Finding documents

Introduction to MongoDB in Python

Donny Winston

Instructor

An example "laureates" document

{'_id': ObjectId('5b9ac94ff35b63cf5231ccb1'),
 'born': '1845-03-27',
 'bornCity': 'Lennep (now Remscheid)',
 'bornCountry': 'Prussia (now Germany)',
 'bornCountryCode': 'DE',
 'died': '1923-02-10',
 'diedCity': 'Munich',
 'diedCountry': 'Germany',
 'diedCountryCode': 'DE',
 'firstname': 'Wilhelm Conrad',
 'gender': 'male',
 'id': '1',
 'prizes': [{'affiliations': [{'city': 'Munich',
                               'country': 'Germany',
                               'name': 'Munich University'}],
             'category': 'physics',
             'motivation': '"in recognition of the extraordinary services '
                           'he has rendered by the discovery of the '
                           'remarkable rays subsequently named after him"',
             'share': '1',
             'year': '1901'}],
 'surname': 'Röntgen'}

Filters as (sub)documents

Count documents by providing a filter document to match.

filter_doc = {
 'born': '1845-03-27',
 'diedCountry': 'Germany',
 'gender': 'male',
 'surname': 'Röntgen'
}

db.laureates.count_documents(filter_doc)

Simple filters

db.laureates.count_documents({'gender': 'female'})

db.laureates.count_documents({'diedCountry': 'France'})

db.laureates.count_documents({'bornCity': 'Warsaw'})

Composing filters

filter_doc = {'gender': 'female',
              'diedCountry': 'France',
              'bornCity': 'Warsaw'}
db.laureates.count_documents(filter_doc)

db.laureates.find_one(filter_doc)

{'_id': ObjectId('5bc56154f35b634065ba1be9'),
 'born': '1867-11-07',
 'bornCity': 'Warsaw',
 'bornCountry': 'Russian Empire (now Poland)',
 'bornCountryCode': 'PL',
 'died': '1934-07-04',
 'diedCity': 'Sallanches',
 'diedCountry': 'France',
 'diedCountryCode': 'FR',
 'firstname': 'Marie',
 ...

Query operators

Value in a range $in: <list>

db.laureates.count_documents({
 'diedCountry': {
  '$in': ['France', 'USA']}})

Not equal $ne : <value>

db.laureates.count_documents({
 'diedCountry': {
  '$ne': 'France'}})

Query syntax:

{  
  # Match a single value exactly:
  'field_name1': value1,

  # Use operators:  
  'field_name2': {
      $operator1: value1,
      $operator2: value2,
      ... # more operators
    },
    ... # more fields
}

Query operators

Comparison:
- > :$gt, ≥ : $gte
- < :$lt, ≤ : $lte

db.laureates.count_documents({
 'diedCountry': {
  '$gt': 'Belgium',
  '$lte': 'USA'}})

(Strings are compared lexicographically)

Query syntax:

{  
  # Match a single value exactly:
  'field_name1': value1,

  # Use operators:  
  'field_name2': {
      $operator1: value1,
      $operator2: value2,
      ... # more operators
    },
    ... # more fields
}

Let's Practice!

Introduction to MongoDB in Python