Python 与 MongoDB⚓︎

Python 是一种后端技术，可以连接不同的数据库应用。它可以连接 SQL 和 NoSQL 数据库。本节我们把 Python 连接到 NoSQL 数据库 MongoDB。

MongoDB⚓︎

MongoDB 是一种 NoSQL 数据库。MongoDB 以类似 JSON 的文档形式存储数据，因此非常灵活且易于扩展。让我们看看 SQL 与 NoSQL 数据库的不同术语。下表展示了 SQL 与 NoSQL 数据库的区别。

SQL 与 NoSQL⚓︎

本节我们将聚焦 NoSQL 数据库 MongoDB。请到 mongoDB 注册：点击 Sign in，然后在下一页点击 Register。

填写字段并点击 Continue。

选择免费计划。

选择就近的免费区域，并为集群起一个名字。

现在已创建免费沙箱环境。

允许所有本地主机访问。

添加用户和密码。

创建 MongoDB URI 链接。

选择 Python 3.6 或更高版本的驱动。

获取连接字符串（MongoDB URI）⚓︎

复制连接字符串链接，你会得到类似这样的内容：

mongodb+srv://asabeneh:<password>@30daysofpython-twxkr.mongodb.net/test?retryWrites=true&w=majority

不必担心这个 URL，它只是用来把应用连接到 MongoDB 的手段。把密码占位符替换为你添加用户时使用的密码。

示例：

mongodb+srv://asabeneh:123123123@30daysofpython-twxkr.mongodb.net/test?retryWrites=true&w=majority

现在我已全部替换完成，密码是 123123，数据库名是 thirty_days_python。这只是示例，你的密码必须比示例密码更强。

Python 需要 MongoDB 驱动才能访问 MongoDB 数据库。我们将使用 pymongo 和 dnspython 把应用连接到 MongoDB。在项目目录中安装 pymongo 和 dnspython。

pip install pymongo dnspython

要使用 mongodb+srv:// URI，必须安装 "dnspython" 模块。dnspython 是 Python 的 DNS 工具包，支持几乎所有记录类型。

将 Flask 应用连接到 MongoDB 集群⚓︎

# let's import the flask
from flask import Flask, render_template
import os # importing operating system module
MONGODB_URI = 'mongodb+srv://asabeneh:your_password_goes_here@30daysofpython-twxkr.mongodb.net/test?retryWrites=true&w=majority'
client = pymongo.MongoClient(MONGODB_URI)
print(client.list_database_names())

app = Flask(__name__)
if __name__ == '__main__':
    # for deployment we use the environ
    # to make it work for both production and development
    port = int(os.environ.get("PORT", 5000))
    app.run(debug=True, host='0.0.0.0', port=port)

运行上面的代码时，我们会得到默认的 MongoDB 数据库。

['admin', 'local']

创建数据库和集合⚓︎

让我们创建一个数据库；在 MongoDB 中，若数据库和集合不存在，会在使用时创建。我们创建一个名为 thirty_days_of_python 的数据库和 students 集合。

创建数据库：

db = client.name_of_databse # we can create a database like this or the second way
db = client['name_of_database']

# let's import the flask
from flask import Flask, render_template
import os # importing operating system module
MONGODB_URI = 'mongodb+srv://asabeneh:your_password_goes_here@30daysofpython-twxkr.mongodb.net/test?retryWrites=true&w=majority'
client = pymongo.MongoClient(MONGODB_URI)
# Creating database
db = client.thirty_days_of_python
# Creating students collection and inserting a document
db.students.insert_one({'name': 'Asabeneh', 'country': 'Finland', 'city': 'Helsinki', 'age': 250})
print(client.list_database_names())

app = Flask(__name__)
if __name__ == '__main__':
    # for deployment we use the environ
    # to make it work for both production and development
    port = int(os.environ.get("PORT", 5000))
    app.run(debug=True, host='0.0.0.0', port=port)

创建数据库后，我们还创建了 students 集合，并用 insert_one() 方法插入了一条文档。现在，数据库 thirty_days_of_python 和 students 集合已创建，文档也已插入。检查你的 MongoDB 集群，你会同时看到数据库和集合。集合内部会有一条文档。

['thirty_days_of_python', 'admin', 'local']

如果在 MongoDB 集群上看到这些，说明你已成功创建了数据库和集合。

从图中可以看到，文档创建时带有一个很长的 id，它充当主键。每次我们创建文档时，MongoDB 都会为它创建唯一 id。

向集合插入多条文档⚓︎

insert_one() 方法一次插入一条；若想一次插入多条文档，可用 insert_many() 方法或 for 循环。我们可以用 for 循环一次插入多条文档。

