MongoDB 中的查询选项

Python 中的 MongoDB 入门

Filip Schouwenaars

Machine Learning Researcher

限制结果数量

from pymongo import MongoClient
client = MongoClient()
mov = client.film.movies


# 获取所有电影（游标）
all_movies = mov.find()


# 有多少？
len(list(all_movies))

from pymongo import MongoClient
client = MongoClient()
mov = client.film.movies


# 获取 5 部电影（游标）
limit_movies = mov.find().limit(5)


# 有多少？
len(list(limit_movies))

升序与降序排序

# 按标题升序（A-Z）
t_sort = mov.find().sort("title", 1)
list(t_sort)

[
    {
        'title': '12 angry men',
        'release_year': 1957,
        ...
    },
    {
        'title': 'a beautiful mind',
        'release_year': 2001,
        ...
    },
    ...
]

# 按上映年份降序（高到低）
ry_sort = mov.find().sort("release_year", -1)
list(ry_sort)

[
    {
          'title': 'dune: part two',
        'release_year': 2024,
        ...
    },
     {
        'title': 'barbie',
        'release_year': 2023,
          ...
    },
    ...
]

统计匹配的文档数

from pymongo import MongoClient
client = MongoClient()
mov = client.film.movies


# 用 find() 统计动作片数量
len(list(mov.find({ "genre": "action" })))

# 更好的统计方式
mov.count_documents({ "genre": "action" })

用投影塑造结果集

movies = mov.find({}, {
  "title": 1, "rating": 1,
})
list(movies)

[
 {'_id': '6...f', 'rating': 7.6, 'title': 'superbad'},
 {'_id': '6...0', 'rating': 8.6, 'title': 'interstellar'},
 {'_id': '6...1', 'rating': 8.8, 'title': 'inception'},
 {'_id': '6...2', 'rating': 9.2, 'title': 'the godfather'},
 {'_id': '6...3', 'rating': 8,   'title': 'the revenant'},
 ...
]

movies = mov.find({}, {
  "title": 1, "rating": 1, "_id": 0
})
list(movies)

[
 {'title': 'superbad', 'rating': 7.6},
 {'title': 'interstellar', 'rating': 8.6},
 {'title': 'inception', 'rating': 8.8},
 {'title': 'the godfather', 'rating': 9.2},
 {'title': 'the revenant', 'rating': 8},
 ...
]

开始练习吧！

Python 中的 MongoDB 入门