5.1 E-commerce queries

5.1.1 Products, categories and reviews

  1. product = db.products.findOne({'slug': 'wheel-barrow-9092'})
  2. db.categories.findOne({'_id': product['main_cat_id']})
  3. db.reviews.find({'product_id': product['_id']})

find returns a cursor object, whereas findOnereturns a document
a cursor is returned even when you apply a limit:

  1. db.products.find({'slug': 'wheel-barrow-9092'}).limit(1)

sikp, limit, and sort query options

paginate the review document:

  1. db.reviews.find({'product_id': product['_id']}).skip(0).limit(12)
  1. db.reviews.find({'product_id': product['_id']})
  2.   .sort({'helpful_votes': -1})
  3.   .limit(12)
  1.   page_number = 1
  2.   product = db.products.findOne({'slug': 'wheel-barrow-9092'})
  3.   category = db.categories.findOne({'_id': product['main_cat_id']})
  4.   reviews_count = db.reviews.count({'product_id': product['_id']})
  5.   reviews = db.reviews.find({'product_id': product['_id']}).
  6.     skip((page_number - 1) * 12).
  7.     limit(12).
  8.     sort({'helpful_votes': -1})

Product listing page

  1.   page_number = 1
  2.   category = db.categories.findOne({'slug': 'gardening-tools'})
  3.   siblings = db.categories.find({'parent_id': category['_id']})
  4.   products = db.products.find({'category_id': category['_id']})
  5.     .skip((page_number - 1) * 12)
  6.     .limit(12)
  7.     .sort({'helpful_votes': -1})

get thes root-level categories

  1. categories = db.categories.find({'parent_id':null})

5.1.2 Users and orders

search user by username and password:

  1. db.users.findOne({
  2.   'username': 'kbanker',
  3.   'hashed_password': 'bd1cfa194c3a603e7186780824b04419'})

you can limit the fields returned using a projection:

  1. db.users.findOne({
  2.   'username': 'kbanker',
  3.   'hashed_password': 'bd1cfa194c3a603e7186780824b04419'},
  4.   {'_id': 1})

the response now consists exclusively of the document’s _id field:
image.png

Partial match queries in users

  1. db.users.find({'last_name': 'Banker'})

suppose you know that the user’s last name starts with Ba

  1. db.users.find({'last_name': /^Ba/})

Querying specify ranges

  1. db.users.find({'addresses.zip': {'$gt': 10019, '$lt': 10040}})

5.2 MongoDB’s query language

suggestion:
skim this section and revisit it when you need to writ more advanced queries for your application