# let's import the flask
from flask import Flask, render_template
import os # importing operating system module
MONGODB_URI = 'mongodb+srv://asabeneh:your_password_goes_here@30daysofpython-twxkr.mongodb.net/test?retryWrites=true&w=majority'
client = pymongo.MongoClient(MONGODB_URI)

students = [
        {'name':'David','country':'UK','city':'London','age':34},
        {'name':'John','country':'Sweden','city':'Stockholm','age':28},
        {'name':'Sami','country':'Finland','city':'Helsinki','age':25},
    ]
for student in students:
    db.students.insert_one(student)


app = Flask(__name__)
if __name__ == '__main__':
    # for deployment we use the environ
    # to make it work for both production and development
    port = int(os.environ.get("PORT", 5000))
    app.run(debug=True, host='0.0.0.0', port=port)

MongoDB Find⚓︎

find() 和 findOne() 是在 MongoDB 数据库集合中查找数据的常用方法，类似于 MySQL 中的 SELECT 语句。让我们用 find_one() 方法获取集合中的一条文档。

*find_one({"_id": ObjectId("id"}): 若未提供 id，则获取第一条匹配项

# let's import the flask
from flask import Flask, render_template
import os # importing operating system module
MONGODB_URI = 'mongodb+srv://asabeneh:your_password_goes_here@30daysofpython-twxkr.mongodb.net/test?retryWrites=true&w=majority'
client = pymongo.MongoClient(MONGODB_URI)
db = client['thirty_days_of_python'] # accessing the database
student = db.students.find_one()
print(student)


app = Flask(__name__)
if __name__ == '__main__':
    # for deployment we use the environ
    # to make it work for both production and development
    port = int(os.environ.get("PORT", 5000))
    app.run(debug=True, host='0.0.0.0', port=port)

{'_id': ObjectId('5df68a21f106fe2d315bbc8b'), 'name': 'Asabeneh', 'country': 'Helsinki', 'city': 'Helsinki', 'age': 250}

上面的查询返回第一条记录，但我们可以用特定的 _id 定位具体文档。我们用 David 的 id 获取 David 对象。 '_id':ObjectId('5df68a23f106fe2d315bbc8c')

# let's import the flask
from flask import Flask, render_template
import os # importing operating system module
from bson.objectid import ObjectId # id object
MONGODB_URI = 'mongodb+srv://asabeneh:your_password_goes_here@30daysofpython-twxkr.mongodb.net/test?retryWrites=true&w=majority'
client = pymongo.MongoClient(MONGODB_URI)
db = client['thirty_days_of_python'] # accessing the database
student = db.students.find_one({'_id':ObjectId('5df68a23f106fe2d315bbc8c')})
print(student)

app = Flask(__name__)
if __name__ == '__main__':
    # for deployment we use the environ
    # to make it work for both production and development
    port = int(os.environ.get("PORT", 5000))
    app.run(debug=True, host='0.0.0.0', port=port)

{'_id': ObjectId('5df68a23f106fe2d315bbc8c'), 'name': 'David', 'country': 'UK', 'city': 'London', 'age': 34}

通过上面的示例，我们学会了如何使用 find_one()。接下来看 find()。

find(): 若不传入查询对象，则返回集合中的所有结果。该对象是 pymongo.cursor 对象。

# let's import the flask
from flask import Flask, render_template
import os # importing operating system module

MONGODB_URI = 'mongodb+srv://asabeneh:your_password_goes_here@30daysofpython-twxkr.mongodb.net/test?retryWrites=true&w=majority'
client = pymongo.MongoClient(MONGODB_URI)
db = client['thirty_days_of_python'] # accessing the database
students = db.students.find()
for student in students:
    print(student)

app = Flask(__name__)
if __name__ == '__main__':
    # for deployment we use the environ
    # to make it work for both production and development
    port = int(os.environ.get("PORT", 5000))
    app.run(debug=True, host='0.0.0.0', port=port)

{'_id': ObjectId('5df68a21f106fe2d315bbc8b'), 'name': 'Asabeneh', 'country': 'Finland', 'city': 'Helsinki', 'age': 250}
{'_id': ObjectId('5df68a23f106fe2d315bbc8c'), 'name': 'David', 'country': 'UK', 'city': 'London', 'age': 34}
{'_id': ObjectId('5df68a23f106fe2d315bbc8d'), 'name': 'John', 'country': 'Sweden', 'city': 'Stockholm', 'age': 28}
{'_id': ObjectId('5df68a23f106fe2d315bbc8e'), 'name': 'Sami', 'country': 'Finland', 'city': 'Helsinki', 'age': 25}

