Python Data Access 简明教程

Python MongoDB - Find

您可以使用 find() 方法读/取从 MongoDB 中存储的文档。此方法以非结构化方式检索和显示 MongoDB 中的所有文档。

You can read/retrieve stored documents from MongoDB using the find() method. This method retrieves and displays all the documents in MongoDB in a non-structured way.

Syntax

以下是 find() 方法的语法。

Following is the syntax of the find() method.

>db.CollectionName.find()

Example

假设我们已使用以下查询将 3 个文档插入到名为 testDB 的数据库中一个名为 sample 的集合中 -

Assume we have inserted 3 documents into a database named testDB in a collection named sample using the following queries −

> 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() 方法检索已插入的文档，如下所示 -

You can retrieve the inserted documents using the find() method as −

> 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 -

You can also retrieve first document in the collection using the findOne() method as −

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

Retrieving data (find) using python

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，如果您未使用任何查询，它将返回集合的第一个文档。

The find_One() method of pymongo is used to retrieve a single document based on your query, in case of no matches this method returns nothing and if you doesn’t use any query it returns the first document of the collection.

每当您需要仅检索结果中的一个文档或确信您的查询只返回一个文档时，此方法都派上用场。

This method comes handy whenever you need to retrieve only one document of a result or, if you are sure that your query returns only one document.

Example

以下 python 示例检索集合的第一个文档 -

Following python example retrieve first document of a collection −

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"}))

Output

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'}

要通过单个查询（find 方法的单个调用）获取多个文档，可以使用 pymongo 的 find() 方法。如果没有传递任何查询，它将返回集合的所有文档，如果您已将查询传递给此方法，它将返回所有匹配的文档。

To get multiple documents in a single query (single call od find method), you can use the find() method of the pymongo. If haven’t passed any query, this returns all the documents of a collection and, if you have passed a query to this method, it returns all the matched documents.

Example

#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)

Output

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'}