http://www.techbeamers.com/python-mongodb-programming-tutorial/

#python #mongo #pymongo #nosql

In order to connect to MongoDB replica set in Python you can give all server node addersses to MongoClient. Addresses passed to MongoClient() are called the seeds. As long as at least one of the seeds is online, MongoClient discovers all the members in the replica set, and determines which is the current primary and which are secondaries or arbiters.


Sample usages:

>>> MongoClient('localhost', replicaset='foo')
     MongoClient(host=['localhost:27017'], replicaset='foo', ...)
 >>> MongoClient('localhost:27018', replicaset='foo')
     MongoClient(['localhost:27018'], replicaset='foo', ...)
 >>> MongoClient('localhost', 27019, replicaset='foo')
     MongoClient(['localhost:27019'], replicaset='foo', ...)
 >>> MongoClient('mongodb://localhost:27017,localhost:27018/?replicaSet=foo')
     MongoClient(['localhost:27017', 'localhost:27018'], replicaset='foo', ...)

Read full details here:

- http://api.mongodb.com/python/current/examples/high_availability.html#connecting-to-a-replica-set


#database #mongodb #mongo #replica_set #replication #pymongo #arbiter #master #primary #slave

Secondary Reads

By default an instance of MongoClient sends queries to the primary member of the replica set. To use secondaries for queries we have to change the read preference:

>>> client = MongoClient(
 ...     'localhost:27017',
 ...     replicaSet='foo',
 ...     readPreference='secondaryPreferred')
 >>> client.read_preference
 SecondaryPreferred(tag_sets=None)

Now all queries will be sent to the secondary members of the set. If there are no secondary members the primary will be used as a fallback. If you have queries you would prefer to never send to the primary you can specify that using the secondary read preference.

#mongodb #replica_set #replication #secondary #slave #pymongo

If you have mongoDB as your database and you query on DB from an external network, make sure you have SSL in place. By not using SSL everyone can evesdrop on the network data which is transmitted in between.

Read the below article to set SSL on server side:

- https://docs.mongodb.com/manual/tutorial/configure-ssl/

Now in order to set SSL=True in mongo python driver head over to link below to read more on:

- http://api.mongodb.com/python/current/examples/tls.html

#mongodb #ssl #tls #pymongo

Now to make you MongoDB client connection secure just pass ssl=True:

# test_mongodb_ssl.py
 client = pymongo.MongoClient('example.com', ssl=True)

When you run this script check your mongoDB logs (usually in /var/log/mongodb/mongod.log`). The thing you should take into account is that when you pass `ssl=True parameter to MongoClient you just should see the below log (ip addresses wil vary):

I NETWORK  [listener] connection accepted from 172.15.141.162:50761 #49 (39 connections now open)
 I NETWORK  [conn49] end connection 172.15.141.162:50761 (38 connections now open)

Now remove ssl=True from MongoClient or pass ssl=False. If you now run your test script, you would see something like below in mongod.log:

I NETWORK  [listener] connection accepted from 172.15.141.162:50762 #50 (39 connections now open)
 I NETWORK  [conn50] SSL mode is set to 'preferred' and connection 50 to 172.15.141.162:50762 is not using SSL.

It says that SSL mode in mongo config is set to preferSSL and your new connection to mongo is not using it.

YOU NEED TO BE CAUTIOUS that we have created our SSL ourselves and it is vulnerable to man in the middle attack. For production usage purchase you SSL/TLS certifcate.

#mongodb #mongo #ssl #pymongo

in pymongo you can give name to your connections. This definitely helps to debug issues or trace logs when seeing mongoDB logs. The
most important part if this scenario is when you are using micro service architecture and you have tens of modules which works independently from each other and send their requests to MongoDB:

mc = pymongo.MongoClient(host, port, appname='YOUR_APP_NAME')

Now if you look at the MongoDB log you would see:

I COMMAND  [conn173140] command MY_DB.users appName: "YOUR_APP_NAME" command: find { find: "deleted_users", filter: {}, sort: {        acquired_date: 1 }, skip: 19973, limit: 1000, $readPreference: { mode: "secondaryPreferred" }, $db: "blahblah" } planSummary:          COLLSCAN keysExamined:0 docsExamined:19973 hasSortStage:1 cursorExhausted:1 numYields:312 nreturned:0 reslen:235 locks:{ Global: {     acquireCount: { r: 626 } }, Database: { acquireCount: { r: 313 } }, Collection: { acquireCount: { r: 313 } } } protocol:op_query 153ms

In the above log you would see YOUR_APP_NAME.


#mongodb #mongo #pymongo #appname

In MongoDB you can use $regex in order to find something based on a regex pattern:

my_col.find({'name': { $regex: '^ali.*' } })

It will find all users that their names start with ali. Now let's say you want to search users based on their phone country code which has a + in its number like +98901.... You need to escape the + character but escape it twice:

my_col.find({'phone': { $regex: '^\\+98.*' } })

#mongoDB #pymongo #regex

Is there a way to create ObjectID from an INT in MongoDB?

import bson

def object_id_from_int(n):
    s = str(n)
    s = '0' * (24 - len(s)) + s
    return bson.ObjectId(s)

def int_from_object_id(obj):
    return int(str(obj))

n = 12345
obj = object_id_from_int(n)
n = int_from_object_id(obj)
print(repr(obj))  # ObjectId('000000000000000000012345')
print(n)  # 12345

#mongodb #objectid #pymongo #python #bson #int