我们可以通过在 find({}, {}) 中传入第二个对象来指定返回哪些字段。0 表示不包含，1 表示包含，但不能混用 0 和 1，_id 除外。

# let's import the flask
from flask import Flask, render_template
import os # importing operating system module

MONGODB_URI = 'mongodb+srv://asabeneh:your_password_goes_here@30daysofpython-twxkr.mongodb.net/test?retryWrites=true&w=majority'
client = pymongo.MongoClient(MONGODB_URI)
db = client['thirty_days_of_python'] # accessing the database
students = db.students.find({}, {"_id":0,  "name": 1, "country":1}) # 0 means not include and 1 means include
for student in students:
    print(student)

app = Flask(__name__)
if __name__ == '__main__':
    # for deployment we use the environ
    # to make it work for both production and development
    port = int(os.environ.get("PORT", 5000))
    app.run(debug=True, host='0.0.0.0', port=port)

{'name': 'Asabeneh', 'country': 'Finland'}
{'name': 'David', 'country': 'UK'}
{'name': 'John', 'country': 'Sweden'}
{'name': 'Sami', 'country': 'Finland'}

带查询条件的 Find⚓︎

在 MongoDB 中，find 接受查询对象。我们可以传入查询对象，过滤出想要的文档。

# let's import the flask
from flask import Flask, render_template
import os # importing operating system module

MONGODB_URI = 'mongodb+srv://asabeneh:your_password_goes_here@30daysofpython-twxkr.mongodb.net/test?retryWrites=true&w=majority'
client = pymongo.MongoClient(MONGODB_URI)
db = client['thirty_days_of_python'] # accessing the database

query = {
    "country":"Finland"
}
students = db.students.find(query)

for student in students:
    print(student)


app = Flask(__name__)
if __name__ == '__main__':
    # for deployment we use the environ
    # to make it work for both production and development
    port = int(os.environ.get("PORT", 5000))
    app.run(debug=True, host='0.0.0.0', port=port)

{'_id': ObjectId('5df68a21f106fe2d315bbc8b'), 'name': 'Asabeneh', 'country': 'Finland', 'city': 'Helsinki', 'age': 250}
{'_id': ObjectId('5df68a23f106fe2d315bbc8e'), 'name': 'Sami', 'country': 'Finland', 'city': 'Helsinki', 'age': 25}

带修饰符的查询：

# let's import the flask
from flask import Flask, render_template
import os # importing operating system module
import pymongo

MONGODB_URI = 'mongodb+srv://asabeneh:your_password_goes_here@30daysofpython-twxkr.mongodb.net/test?retryWrites=true&w=majority'
client = pymongo.MongoClient(MONGODB_URI)
db = client['thirty_days_of_python'] # accessing the database

query = {
    "city":"Helsinki"
}
students = db.students.find(query)
for student in students:
    print(student)


app = Flask(__name__)
if __name__ == '__main__':
    # for deployment we use the environ
    # to make it work for both production and development
    port = int(os.environ.get("PORT", 5000))
    app.run(debug=True, host='0.0.0.0', port=port)

{'_id': ObjectId('5df68a21f106fe2d315bbc8b'), 'name': 'Asabeneh', 'country': 'Finland', 'city': 'Helsinki', 'age': 250}
{'_id': ObjectId('5df68a23f106fe2d315bbc8e'), 'name': 'Sami', 'country': 'Finland', 'city': 'Helsinki', 'age': 25}

带修饰符的 Find 查询⚓︎

# let's import the flask
from flask import Flask, render_template
import os # importing operating system module
import pymongo

MONGODB_URI = 'mongodb+srv://asabeneh:your_password_goes_here@30daysofpython-twxkr.mongodb.net/test?retryWrites=true&w=majority'
client = pymongo.MongoClient(MONGODB_URI)
db = client['thirty_days_of_python'] # accessing the database
query = {
    "country":"Finland",
    "city":"Helsinki"
}
students = db.students.find(query)
for student in students:
    print(student)


app = Flask(__name__)
if __name__ == '__main__':
    # for deployment we use the environ
    # to make it work for both production and development
    port = int(os.environ.get("PORT", 5000))
    app.run(debug=True, host='0.0.0.0', port=port)

