NestedAttributeReassignable

Normal accepts_nested_attributes_for works find when all objects being created are unpersisted. But if the base object is unpersisted and being associated to pre-existing records, it will blow up:

pet = Pet.create!(name: 'Spot')
Person.create(name: 'Joe', pets_attributes: [{ id: pet.id }])
# => ActiveRecord::RecordNotFound: Couldn't find Pet with ID=1 for Person with ID=

This gem allows you to assign pre-existing records without error

Installation

Add this line to your application's Gemfile:

gem 'nested_attribute_reassignable'

And then execute:

$ bundle

Or install it yourself as:

$ gem install nested_attribute_reassignable

Usage

Instead of accepts_nested_attributes_for use reassignable_nested_attributes_for.
You can pass nested IDs or nested attributes, not both. If you pass both, the attributes will be dropped and the nested record will not update:

pet = Pet.create!(name: 'Spot')
person = Person.create(name: 'Joe', pets_attributes: [{ id: pet.id,
name: 'Elmo' }])
person.reload.pets.first.id == pet.id # => true
person.reload.pets.first.name # => 'Spot', not 'Elmo'

nested_attribute_reassignable internally calls accepts_nested_attributes_for with allow_destroy: true option.

Supports customizing the lookup_key for nested attributes as shown below

class Person < ApplicationRecord
  has_many    :pets
  has_many    :bills
  has_many    :services, through: :bills, through: :destroy

  reassignable_nested_attributes_for :services, lookup_key: :name
  reassignable_nested_attributes_for :pets, lookup_key: :name
end

rent    = Service.create!(name: 'Rent')
mobile  = Service.create!(name: 'Mobile')
cat     = Pet.create!(name: 'Cat')

person = Person.create({
  name: 'Joe',
  services_attributes: [{ id: rent.name }]),
  pets_attributes: [{ id: cat.name }])
}

person.reload.bills.first.service_id == rent.id # => true
person.reload.pets.first.id == cat.id # => true

person.update_attributes({
  pets_attributes: [{ id: cat.name, _destroy: true }])
}

#has_many 
person.reload.pets #=> []
Pet.all #=> [] deletes associated records

#has_many => through
person.update_attributes({
  services_attributes: [{ id: rent.name, _destroy: true }])
}

person.reload.bills #=> []
Service.all #=> [rent, mobile] won't destroy Service, only the join record

person.update_attributes({
  services_attributes: [{ id: rent.name, _delete: true }])
}

person.reload.bills #=> []
Service.all #=> [rent, mobile] won't delete Service, only the join record

_delete

Normal accepts_nested_attributes_for accepts a _destroy parameter for destroying the association. This will destroy the underlying record. If you only want to disassociate the record, you can now use _delete.

nonexistent_id

If an id or lookup_key is passed, and a record with this identifier does not exist, this library will raise an error by default.

You may not want this behavior, for instance if your API is accepting client-generated IDs on POSTs to create. In this scenario:

belongs_to :thing, nonexistent_id: :create

Instead of raising, this will create a record with the given ID.

Running the tests

This library uses appraisal to test against activerecord >= 4.1. Run

$ bin/appraisal activerecord-4 rspec
$ bin/appraisal activerecord-5 rspec