MongoDB

Python can be used in database applications.

One of the most popular NoSQL database is MongoDB.

MongoDB stores data in JSON-like documents, which makes the database very flexible and scalable.

To execute code examples,

Download a free MongoDB database at

MongoDB

PyMongo

Python needs a MongoDB driver to access the MongoDB database.

Navigate command line(cmd.exe) and type the following command to download and install “PyMango”.

python -m pip install pymongo

Test PyMongo

To test if the installation “pymongo” was successful, create a Python page with the following content:

demo_mongodb_test.py:

import pymongo

If the above code was executed with no errors, "pymongo" is installed and ready to be used.

To create a database in MongoDB, start by creating a MongoClient object, then specify a connection URL with the correct ip address and the name of the database you want to create.

MongoDB will create the database if it does not exist, and make a connection to it.

Example

Create a database called "mydatabase":

import pymongo

myclient = pymongo.MongoClient("mongodb://localhost:27017/")

mydb = myclient["mydatabase"]

Important: In MongoDB, a database is not created until it gets content!

MongoDB waits until you have created a collection (table), with at least one document (record) before it actually creates the database (and collection).

Check if Database Exists

Remember: In MongoDB, a database is not created until it gets content, so if this is your first time creating a database, you should complete the next two chapters (create collection and create document) before you check if the database exists!

You can check if a database exist by listing all databases in you system:

Example

Return a list of your system's databases:

print(myclient.list_database_names())

Or you can check a specific database by name:

Example

Check if "mydatabase" exists:

dblist = myclient.list_database_names()

if "mydatabase" in dblist:

  print("The database exists.")

A collection in MongoDB is the same as a table in SQL databases.

Creating a Collection

To create a collection in MongoDB, use database object and specify the name of the collection you want to create.

MongoDB will create the collection if it does not exist.

Example

Create a collection called "customers":

import pymongo

myclient = pymongo.MongoClient("mongodb://localhost:27017/")

mydb = myclient["mydatabase"]

mycol = mydb["customers"]

Important: In MongoDB, a collection is not created until it gets content!

MongoDB waits until you have inserted a document before it actually creates the collection.

Check if Collection Exists

Remember: In MongoDB, a collection is not created until it gets content, so if this is your first time creating a collection, you should complete the next chapter (create document) before you check if the collection exists!

You can check if a collection exists in a database by listing all collections:

Example

Return a list of all collections in your database:

print(mydb.list_collection_names())

Or you can check a specific collection by name:

Example

Check if the "customers" collection exists:

collist = mydb.list_collection_names()

if "customers" in collist:

  print("The collection exists.")

A document in MongoDB is the same as a record in SQL databases.

Insert Into Collection

To insert a record, or document as it is called in MongoDB, into a collection, we use the insert_one() method.

The first parameter of the insert_one() method is a dictionary containing the name(s) and value(s) of each field in the document you want to insert.

Example

Insert a record in the "customers" collection:

import pymongo

myclient = pymongo.MongoClient("mongodb://localhost:27017/")

mydb = myclient["mydatabase"]

mycol = mydb["customers"]

mydict = { "name": "John", "address": "Highway 37" }

x = mycol.insert_one(mydict)

Return the _id Field

The insert_one() method returns a InsertOneResult object, which has a property, inserted_id, that holds the id of the inserted document.

Example

Insert another record in the "customers" collection, and return the value of the _id field:

mydict = { "name": "Peter", "address": "Lowstreet 27" }

x = mycol.insert_one(mydict)

print(x.inserted_id)

If you do not specify an _id field, then MongoDB will add one for you and assign a unique id for each document.

In the example above no _id field was specified, so MongoDB assigned a unique _id for the record (document).

Insert Multiple Documents

To insert multiple documents into a collection in MongoDB, we use the insert_many() method.

