MongoDB Basics

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databases/MongoDB_Basics.md
May 21, 2014
Databases
#commands #mongodb #cheatsheet

Basic Commands

  • show dbs Show databases
  • use dbName Connect/Select database
  • use dbName Create database (MongoDB doesn’t actually create a db until we start storing documents, so although you now have the db bookmarks, it’s not actually saved anywhere until we put some data in it. Same goes for collectons )
  • db show the db you are using
  • doc show the document content

NoSQL Database Terms

MongoDB MySQL
Collections Tables
Documents Rows
Fields (key:value pairs) Columns

Adding Data

There are two methods. One uses .insert()

db.links.insert({ title: "Courses", url: "http://tutsplus.com", comment: "advanced programming video courses", tag: ["tutorials", "dev "], saved_on: new Date() });

and the other us saving an empty document and then adding data to it. e.g:

var doc = {};
doc.title = '';
doc.url = '';
doc.comment = '';
doc.tags = '';
doc.saved_on = new Date;

adding sub-objects inside of objects

doc.meta = {}
doc.meta.browser = 'Google Chrome 31'
doc.meta.OS = 'Mac OS 10.9.2'

Saving and Updating data

  • db.links.save(doc) save all data in the doc collection to the links database
  • db.links.update()

Methods

  • .insert() add data
  • .count() show the number of collections/documents
  • .date() shows the date the data was entered
  • .find() find with no parameters given will just output all data, e.g: - db.links.find()
  • .save()
  • .update()
  • .forEach(printjson); print documents nicely formatted e.g: db.links.find()- .forEach(printjson);
  • .getTimestap() use this method on an _id to get the time the object was created.

Object IDs

This _id or ObjectId object field is immutable and unique. You can’t have two documents with the same _id

  • 12 byte value
  • BSON data type
  • based on the hostname of the machine, the prcess id of the server process, the time the record was saved and a random incrementing number.
  • since they are based on the time they are created, we can get the time an object was created by its ID. We don’t need the created_at or saved_at fields in MongoDB because the ID already has that info.
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