{'_id': ObjectId('5df68a21f106fe2d315bbc8b'), 'name': 'Asabeneh', 'country': 'Finland', 'city': 'Helsinki', 'age': 250}
{'_id': ObjectId('5df68a23f106fe2d315bbc8e'), 'name': 'Sami', 'country': 'Finland', 'city': 'Helsinki', 'age': 25}

带修饰符的查询：

# let's import the flask
from flask import Flask, render_template
import os # importing operating system module
import pymongo

MONGODB_URI = 'mongodb+srv://asabeneh:your_password_goes_here@30daysofpython-twxkr.mongodb.net/test?retryWrites=true&w=majority'
client = pymongo.MongoClient(MONGODB_URI)
db = client['thirty_days_of_python'] # accessing the database
query = {"age":{"$gt":30}}
students = db.students.find(query)
for student in students:
    print(student)

app = Flask(__name__)
if __name__ == '__main__':
    # for deployment we use the environ
    # to make it work for both production and development
    port = int(os.environ.get("PORT", 5000))
    app.run(debug=True, host='0.0.0.0', port=port)

{'_id': ObjectId('5df68a21f106fe2d315bbc8b'), 'name': 'Asabeneh', 'country': 'Finland', 'city': 'Helsinki', 'age': 250}
{'_id': ObjectId('5df68a23f106fe2d315bbc8c'), 'name': 'David', 'country': 'UK', 'city': 'London', 'age': 34}

# let's import the flask
from flask import Flask, render_template
import os # importing operating system module
import pymongo

MONGODB_URI = 'mongodb+srv://asabeneh:your_password_goes_here@30daysofpython-twxkr.mongodb.net/test?retryWrites=true&w=majority'
client = pymongo.MongoClient(MONGODB_URI)
db = client['thirty_days_of_python'] # accessing the database
query = {"age":{"$gt":30}}
students = db.students.find(query)
for student in students:
    print(student)

{'_id': ObjectId('5df68a23f106fe2d315bbc8d'), 'name': 'John', 'country': 'Sweden', 'city': 'Stockholm', 'age': 28}
{'_id': ObjectId('5df68a23f106fe2d315bbc8e'), 'name': 'Sami', 'country': 'Finland', 'city': 'Helsinki', 'age': 25}

限制文档数量⚓︎

我们可以使用 limit() 方法限制返回的文档数量。

# let's import the flask
from flask import Flask, render_template
import os # importing operating system module
import pymongo

MONGODB_URI = 'mongodb+srv://asabeneh:your_password_goes_here@30daysofpython-twxkr.mongodb.net/test?retryWrites=true&w=majority'
client = pymongo.MongoClient(MONGODB_URI)
db = client['thirty_days_of_python'] # accessing the database
db.students.find().limit(3)

带排序的 Find⚓︎

默认情况下，排序为升序。可以通过添加 -1 参数改为降序。

# let's import the flask
from flask import Flask, render_template
import os # importing operating system module
import pymongo

MONGODB_URI = 'mongodb+srv://asabeneh:your_password_goes_here@30daysofpython-twxkr.mongodb.net/test?retryWrites=true&w=majority'
client = pymongo.MongoClient(MONGODB_URI)
db = client['thirty_days_of_python'] # accessing the database
students = db.students.find().sort('name')
for student in students:
    print(student)


students = db.students.find().sort('name',-1)
for student in students:
    print(student)

students = db.students.find().sort('age')
for student in students:
    print(student)

students = db.students.find().sort('age',-1)
for student in students:
    print(student)

app = Flask(__name__)
if __name__ == '__main__':
    # for deployment we use the environ
    # to make it work for both production and development
    port = int(os.environ.get("PORT", 5000))
    app.run(debug=True, host='0.0.0.0', port=port)

升序

{'_id': ObjectId('5df68a21f106fe2d315bbc8b'), 'name': 'Asabeneh', 'country': 'Finland', 'city': 'Helsinki', 'age': 250}
{'_id': ObjectId('5df68a23f106fe2d315bbc8c'), 'name': 'David', 'country': 'UK', 'city': 'London', 'age': 34}
{'_id': ObjectId('5df68a23f106fe2d315bbc8d'), 'name': 'John', 'country': 'Sweden', 'city': 'Stockholm', 'age': 28}
{'_id': ObjectId('5df68a23f106fe2d315bbc8e'), 'name': 'Sami', 'country': 'Finland', 'city': 'Helsinki', 'age': 25}

