Rails Mongoid : Query embedded document and access to Mongoid criteria - ruby-on-rails

Question

I have an application where users can create many travels, and they can invite their facebook friends. In the travel document, there is a field "participants" that is an embedded document, Participant model embedded in Travel model.
Here are my models :
class Travel
include Mongoid::Document
include Mongoid::Timestamps
# relations
belongs_to :user
# fields
field :title, type: String
field :description, type: String
field :begin_date, type: Date
field :end_date, type: Date
field :budget, type: Integer
field :go_back, type: Boolean
field :title_namespace, type: String
# friends
embeds_many :participants
accepts_nested_attributes_for :participants
end
class Participant
include Mongoid::Document
include Mongoid::Timestamps
field :name, type: String
field :user_id, type: String
# relations
embedded_in :travel, :inverse_of => :participants
end
When I try to display travel where users have been invited, with this request :
#travel_participations = Travel.where('participants.user_id' => #user.id)
I don't have any result, even if I have this line in byebug :
#<Mongoid::Criteria
selector: {"participants.user_id"=>BSON::ObjectId('592c8da58511989ec850921e')}
options: {}
class: Travel
embedded: false>
So when I put this on my view :
<% unless #participations.nil? %>
<% #travel_participations.each do |travel_participation| %>
<p> <%= travel_participation.title %> </p>
<% end %>
<% end %>
I tried with .all, .first, .to_a, .as_json, no results ... Some one know where is the problem ?

Answer 1

You have this in your embedded model:
field :user_id, type: String
but your query is using a BSON::ObjectId:
Travel.where('participants.user_id' => #user.id)
as shown in the raw query:
selector: {"participants.user_id"=>BSON::ObjectId('592c8da58511989ec850921e')}
Your embedded document probably has a string field like:
"user_id": "592c8da58511989ec850921e"
rather than the ObjectId you're looking for:
"user_id": ObjectId("592c8da58511989ec850921e")
so you won't find what you're looking for due to the type mismatch.
Either fix the embedded field's type:
field :user_id, type: BSON::ObjectId
or query it as the string it is:
Travel.where('participants.user_id' => #user.id.to_s)
Changing the type will involve fix up whatever data you already have, changing the query is ugly in a different way.
Sometimes Mongoid will convert between strings and ObjectIds for you, sometimes it won't. When I used Mongoid I patched to_bson_id methods into BSON::ObjectId, String, Mongoid::Document, ... so that I could say things like:
Model.where(:some_id => some_id.to_bson_id)
and not have to constantly worry about what type some_id was. I also made sure that all ID fields were always specified as BSON::ObjectId.