mongo.md

MongoDB

Tutorials

Name	Description
Guru99 MongoDB Tutorial	MongoDB Tutorial
Tutorialspoint Tutorial	MongoDB Tutorial

Cheat Sheet

Mongo Shell

I assume the following for the purpose of the examples:

• DB name: usage_patterns

• Collection name: accounts

• DB stats: db.stats()

• Switch to a DB: use usage_patterns

• show collections: show collections

• Count the number of documents in a collection: db.accounts.count()

• Remove all the documents from a collection: db.accounts.remove({})

• Export Mongo DB into JSON file: mongoexport --db=usage_patterns --collection=accounts --out=data.json

Aggregations

• Count the number of documents: db.accounts.aggregate([ { "$count": "number of documents" }])
• Show only the sub element "attachment_uuids": db.accounts.aggregate( [ {$project: {"hosts.attachment_uuids": 1, _id:0}} ] )

Mongo Python

• Add new element to an arrray only if it doesn't exists already

mongo_client.update(
        { "account_number": account_num },
        { "$addToSet": { "hosts": {'hostname': hostname} } }
    )

• Add a new element to an array in sub-document (if it doesn't exists already):

 mongo_client.update_one(
        { "account_number": account_num, "hosts.hostname": hostname },
        { "$addToSet": { "hosts.$.attachment_uuids": attachment_uuid } }
    )