The first parameter of the insert_many() method is a list containing dictionaries with the data you want to insert:

Example

import pymongo

myclient = pymongo.MongoClient("mongodb://localhost:27017/")

mydb = myclient["mydatabase"]

mycol = mydb["customers"]

mylist = [

  { "name": "Amy", "address": "Apple st 652"},

  { "name": "Hannah", "address": "Mountain 21"},

  { "name": "Michael", "address": "Valley 345"},

  { "name": "Sandy", "address": "Ocean blvd 2"},

  { "name": "Betty", "address": "Green Grass 1"},

  { "name": "Richard", "address": "Sky st 331"},

  { "name": "Susan", "address": "One way 98"},

  { "name": "Vicky", "address": "Yellow Garden 2"},

  { "name": "Ben", "address": "Park Lane 38"},

  { "name": "William", "address": "Central st 954"},

  { "name": "Chuck", "address": "Main Road 989"},

  { "name": "Viola", "address": "Sideway 1633"}

]

x = mycol.insert_many(mylist)

#print list of the _id values of the inserted documents:

print(x.inserted_ids)

The insert_many() method returns a InsertManyResult object, which has a property, inserted_ids, that holds the ids of the inserted documents.

Insert Multiple Documents, with Specified IDs

If you do not want MongoDB to assign unique ids for you document, you can specify the _id field when you insert the document(s).

Remember that the values has to be unique. Two documents cannot have the same _id.

Example

import pymongo

myclient = pymongo.MongoClient("mongodb://localhost:27017/")

mydb = myclient["mydatabase"]

mycol = mydb["customers"]

mylist = [

  { "_id": 1, "name": "John", "address": "Highway 37"},

  { "_id": 2, "name": "Peter", "address": "Lowstreet 27"},

  { "_id": 3, "name": "Amy", "address": "Apple st 652"},

  { "_id": 4, "name": "Hannah", "address": "Mountain 21"},

  { "_id": 5, "name": "Michael", "address": "Valley 345"},

  { "_id": 6, "name": "Sandy", "address": "Ocean blvd 2"},

  { "_id": 7, "name": "Betty", "address": "Green Grass 1"},

  { "_id": 8, "name": "Richard", "address": "Sky st 331"},

  { "_id": 9, "name": "Susan", "address": "One way 98"},

  { "_id": 10, "name": "Vicky", "address": "Yellow Garden 2"},

  { "_id": 11, "name": "Ben", "address": "Park Lane 38"},

  { "_id": 12, "name": "William", "address": "Central st 954"},

  { "_id": 13, "name": "Chuck", "address": "Main Road 989"},

  { "_id": 14, "name": "Viola", "address": "Sideway 1633"}

]

x = mycol.insert_many(mylist)

#print list of the _id values of the inserted documents:

print(x.inserted_ids)

In MongoDB we use the find and findOne methods to find data in a collection.

Just like the SELECT statement is used to find data in a table in a MySQL database.

Find One

To select data from a collection in MongoDB, we can use the find_one() method.

The find_one() method returns the first occurrence in the selection.

Example

Find the first document in the customers collection:

import pymongo

myclient = pymongo.MongoClient("mongodb://localhost:27017/")

mydb = myclient["mydatabase"]

mycol = mydb["customers"]

x = mycol.find_one()

print(x)

Find All

To select data from a table in MongoDB, we can also use the find() method.

The find() method returns all occurrences in the selection.

The first parameter of the find() method is a query object. In this example we use an empty query object, which selects all documents in the collection.

No parameters in the find() method gives you the same result as SELECT * in MySQL.

Example

Return all documents in the "customers" collection, and print each document:

import pymongo

myclient = pymongo.MongoClient("mongodb://localhost:27017/")

mydb = myclient["mydatabase"]

mycol = mydb["customers"]

for x in mycol.find():

  print(x)

Return Only Some Fields

The second parameter of the find() method is an object describing which fields to include in the result.

This parameter is optional, and if omitted, all fields will be included in the result.

