Python MongoDB - 查询

您可以使用find()方法读取/检索MongoDB中存储的文档。此方法以非结构化的方式检索并显示MongoDB中的所有文档。

语法

以下是find()方法的语法。

>db.CollectionName.find()

示例

假设我们已经使用以下查询将3个文档插入到名为testDB的数据库中的名为sample的集合中：

> use testDB
> db.createCollection("sample")
> data = [
   {"_id": "1001", "name" : "Ram", "age": "26", "city": "Hyderabad"},
   {"_id": "1002", "name" : "Rahim", "age" : 27, "city" : "Bangalore" },
   {"_id": "1003", "name" : "Robert", "age" : 28, "city" : "Mumbai" }
]
> db.sample.insert(data)

您可以使用find()方法检索插入的文档，如下所示：

> use testDB
switched to db testDB
> db.sample.find()
{ "_id" : "1001", "name" : "Ram", "age" : "26", "city" : "Hyderabad" }
{ "_id" : "1002", "name" : "Rahim", "age" : 27, "city" : "Bangalore" }
{ "_id" : "1003", "name" : "Robert", "age" : 28, "city" : "Mumbai" }
>

您还可以使用findOne()方法检索集合中的第一个文档，如下所示：

> db.sample.findOne()
{ "_id" : "1001", "name" : "Ram", "age" : "26", "city" : "Hyderabad" }

使用python检索数据(find)

pymongo的find_One()方法用于根据您的查询检索单个文档，如果没有匹配项，此方法将不返回任何内容；如果您没有使用任何查询，它将返回集合的第一个文档。

当您只需要检索一个结果文档，或者您确定您的查询只返回一个文档时，此方法非常方便。

示例

以下python示例检索集合的第一个文档：

from pymongo import MongoClient

#Creating a pymongo client
client = MongoClient('localhost', 27017)

#Getting the database instance
db = client['mydatabase']

#Creating a collection
coll = db['example']

#Inserting document into a collection
data = [
   {"_id": "101", "name": "Ram", "age": "26", "city": "Hyderabad"},
   {"_id": "102", "name": "Rahim", "age": "27", "city": "Bangalore"},
   {"_id": "103", "name": "Robert", "age": "28", "city": "Mumbai"}
]
res = coll.insert_many(data)
print("Data inserted ......")
print(res.inserted_ids)

#Retrieving the first record using the find_one() method
print("First record of the collection: ")
print(coll.find_one())

#Retrieving a record with is 103 using the find_one() method
print("Record whose id is 103: ")
print(coll.find_one({"_id": "103"}))

输出

Data inserted ......
['101', '102', '103']
First record of the collection:
{'_id': '101', 'name': 'Ram', 'age': '26', 'city': 'Hyderabad'}
Record whose id is 103:
{'_id': '103', 'name': 'Robert', 'age': '28', 'city': 'Mumbai'}

要在单个查询（find方法的单次调用）中获取多个文档，您可以使用pymongo的find()方法。如果没有传递任何查询，这将返回集合的所有文档；如果您向此方法传递了查询，它将返回所有匹配的文档。

示例

#Getting the database instance
db = client['myDB']

#Creating a collection
coll = db['example']

#Inserting document into a collection
data = [
   {"_id": "101", "name": "Ram", "age": "26", "city": "Hyderabad"},
   {"_id": "102", "name": "Rahim", "age": "27", "city": "Bangalore"},
   {"_id": "103", "name": "Robert", "age": "28", "city": "Mumbai"}
]
res = coll.insert_many(data)
print("Data inserted ......")

#Retrieving all the records using the find() method
print("Records of the collection: ")
for doc1 in coll.find():
print(doc1)

#Retrieving records with age greater than 26 using the find() method
print("Record whose age is more than 26: ")
for doc2 in coll.find({"age":{"$gt":"26"}}):
print(doc2)

输出

Data inserted ......
Records of the collection:
{'_id': '101', 'name': 'Ram', 'age': '26', 'city': 'Hyderabad'}
{'_id': '102', 'name': 'Rahim', 'age': '27', 'city': 'Bangalore'}
{'_id': '103', 'name': 'Robert', 'age': '28', 'city': 'Mumbai'}
Record whose age is more than 26:
{'_id': '102', 'name': 'Rahim', 'age': '27', 'city': 'Bangalore'}
{'_id': '103', 'name': 'Robert', 'age': '28', 'city': 'Mumbai'}