Multi keys index in MongoDB

multikeys_index_demo.js

// Prepare sample data on the Teachers collection
db.teachers.insert({'_id': 0, 'name': 'Maria'})
db.teachers.insert({'_id': 1, 'name': 'Jill'})
db.teachers.insert({'_id': 2, 'name': 'Anna'})
db.teachers.insert({'_id': 3, 'name': 'Lara'})

// Prepare sample data on the Students collection
db.students.insert({'_id':0, 'name':'Lisa', 'teachers': [0,1]})
db.students.insert({'_id':1, 'name':'Paulene', 'teachers': [0,1,3]})
db.students.insert({'_id':2, 'name':'Joey', 'teachers': [1,2,3]})
db.students.insert({'_id':3, 'name':'Sarah', 'teachers': [0,3]})

// Setup multi key index on the students-teachers property
db.students.ensureIndex({'teachers':1})

// Query students that are the pupils of both Lisa & Paulene
db.students.find({'teachers':{$all: [0,1]}})

// To see the statistic of the prior query, add explain after the find command
db.students.find({'teachers':{$all: [0,1]}}).explain()