MongoDB with pyMongo II (Connecting and accessing)

List of MongoDB with PyMongo

1. MongoDB with PyMongo I - Installing MongoDB
2. MongoDB with PyMongo II - Connecting and accessing MongoDB
3. MongoDB with pyMongo III - Range Querying MongoDB
4. MongoDB RESTful API with Flask

The first step when working with PyMongo is to create a MongoClient against the running mongod instance:

>>> from pymongo import MongoClient
>>> client = MongoClient()

We're now connected on the default host and port. We can also specify the host and port explicitly, as follows:

>>> client = MongoClient('localhost', 27017)

or MongoDB URI format:

>>> client = MongoClient('mongodb://localhost:27017/')

This MongoClient represents the connection to the MongoDB instance that runs on port 27017 on the localhost.

With a single instance of MongoDB, we can use multiple independent databases. Using PyMongo, we can access databases via attribute style access on MongoClient instances. MongoDB creates new databases implicitly upon their first use.

>>> mydb = client.test_database_1

Note that we can also use dictionary style access instead:

>>> mydb = client['test_database_1']

note: initially I used dash('-') for the database name but now it doesn't allow dash. So, I used underscore('_') instead.

We call a group of documents stored in MongoDB a collection. It is the equivalent of a table in a RDBMS. We can access a collection in PyMongo the same as we access a database:

>>> my_collection = mydb.test-database-1

Or via dictionary style access:

my_collection = mydb['test-database-1']

Note on the lazy creation of MongoDB:
Collections and databases are created when the first document is inserted into them. So, none of the above commands have actually performed any operations on the MongoDB server.

Though the data in MongoDB is stored by JSON-style, PyMongo use dictionaries to store documents. The following is a sample document:

>>> import datetime
>>> myrecord = {"author": "Duke",
...           "title" : "PyMongo 101",
...           "tags" : ["MongoDB", "PyMongo", "Tutorial"],
...           "date" : datetime.datetime.utcnow()
...            }

Note that we used the native Python types such as datetime.datetime instances. But it will be automatically converted to and from the appropriate BSON types. BSON is a binary-encoded serialization of JSON-like documents. BSON is designed to be lightweight, traversable, and efficient. BSON, like JSON, supports the embedding of objects and arrays within other objects and arrays.

For more information about BSON, visit here.

we can use the insert() method to insert a document into our collection:

>>> record_id = mydb.mytable.insert(myrecord)
>>> record_id
ObjectId('5659393d312f910b5b05c18a')

At the insert(), a special key, _id is automatically added if the document doesn't already contain an _id key which must be unique across the collection.

After inserting the first document, the mytable collection has actually been created on the server as we can see below:

>>> mydb.collection_names()
[u'system.indexes', u'mytable']

Here is the file:

# mongo1.py

from pymongo import MongoClient

client = MongoClient('mongodb://localhost:27017/')

# data base name : 'test-database-1'
mydb = client['test-database-1']

import datetime

myrecord = {
        "author": "Duke",
        "title" : "PyMongo 101",
        "tags" : ["MongoDB", "PyMongo", "Tutorial"],
        "date" : datetime.datetime.utcnow()
        }

record_id = mydb.mytable.insert(myrecord)

print record_id
print mydb.collection_names()

Let's could have run the file rather than typing each command line:

$ python mongo1.py

We can check our database and collection using MongoDB Management tool : robomongo:

We can insert several records at one shot by running the following script:

# mongo2.py

from pymongo import MongoClient

client = MongoClient('mongodb://localhost:27017/')
mydb = client['test-database-1']

import datetime

myrecord2 = [
        { "author": "Duke II",
          "title" : "PyMongo II 101",
          "tags" : ["MongoDB II", "PyMongo II", "Tutorial II"],
          "date" : datetime.datetime.utcnow() },
        { "author": "Duke III",
          "title" : "PyMongo III 101",
          "tags" : ["MongoDB III", "PyMongo III", "Tutorial III"],
          "date" : datetime.datetime.utcnow() }
        ]

mydb.mytable.insert(myrecord2)

print mydb.collection_names()

List of MongoDB with PyMongo

1. MongoDB with PyMongo I - Installing MongoDB
2. MongoDB with PyMongo II - Connecting and accessing MongoDB
3. MongoDB with pyMongo III - Range Querying MongoDB
4. MongoDB RESTful API with Flask