降序

{'_id': ObjectId('5df68a23f106fe2d315bbc8e'), 'name': 'Sami', 'country': 'Finland', 'city': 'Helsinki', 'age': 25}
{'_id': ObjectId('5df68a23f106fe2d315bbc8d'), 'name': 'John', 'country': 'Sweden', 'city': 'Stockholm', 'age': 28}
{'_id': ObjectId('5df68a23f106fe2d315bbc8c'), 'name': 'David', 'country': 'UK', 'city': 'London', 'age': 34}
{'_id': ObjectId('5df68a21f106fe2d315bbc8b'), 'name': 'Asabeneh', 'country': 'Finland', 'city': 'Helsinki', 'age': 250}

带查询条件的更新⚓︎

我们将使用 update_one() 方法更新一条记录。它接受两个对象：一个是查询条件，另一个是新对象。第一个人 Asabeneh 的年龄很不合理，让我们更新 Asabeneh 的年龄。

# let's import the flask
from flask import Flask, render_template
import os # importing operating system module
import pymongo

MONGODB_URI = 'mongodb+srv://asabeneh:your_password_goes_here@30daysofpython-twxkr.mongodb.net/test?retryWrites=true&w=majority'
client = pymongo.MongoClient(MONGODB_URI)
db = client['thirty_days_of_python'] # accessing the database

query = {'age':250}
new_value = {'$set':{'age':38}}

db.students.update_one(query, new_value)
# lets check the result if the age is modified
for student in db.students.find():
    print(student)


app = Flask(__name__)
if __name__ == '__main__':
    # for deployment we use the environ
    # to make it work for both production and development
    port = int(os.environ.get("PORT", 5000))
    app.run(debug=True, host='0.0.0.0', port=port)

{'_id': ObjectId('5df68a21f106fe2d315bbc8b'), 'name': 'Asabeneh', 'country': 'Finland', 'city': 'Helsinki', 'age': 38}
{'_id': ObjectId('5df68a23f106fe2d315bbc8c'), 'name': 'David', 'country': 'UK', 'city': 'London', 'age': 34}
{'_id': ObjectId('5df68a23f106fe2d315bbc8d'), 'name': 'John', 'country': 'Sweden', 'city': 'Stockholm', 'age': 28}
{'_id': ObjectId('5df68a23f106fe2d315bbc8e'), 'name': 'Sami', 'country': 'Finland', 'city': 'Helsinki', 'age': 25}

当我们想一次更新多条文档时，使用 update_many() 方法。

删除文档⚓︎

delete_one() 方法删除一条文档。delete_one() 接受一个查询对象参数，只会删除第一条匹配项。让我们从集合中删除一个 John。

# let's import the flask
from flask import Flask, render_template
import os # importing operating system module
import pymongo

MONGODB_URI = 'mongodb+srv://asabeneh:your_password_goes_here@30daysofpython-twxkr.mongodb.net/test?retryWrites=true&w=majority'
client = pymongo.MongoClient(MONGODB_URI)
db = client['thirty_days_of_python'] # accessing the database

query = {'name':'John'}
db.students.delete_one(query)

for student in db.students.find():
    print(student)
# lets check the result if the age is modified
for student in db.students.find():
    print(student)


app = Flask(__name__)
if __name__ == '__main__':
    # for deployment we use the environ
    # to make it work for both production and development
    port = int(os.environ.get("PORT", 5000))
    app.run(debug=True, host='0.0.0.0', port=port)

{'_id': ObjectId('5df68a21f106fe2d315bbc8b'), 'name': 'Asabeneh', 'country': 'Finland', 'city': 'Helsinki', 'age': 38}
{'_id': ObjectId('5df68a23f106fe2d315bbc8c'), 'name': 'David', 'country': 'UK', 'city': 'London', 'age': 34}
{'_id': ObjectId('5df68a23f106fe2d315bbc8e'), 'name': 'Sami', 'country': 'Finland', 'city': 'Helsinki', 'age': 25}

可以看到，John 已从集合中删除。

当我们想删除多条文档时，使用 delete_many() 方法，它接受一个查询对象。若向 delete_many({}) 传入空查询对象，则会删除集合中的所有文档。

删除集合⚓︎

使用 drop() 方法可以从数据库中删除一个集合。

# let's import the flask
from flask import Flask, render_template
import os # importing operating system module
import pymongo

MONGODB_URI = 'mongodb+srv://asabeneh:your_password_goes_here@30daysofpython-twxkr.mongodb.net/test?retryWrites=true&w=majority'
client = pymongo.MongoClient(MONGODB_URI)
db = client['thirty_days_of_python'] # accessing the database
db.students.drop()

现在，我们已从数据库中删除了 students 集合。