Extend custom Rails preloader with includes - ruby-on-rails

I'd like to trigger eager loading on a relation with an #includes call, that was modified with a custom preloader using ActiveRecord::Associations::Preloader on a Rails 7 app, Ruby 3.2:
class Product < ApplicationRecord
belongs_to :vendor
has_many :taxons
end
class Vendor < ApplicationRecord
has_many :products
end
records = Product.where(id: [1,2,3,4])
scope = Vendor.where.not(id: [5,6])
preloader = ActiveRecord::Associations::Preloader.new(records:, associations: :vendor, scope:).tap(&:call)
puts records.first.association_cached?(:vendor)
=> true
puts records.includes(:taxons).first.association_cached?(:vendor)
=> false
I need the scope: argument because some users aren't allowed to access certain resources.
Without the includes(:taxons) call, the association :vendor is correctly eager loaded and cached. But in the second case, it seems like the whole eager loading of Preloader is somehow dropped.
Is there a way to include a custom preloader as a chain argument along with other includes? I get an error when I try to include the preloader itself like this:
records.includes(preloader).to_a
ActiveRecord::AssociationNotFoundError: Association named '#<ActiveRecord::Associations::Preloader:0x00007f573bc31ab0>' was not found on Product; perhaps you misspelled it?
from /usr/local/bundle/gems/activerecord-7.0.4.2/lib/active_record/associations.rb:302:in `association'

What's happening here is that ActiveRecord::Associations::Preloader needs the objects to be initialized to fill in the data however calling any queries on ActiveRecord::Relation will reload the objects.
You have to call the Preloader after calling any reload causing method of ActiveRecord::Relation on records. It shouldn't have any performance difference from adding the custom preloader to the chain since it still would have to be called each time at the end.
Adding it to the chain would require some monkey patching. The starting point for it would be ActiveRecord:: Relation#preload_associations to where you have to pass the scope.
If you just need the data, call includes first, then Preloader. I you need the data first without taxons and later include them, call a second custom preloader to load the taxons data. It will also have a positive impact on speed since products and vendors don't have to be loaded and initialized again.
records = Product.where(id: [1,2,3,4])
scope = Vendor.where.not(id: [5,6])
ActiveRecord::Associations::Preloader.new(records:, associations: :vendor, scope:).tap(&:call)
# associations filtered by the scope are initialized but return nil, although association_id is present
records.map{|r| r.association_cached?(:vendor)}
=> [true, true, true, true]
records.map{|r| r.association_cached?(:taxons)}
=> [false, false, false, false]
ActiveRecord::Associations::Preloader.new(records:, associations: :taxons).tap(&:call)
records.map{|r| r.association_cached?(:vendor)}
=> [true, true, true, true]
records.map{|r| r.association_cached?(:taxons)}
=> [true, true, true, true]

As Jan Vítek pointed out, any queries called on a relation will reload all objects, and therefore loose all already eager loaded associations.
Due to the structure of the code, I can't guarantee to always call the custom ActiveRecord::Associations::Preloader, so I came up with a little monkey patch for ActiveRecord::Relation#preload_associations:
raise "ActiveRecord::Relation#preload_associations is no longer available, check patch!" unless ActiveRecord::Relation.method_defined? :preload_associations
raise "ActiveRecord::Relation#preload_associations arity != 1, check patch!" unless ActiveRecord::Relation.instance_method(:preload_associations).arity == 1
module PreloadWithScopePatch
def preload_with_scope(association, scope)
scope = model.reflect_on_association(association).klass.where(scope) if scope.is_a?(Hash)
(#preload_with_scope ||= []).push([association, scope])
self
end
def preload_associations(records)
super.tap do
Array(#preload_with_scope).each do |associations, scope|
ActiveRecord::Associations::Preloader.new(records:, associations:, scope:).call
end
end
end
end
ActiveRecord::Relation.prepend(PreloadWithScopePatch)
ActiveRecord::Base.singleton_class.delegate(:preload_with_scope, to: :all)
Now you can use it like this:
records = Product.where(id: [1,2,3,4]).preload_with_scope(:vendor, Vendor.where.not(id: [5,6])).includes(:taxons)
records.map { |r| r.association_cached?(:vendor) }
=> [true, true, true, true]
records.map { |r| r.association_cached?(:taxons) }
=> [true, true, true, true]

Related

How to add condition for all where query for an ActiveRecordModel?

