Mongoid Search by Array of Association Id's

Question

I have a Rails 4.2, Mongoid 4 project with these models:

class Customer #aka Company
  include Mongoid::Document

  has_many :branches
end

class Branch
  include Mongoid::Document  

  field :name, type: String, default: ""

  belongs_to :customer
end

I want to find all the Customers (aka Companies) that have a branch with name "New York". I would think that this code would work:

branches = Branch.where(name: "New York").map(&:_id)
=> [BSON::ObjectId('54f76cef6272790316390100')]
Customer.where(:branch_ids => branches).entries

However, it always returns an empty array, no matter what I try. In place of branch_ids, I've also tried branches, branch, branches_id, and others, but to no avail. I've also tried to convert the BSON::ObjectID to plain string, but that doesn't work either.

So, basically, how can I search a model based on an array of association ids? Thanks.

Answer 1

If the relations are

Customer has_many :branches and

Branch belongs_to :customer,

Then branches collection will have a customer_id column and not the reverse. So you can do

cust_ids = Branch.where(name: "New York").map(&:customer_id)
Customer.find(cust_ids)

Since you need only the customer ids from the first query, it is advisable to use pluck

cust_ids = Branch.where(name: "New York").pluck(:customer_id)