Example

Return only the names and addresses, not the _ids:

import pymongo

myclient = pymongo.MongoClient("mongodb://localhost:27017/")

mydb = myclient["mydatabase"]

mycol = mydb["customers"]

for x in mycol.find({},{ "_id": 0, "name": 1, "address": 1 }):

  print(x)

You are not allowed to specify both 0 and 1 values in the same object (except if one of the fields is the _id field). If you specify a field with the value 0, all other fields get the value 1, and vice versa:

Example

This example will exclude "address" from the result:

import pymongo

myclient = pymongo.MongoClient("mongodb://localhost:27017/")

mydb = myclient["mydatabase"]

mycol = mydb["customers"]

for x in mycol.find({},{ "address": 0 }):

  print(x)

Example

You get an error if you specify both 0 and 1 values in the same object (except if one of the fields is the _id field):

import pymongo

myclient = pymongo.MongoClient("mongodb://localhost:27017/")

mydb = myclient["mydatabase"]

mycol = mydb["customers"]

for x in mycol.find({},{ "name": 1, "address": 0 }):

  print(x)

Filter the Result

When finding documents in a collection, you can filter the result by using a query object.

The first argument of the find() method is a query object, and is used to limit the search.

Example

Find document(s) with the address "Park Lane 38":

import pymongo

myclient = pymongo.MongoClient("mongodb://localhost:27017/")

mydb = myclient["mydatabase"]

mycol = mydb["customers"]

myquery = { "address": "Park Lane 38" }

mydoc = mycol.find(myquery)

for x in mydoc:

  print(x)

Advanced Query

To make advanced queries you can use modifiers as values in the query object.

E.g. to find the documents where the "address" field starts with the letter "S" or higher (alphabetically), use the greater than modifier: {"$gt": "S"}:

Example

Find documents where the address starts with the letter "S" or higher:

import pymongo

myclient = pymongo.MongoClient("mongodb://localhost:27017/")

mydb = myclient["mydatabase"]

mycol = mydb["customers"]

myquery = { "address": { "$gt": "S" } }

mydoc = mycol.find(myquery)

for x in mydoc:

  print(x)

Filter With Regular Expressions

You can also use regular expressions as a modifier.

Regular expressions can only be used to query strings.

To find only the documents where the "address" field starts with the letter "S", use the regular expression {"$regex": "^S"}:

Example

Find documents where the address starts with the letter "S":

import pymongo

myclient = pymongo.MongoClient("mongodb://localhost:27017/")

mydb = myclient["mydatabase"]

mycol = mydb["customers"]

myquery = { "address": { "$regex": "^S" } }

mydoc = mycol.find(myquery)

for x in mydoc:

  print(x)

Sort the Result

Use the sort() method to sort the result in ascending or descending order.

The sort() method takes one parameter for "fieldname" and one parameter for "direction" (ascending is the default direction).

Example

Sort the result alphabetically by name:

import pymongo

myclient = pymongo.MongoClient("mongodb://localhost:27017/")

mydb = myclient["mydatabase"]

mycol = mydb["customers"]

mydoc = mycol.find().sort("name")

for x in mydoc:

  print(x)

Sort Descending

Use the value -1 as the second parameter to sort descending.

sort("name", 1) #ascending

sort("name", -1) #descending

Example

Sort the result reverse alphabetically by name:

import pymongo

myclient = pymongo.MongoClient("mongodb://localhost:27017/")

mydb = myclient["mydatabase"]

mycol = mydb["customers"]

mydoc = mycol.find().sort("name", -1)

for x in mydoc:

  print(x)

Delete Document

To delete one document, we use the delete_one() method.

The first parameter of the delete_one() method is a query object defining which document to delete.

Note: If the query finds more than one document, only the first occurrence is deleted.

Example

Delete the document with the address "Mountain 21":

import pymongo

myclient = pymongo.MongoClient("mongodb://localhost:27017/")

mydb = myclient["mydatabase"]

mycol = mydb["customers"]

myquery = { "address": "Mountain 21" }

mycol.delete_one(myquery)

Delete Many Documents

To delete more than one document, use the delete_many() method.

The first parameter of the delete_many() method is a query object defining which documents to delete.

