Embeds_many child property not persisted when saving parent - ruby-on-rails

Question

I've been looking for some days without finding the exact answer to my problem which is as simple as that : I have a simple model, with books and authors. A book embeds many authors, and an author is embedded in book. But whenever I'm saving a new book, the author array is not persisted.
What I have is an angular 7 application, calling a ROR API. My Rails versions is 5.2.2. I am using mongoid 7.0 for persistence.
My API was generated with rails g scaffold, and with the --api and --skip-active-record flags.
I first had a problem with the mapping of my properties. My Angular APP sends JSON in lowerCamelCase, when Rails awaits form lower_snake_case vars. I managed to bypass this problem by adding a middleware (correct me if I'm wrong on this one) in my initializers which converts camelCase to snake_case.
# Transform JSON request param keys from JSON-conventional camelCase to
# Rails-conventional snake_case:
ActionDispatch::Request.parameter_parsers[:json] = -> (raw_post) {
# Modified from action_dispatch/http/parameters.rb
data = ActiveSupport::JSON.decode(raw_post)
data = {:_json => data} unless data.is_a?(Hash)
# Transform camelCase param keys to snake_case:
data.deep_transform_keys!(&:underscore)
}
From what I found looking for my problem, it could have been a problem with strong params, so I tried to get awat with this in my book_params
def book_params
#params.fetch(:book, {})
params.require(:book).permit(:title, :release_date, authors_attributes: [:name, :last_name, :birth_date])
end
These are my model :
class Person
include Mongoid::Document
field :last_name, type: String
field :first_name, type: String
field :birth_date, type: Date
end
class Author < Person
include Mongoid::Document
embedded_in :book
end
class Book
include Mongoid::Document
field :title, type: String
field :release_date, type: Date
embeds_many :authors
accepts_nested_attributes_for :authors
end
And this is POST in my book controller (generated with Rails)
# POST /books
def create
#book = Book.new(book_params)
if #book.save
render json: #book, status: :created, location: #book
else
render json: #book.errors, status: :unprocessable_entity
end
end
And here are exemple of a body sent, received and how it is processed by Rails :
Request sent by angular app
Request received and processed by Rails
We can see in the book object
"book"=>{"title"=>"azerty", "release_date"=>"2019-01-21T16:10:19.515Z"}}
That the authors have disappeared, though they were present in the request received by the server.
My question is then : what is the solution to this, or at least what am I missing ? Doesn't Mongoid automatically save children when using embedded documents and accepts_nested_attributes_for ? Should I manually save the children each time a parent is saved in my controller ?
Thanks in advance for helping me

Answer 1

You have to use nested attributes to save children records
Add following line in book model
accepts_nested_attributes_for :authors
And pass authors parameters in author_attributes, for exa:
{title: 'test', release_date: '', author_attributes: [{first_name: '', other_attributes of author}, {first_name: '', , other_attributes of author}]}
for more details please check Mongoid: Nested attributes
Pass perameters in this format
{"title"=>"test", "release_date"=>"2019-01-22", "book"=>{"title"=>"test", "release_date"=>"2019-01-22", "authors_attributes"=>[{"first_name"=>"test name", "last_name"=>"test", "birth_date"=>"2019-01-22T09:43:39.698Z"}]}}
Permit book params
def book_params
params.require(:book).premit(:first_name, :last_name, authors_attributes: %i[first_name last_name birth_date])
end