Pymongo如何设置read_preference

Question

我们如何使 PyMongo 从最近读取？此字段 db.read_preference 现在是只读的。

from pymongo import ReplicaSetConnection
from pymongo import ReadPreference

db = ReplicaSetConnection('localhost:27017', replicaSet='rs1')['my_db']
db.read_preference = ReadPreference.NEAREST
db.tag_sets = [{'secondaries': 1}]

Answer 1

您需要将其添加到连接字符串中，如下所示：

db = ReplicaSetConnection('localhost:27017?readPreference=nearest', replicaSet='rs1')['my_db']

或

db = MongoClient("myhost:27017", read_preference=ReadPreference.NEAREST, replicaSet='rs1')['my_db']

无论出于何种原因，您使用的给定语法都失败了，它似乎是旧版 Pymongo 支持的语法。

Answer 2

选项 1（每个连接）：

>>> from pymongo import MongoClient, ReadPreference
>>> db = MongoClient("myhost:27017", read_preference=ReadPreference.NEAREST).test
>>> db.collection.find_one({test:1})

选项 2（每个查询）：

>>> db.collection.find_one({test:1},read_preference=ReadPreference.NEAREST)

Answer 3

PyMongo ReadPreference can also be applied at database, collection or a query level (in addition to within Connection String URI and with the MongoClient).

from pymongo import ReadPreference

# Specifying read preference at database level
db1 = client.testdb1
db2 = client.get_database('testdb2', read_preference=ReadPreference.NEAREST)

# Specifying read preference at collection level
coll2 = db1.coll1.with_options(read_preference=ReadPreference.NEAREST)

# Specifying read preference for a specific query
result = db1.coll1.with_options(read_preference=ReadPreference.NEAREST).find()

请注意，在较低级别（例如，集合）设置的读取首选项将覆盖在上一级（例如，数据库或 mongo 客户端）设置的读取首选项。

Pymongo如何设置read_preference

Pymongo how to set read_preference

python

mongodb

pymongo