Example

Delete all documents were the address starts with the letter S:

import pymongo

myclient = pymongo.MongoClient("mongodb://localhost:27017/")

mydb = myclient["mydatabase"]

mycol = mydb["customers"]

myquery = { "address": {"$regex": "^S"} }

x = mycol.delete_many(myquery)

print(x.deleted_count, " documents deleted.")

Delete All Documents in a Collection

To delete all documents in a collection, pass an empty query object to the delete_many() method:

Example

Delete all documents in the "customers" collection:

import pymongo

myclient = pymongo.MongoClient("mongodb://localhost:27017/")

mydb = myclient["mydatabase"]

mycol = mydb["customers"]

x = mycol.delete_many({})

print(x.deleted_count, " documents deleted.")

Delete Collection

You can delete a table, or collection as it is called in MongoDB, by using the drop() method.

Example

Delete the "customers" collection:

import pymongo

myclient = pymongo.MongoClient("mongodb://localhost:27017/")

mydb = myclient["mydatabase"]

mycol = mydb["customers"]

mycol.drop()

The drop() method returns true if the collection was dropped successfully, and false if the collection does not exist.

Update Collection

You can update a record, or document as it is called in MongoDB, by using the update_one() method.

The first parameter of the update_one() method is a query object defining which document to update.

Note: If the query finds more than one record, only the first occurrence is updated.

The second parameter is an object defining the new values of the document.

Example

Change the address from "Valley 345" to "Canyon 123":

import pymongo

myclient = pymongo.MongoClient("mongodb://localhost:27017/")

mydb = myclient["mydatabase"]

mycol = mydb["customers"]

myquery = { "address": "Valley 345" }

newvalues = { "$set": { "address": "Canyon 123" } }

mycol.update_one(myquery, newvalues)

#print "customers" after the update:

for x in mycol.find():

  print(x)

Update Many

To update all documents that meets the criteria of the query, use the update_many() method.

Example

Update all documents where the address starts with the letter "S":

import pymongo

myclient = pymongo.MongoClient("mongodb://localhost:27017/")

mydb = myclient["mydatabase"]

mycol = mydb["customers"]

myquery = { "address": { "$regex": "^S" } }

newvalues = { "$set": { "name": "Minnie" } }

x = mycol.update_many(myquery, newvalues)

print(x.modified_count, "documents updated.")

Limit the Result

To limit the result in MongoDB, we use the limit() method.

The limit() method takes one parameter, a number defining how many documents to return.

Consider you have a "customers" collection:

Customers

{'_id': 1, 'name': 'John', 'address': 'Highway37'}

{'_id': 2, 'name': 'Peter', 'address': 'Lowstreet 27'}

{'_id': 3, 'name': 'Amy', 'address': 'Apple st 652'}

{'_id': 4, 'name': 'Hannah', 'address': 'Mountain 21'}

{'_id': 5, 'name': 'Michael', 'address': 'Valley 345'}

{'_id': 6, 'name': 'Sandy', 'address': 'Ocean blvd 2'}

{'_id': 7, 'name': 'Betty', 'address': 'Green Grass 1'}

{'_id': 8, 'name': 'Richard', 'address': 'Sky st 331'}

{'_id': 9, 'name': 'Susan', 'address': 'One way 98'}

{'_id': 10, 'name': 'Vicky', 'address': 'Yellow Garden 2'}

{'_id': 11, 'name': 'Ben', 'address': 'Park Lane 38'}

{'_id': 12, 'name': 'William', 'address': 'Central st 954'}

{'_id': 13, 'name': 'Chuck', 'address': 'Main Road 989'}

{'_id': 14, 'name': 'Viola', 'address': 'Sideway 1633'}

Example

Limit the result to only return 5 documents:

import pymongo

myclient = pymongo.MongoClient("mongodb://localhost:27017/")

mydb = myclient["mydatabase"]

mycol = mydb["customers"]

myresult = mycol.find().limit(5)

#print the result:

for x in myresult:

  print(x)