I have a user table in my rails application and the application uses many where conditions for this model throughout the application in many controller methods.
Now i have to add an extra attribute for the where condition.
is there a way to do the following and how? instead of adding the extra attribute to all the where condition used in the entire application can i write a custom where to the user model so the condition will be pre-added to the where in entire application for the user model.
i found out the source for the where
def where(opts = :chain, *rest)
if :chain == opts
WhereChain.new(spawn)
elsif opts.blank?
self
else
spawn.where!(opts, *rest)
end
end
my where condition in the controller methods now:
User.where(:status => true, :country => "IN")
this condition and similar conditions are used in many methods in application and i want to get the user who has not :deactivated.
i can make changes to all where condition like
User.where(:status => true, :country => "IN", :deactivated => false)
instead i thought of writing a custom where that precheck :deactivated => false
Default Scope:
class User < ActiveRecord::Base
default_scope -> { where(deactivated: false) }
end
You can use default_scope.
Now, whenever you query User, automatically the default scope query will get appended.
For more details on default_scope, please refer:
https://api.rubyonrails.org/classes/ActiveRecord/Scoping/Default/ClassMethods.html#method-i-default_scope
If there are usecases that prevent you from using default_scope, then you can use custom scopes or unscope the default scope.
Unscoping:
You can unscope in Project model if you want to remove the default scope.
belongs_to :user, ->{ unscope(where: :deactivated) }
Or you can fetch all user and then unscope
project.users.unscoped
Custom Scope:
class User < ActiveRecord::Base
scope :deactivated, ->(deactivated = false) { where(deactivated: deactivated) }
end
Now, to make use of that scope, you can query like this:
User.deactivated.where(:status => true, :country => "IN")
For reference:
https://api.rubyonrails.org/classes/ActiveRecord/Scoping/Named/ClassMethods.html#method-i-scope

model association with a scope for trashable module

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.

Rails Active Record Nested Attributes Validation which are in the same request

I have two models house and booking.Everything is okey over booking_date validation. But when I try to update or create multi booking in the same request. Validation can't check the invalid booking in the same request params.
Let give an example assume that booking table is empty.
params = { :house => {
:title => 'joe', :booking_attributes => [
{ :start_date => '2012-01-01', :finish_date => '2012-01-30 },
{ :start_date => '2012-01-15', :finish_date => '2012-02-15 }
]
}}
Second booking also save but its start_date is between first booking interval. When I save them one by one validation works.
class House < ActiveRecord::Base
attr_accessible :title, :booking_attributes
has_many :booking
accepts_nested_attributes_for :booking, reject_if: :all_blank, allow_destroy: true
end
class Booking < ActiveRecord::Base
belongs_to :house
attr_accessible :start_date, :finish_date
validate :booking_date
def booking_date
# Validate start_date
if Booking.where('start_date <= ? AND finish_date >= ? AND house_id = ?',
self.start_date, self.start_date, self.house_id).exists?
errors.add(:start_date, 'There is an other booking for this interval')
end
# Validate finish_date
if Booking.where('start_date <= ? AND finish_date >= ? AND house_id = ?',
self.finish_date, self.finish_date, self.house_id).exists?
errors.add(:finish_date, 'There is an other booking for this interval')
end
end
end
I google nearly 2 hours and could not find anything. What is the best approach to solve this problem?
Some resources
http://api.rubyonrails.org/classes/ActiveRecord/NestedAttributes/ClassMethods.html
http://railscasts.com/episodes/196-nested-model-form-part-1
This was only a quick 15-minutes research on my part, so I may be wrong, but I believe here's the root cause of your problem:
What accepts_nested_attributes_for does under the hood, it calls 'build' for new Booking objects (nothing is validated at this point, objects are created in memory, not stored to db) and registers validation and save hooks to be called when the parent object (House) is saved. So, in my understanding, all validations are first called for all created objects (by calling 'valid?' for each of them. Then, again if I get it right, they are saved using insert_record(record,false) which leads to save(:validate => false), so validations are not called for the 2nd time.
You can look at the sources inside these pages: http://apidock.com/rails/v3.2.8/ActiveRecord/AutosaveAssociation/save_collection_association,
http://apidock.com/rails/ActiveRecord/Associations/HasAndBelongsToManyAssociation/insert_record
You validations call Booking.where(...) to find the overlapping dates-ranges. At this point the newly created Booking objects are still only in memory, not saved to the db (remember, we are just calling valid? for each of them in the loop, saves will be done later). Thus Booking.where(...) which runs a query against a DB doesn't find them there and returns nothing. Thus they all pass valid? stage and then saved.
In a nutshell, the records created together in such a way will not be cross-validated against each other (only against the previously existing records in the database). Hence the problem you see.
Thus either save them one-by-one, or check for such date-overlapping cases among the simultaneously created Bookings yourself before saving.

