field EVERY time I need the name).
The best I can think of is create a User method called name that does the nil checking so current_user.name returns the name (or "" if there is no profile). But that feels wrong, too, since I have to write a method for every single field I add to user_profile.
I agree with the Law of Demeter answers, but Rails has a convenient way for your User class to delegate :name and other methods to its user_profile:
class User < ActiveRecord::Base
has_one :user_profile
delegate :name, :email, :phone, :height, :etc,
to: :user_profile, allow_nil: true, prefix: :profile
end
Now these:
user.profile_name
user.profile_email
user.profile_phone
will return nil if user.user_profile is nil, and otherwise return user.user_profile.name, user.user_profile.email, and user.user_profile.phone, respectively. But they hide that fact from callers, who only interact with User. You could leave off the prefix option if you'd rather have this:
user.name
user.email
user.phone
In general I'd shy away from strategies that involve exceptions or rescue, unless a nil user_profile is truly something that should not happen. And I'd hate to use andand or try because they push the responsibility of managing the user_profile to callers.
You could do something like this that should work with all attributes of the UserProfile:
# User.rb
def try_this(attribute)
self.user_profile ? self.user_profile.send(attribute) : "Not Available"
end
Then you'd just call
current_user.try_this(:name)
Edit
Dylan's try method also works:
def try_this(attribute)
self.user_profile.try(attribute) || "Not Available"
end
You could use try:
current_user.user_profile.try(:name) || "Not Available"
When you use rescue, there's a risk that you may be rescuing from a different type of error than NoMethodError as a result of user_profile being nil.
current_user.andand.user_profile.name || "Not Available"
The "andand" gem implements null-safe chaining.
As you suggest, creating a User.name method may be preferable (and Demeter would be proud).
You are correct. The best way, according to the Law of Demeter, is to add a method on User with this logic. Whatever needs the user's name shouldn't need to know about user_profile.
Each unit should have only limited knowledge about other units: only units "closely" related to the current unit.
So...
class User < ActiveRecord::Base
def user_name
user_profile ? user_profile.name : ""
end
[...]
end
current_user.user_profile.name rescue "Not Available"
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