Mongoid和Mongodb查询

Question

I have a data strcuture like this

Courses
{
    "name" : "Course1",
    "student_id"
    "subjects" :
    [{
      "level" : "1",
      "short_name" : "Maths",
      "topics" : [{
              "name" : "Algebra 101",
              "week" : "1",
              "submission_week" : ISODate("2013-07-28T00:00:00Z"),
              "correction_week" : ISODate("2013-07-28T00:00:00Z")
              },
              {
              "name" : "Algebra 201",
              "week" : "1",
              "submission_week" : ISODate("2013-07-28T00:00:00Z"),
              "correction_week" : ISODate("2013-07-28T00:00:00Z")
              }
     ]},
     {
      "level" : "2",
      "short_name" : "Chem"
     }
    ]
}

Using Mongoid I am trying to retrieve all topics.

I have tried all sorts of queries but cannot seem get it.

eg I don't understand why this doesn't work?

Topic.where( name: "Algebra 101", 'subject.short_name' =>"Maths", 'subject.course.name' =>"Course1")

Can I query like this?

My ruby code is

class Course
  embeds_many :subjects

class Subject
  embedded_in :course
  embeds_many :topics

class Topic
  embedded_in :subject

Answer 1

A far as I know it's only possible to make such a query on the top-most model (in this case Course ); I have not seen a way to directly obtain an embedded model like that yet.

So this should work, but only gives you the Course :

Course.where(name: 'Course1', 'subjects.short_name' => 'Maths', 'subjects.topics.name' => "Algebra 101")

And this is the (unfortunately rather ugly) query that should give you what you want:

Course.where(name: 'Course1').subjects.where(short_name: 'Maths').topics.where(name: 'Algebra 101')