Rails counter_cache not updating correctly

Using Rails 3.1.3 and I'm trying to figure out why our counter caches aren't being updated correctly when changing the parent record id via update_attributes.
class ExhibitorRegistration < ActiveRecord::Base
belongs_to :event, :counter_cache => true
end
class Event < ActiveRecord::Base
has_many :exhibitor_registrations, :dependent => :destroy
end
describe ExhibitorRegistration do
it 'correctly maintains the counter cache on events' do
event = Factory(:event)
other_event = Factory(:event)
registration = Factory(:exhibitor_registration, :event => event)
event.reload
event.exhibitor_registrations_count.should == 1
registration.update_attributes(:event_id => other_event.id)
event.reload
event.exhibitor_registrations_count.should == 0
other_event.reload
other_event.exhibitor_registrations_count.should == 1
end
end
This spec fails indicating that the counter cache on event is not being decremented.
1) ExhibitorRegistration correctly maintains the counter cache on events
Failure/Error: event.exhibitor_registrations_count.should == 0
expected: 0
got: 1 (using ==)
Should I even expect this to work or do I need to manually track the changes and update the counter myself?
From the fine manual:
:counter_cache
Caches the number of belonging objects on the associate class through the use of increment_counter and decrement_counter. The counter cache is incremented when an object of this class is created and decremented when it’s destroyed.
There's no mention of updating the cache when an object is moved from one owner to another. Of course, the Rails documentation is often incomplete so we'll have to look at the source for confirmation. When you say :counter_cache => true, you trigger a call to the private add_counter_cache_callbacks method and add_counter_cache_callbacks does this:
Adds an after_create callback which calls increment_counter.
Adds an before_destroy callback which calls decrement_counter.
Calls attr_readonly to make the counter column readonly.
I don't think you're expecting too much, you're just expecting ActiveRecord to be more complete than it is.
All is not lost though, you can fill in the missing pieces yourself without too much effort. If you want to allow reparenting and have your counters updated, you can add a before_save callback to your ExhibitorRegistration that adjusts the counters itself, something like this (untested demo code):
class ExhibitorRegistration < ActiveRecord::Base
belongs_to :event, :counter_cache => true
before_save :fix_counter_cache, :if => ->(er) { !er.new_record? && er.event_id_changed? }
private
def fix_counter_cache
Event.decrement_counter(:exhibitor_registration_count, self.event_id_was)
Event.increment_counter(:exhibitor_registration_count, self.event_id)
end
end
If you were adventurous, you could patch something like that into ActiveRecord::Associations::Builder#add_counter_cache_callbacks and submit a patch. The behavior you're expecting is reasonable and I think it would make sense for ActiveRecord to support it.
If your counter has been corrupted or you've modified it directly by SQL, you can fix it.
Using:
ModelName.reset_counters(id_of_the_object_having_corrupted_count, one_or_many_counters)
Example 1: Re-compute the cached count on the post with id = 17.
Post.reset_counters(17, :comments)
Source
Example 2: Re-compute the cached count on all your articles.
Article.ids.each { |id| Article.reset_counters(id, :comments) }
I recently came across this same problem (Rails 3.2.3). Looks like it has yet to be fixed, so I had to go ahead and make a fix. Below is how I amended ActiveRecord::Base and utilize after_update callback to keep my counter_caches in sync.
Extend ActiveRecord::Base
Create a new file lib/fix_counters_update.rb with the following:
module FixUpdateCounters
def fix_updated_counters
self.changes.each {|key, value|
# key should match /master_files_id/ or /bibls_id/
# value should be an array ['old value', 'new value']
if key =~ /_id/
changed_class = key.sub(/_id/, '')
changed_class.camelcase.constantize.decrement_counter(:"#{self.class.name.underscore.pluralize}_count", value[0]) unless value[0] == nil
changed_class.camelcase.constantize.increment_counter(:"#{self.class.name.underscore.pluralize}_count", value[1]) unless value[1] == nil
end
}
end
end
ActiveRecord::Base.send(:include, FixUpdateCounters)
The above code uses the ActiveModel::Dirty method changes which returns a hash containing the attribute changed and an array of both the old value and new value. By testing the attribute to see if it is a relationship (i.e. ends with /_id/), you can conditionally determine whether decrement_counter and/or increment_counter need be run. It is essnetial to test for the presence of nil in the array, otherwise errors will result.
Add to Initializers
Create a new file config/initializers/active_record_extensions.rb with the following:
require 'fix_update_counters'
Add to models
For each model you want the counter caches updated add the callback:
class Comment < ActiveRecord::Base
after_update :fix_updated_counters
....
end
A fix for this has been merged in to active record master
https://github.com/rails/rails/issues/9722
The counter_cache function is designed to work through the association name, not the underlying id column. In your test, instead of:
registration.update_attributes(:event_id => other_event.id)
try
registration.update_attributes(:event => other_event)
More information can be found here: http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html

Rails: How can I set default values in ActiveRecord?

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

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