I have a trashable concern that allows a user to trash ("delete") certain things.
The issue is that even though that item can be trashed, it still has to be referenced if you view something older. If you do that now it won't find that object as I've changed the default_scope to only show where trashed is false.
Here's my trashable module:
module Trashable
extend ActiveSupport::Concern
included do
default_scope { where(trashed: false) }
scope :trashed, -> { unscoped.where(trashed: true) }
validates :trashed, inclusion: { in: [true, false] }
end
def trash
update_attribute :trashed, true
end
end
now I have an Order model, where you can view an order. If we for example trash a product, I still want the user to be able to look at their order and see the product.
Now I'm not able to access that with a model association such as:
has_many :products and make it so that it includes both where trashed is false and true.
Does anybody know how to achieve this?
You can achieve this by several ways, here is what I know
Solution 1 Define with_trashed like this:
module Trashable
extend ActiveSupport::Concern
included do
default_scope { where(trashed: false) }
scope :trashed, -> { unscoped.where(trashed: true) }
# Define a new scope here
scope :with_trashed, -> { unscope(where: :trashed) }
validates :trashed, inclusion: { in: [true, false] }
end
def trash
update_attribute :trashed, true
end
end
Then you can use it like:
order.products.with_trashed
Solution 2 Define unscoped class
class UnscopedProduct < Product
self.default_scopes = []
belongs_to :order
end
class Order < ActiveRecord::Base
has_many :products
has_many :unscoped_products, foreign_key: :order_id, class_name: "UnscopedProduct"
end
Then you can use it like:
order.unscope_products
As my experience, I would use Solution 1, but there are some weird cases, this doesn't work anymore, for example, in a complex query, so remember solution 2, it will save a lot of time!
Using Default scope will lead to so many problems for later complex queries. That depends on you!
You can do a couple of things:
As someone mentioned in the comment, you should use Acts as Paranoid Gem that is exactly meant for this purpose. Using that, you can use methods with_deleted or only_deleted that will return you relevant deleted objects as well.
You cannot simply use unscoped as you are doing above. Unscoped will remove all the conditions and not only trashed: false. You can also try to create another scope which returns you deleted objects and merge the objects found in the second scope with the first one.
scope_1_results + scope_2_results
If you are on Rails 5, you can also OR the scopes which is not possible in Rails 4.x or less.
I'd like to create a callback function in rails that executes after a model is saved.
I have this model, Claim that has a attribute 'status' which changes depending on the state of the claim, possible values are pending, endorsed, approved, rejected
The database has 'state' with the default value of 'pending'.
I'd like to perform certain tasks after the model is created on the first time or updated from one state to another, depending on which state it changes from.
My idea is to have a function in the model:
after_save :check_state
def check_state
# if status changed from nil to pending (created)
do this
# if status changed from pending to approved
performthistask
end
My question is how do I check for the previous value before the change within the model?
You should look at ActiveModel::Dirty module:
You should be able to perform following actions on your Claim model:
claim.status_changed? # returns true if 'status' attribute has changed
claim.status_was # returns the previous value of 'status' attribute
claim.status_change # => ['old value', 'new value'] returns the old and
# new value for 'status' attribute
claim.name = 'Bob'
claim.changed # => ["name"]
claim.changes # => {"name" => ["Bill", "Bob"]}
Oh! the joys of Rails!
you can use this
self.changed
it return an array of all columns that changed in this record
you can also use
self.changes
which returns a hash of columns that changed and before and after results as arrays
For Rails 5.1+, you should use active record attribute method: saved_change_to_attribute?
saved_change_to_attribute?(attr_name, **options)`
Did this attribute change when we last saved? This method can be
invoked as saved_change_to_name? instead of
saved_change_to_attribute?("name"). Behaves similarly to
attribute_changed?. This method is useful in after callbacks to
determine if the call to save changed a certain attribute.
Options
from When passed, this method will return false unless the original
value is equal to the given option
to When passed, this method will return false unless the value was
changed to the given value
So your model will look like this, if you want to call some method based on the change in attribute value:
class Claim < ApplicationRecord
after_save :do_this, if: Proc.new { saved_change_to_status?(from: nil, to: 'pending') }
after_save :do_that, if: Proc.new { saved_change_to_status?(from: 'pending', to: 'approved') }
def do_this
..
..
end
def do_that
..
..
end
end
And if you don't want to check for value change in callback, you can do the following::
class Claim < ApplicationRecord
after_save: :do_this, if: saved_change_to_status?
def do_this
..
..
end
end
I recommend you have a look at one of the available state machine plugins:
acts_as_state_machine
alter_ego
Either one will let you setup states and transitions between states. Very useful and easy way of handling your requirements.
I've seen the question rise in many places, so I wrote a tiny rubygem for it, to make the code a little nicer (and avoid a million if/else statements everywhere): https://github.com/ronna-s/on_change.
I hope that helps.
You will be much better off using a well tested solution such as the state_machine gem.
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