MongoDB week2 Notes

MongoDB’s CRUD operations exist as methods/functions in programming language APIs, not as a separated language.

db — current database

db.people.insert( ) — insert into collections

_id — the unique filed for all documents inserted into database, it is a primary key field, and it is immutable

The objectID is a global unique identifier, which is used for __id

db.people.findOne( ) — return randomly one document

db.people.findOne( ) || db.people.find( )

• the first argument specific the criteria to match, like the WHERE clause
• the second argument specific what field to return, like the SELECT clause

db.people.find( ) — find all documents in people collection

db.people.find( ).pretty( ) — change the format to show the result

db.people.find( { score : { $gt : 95 } } ) — query operator

db.people.find( { profession : { $exists : true } } ); — query on the structure of document

db.people.find( { name : { $type : 2 } } ); — query on the type of fields

db.people.find( { name : { $regex : “a” } } ); — regular expression matching on string

{ $or : [query1, query2, … , queryn] }

{ $and : [query1, query2, … , queryn] }

db.accounts.find( { favorites : “beer” } ) — query if an array contains the specific value, only check the top level and no recursion on the nested sub-documents.

db.accounts.find( { favorites : { $all : [ “beer”, “pretzels” ] } } ) — favorites contains all elements in the array, the order does not matter

db.accounts.find( { name : { $in : [ “xxx”, “yyy”] } } ) — the document which name is in the array, either xxx or yyy

db.users.find( { “email.work” : “xxxx” } ) — dot notation, allows to query for the embedded document

cursor.hasNext( ) — return true as long as there’s another document to visit on this cursor

cursor.next( ) — return next document to be visited

cursor.limit( 5 ) — limit the number of the document of the cursor, instruct the server to return specific number of document when cursor start to iterate

cursor.sort( { name : -1 } ) || cursor.skip( ) 

we could not modify the cursor once we have called hasNext( ) or next( ). limit, sort and skip are executed in server side not client side.

sort —> skip —> limit

db.scores.count( { xxx : yyy } ) — count the document

db.people.update( { name : “Smith” }, { name : “Tomas”, Salary : 50000 }) — the document which name is Smith would be replaced by the second argument which is a new document.

db.people.update( { name : “Smith” }, { $set : { name : “Tomas” } } ) — update the field only, if the field does not exist, it will be created

use $inc to increase the value of a specific field

db.people.update( { name : “Smith” }, { $unset : { professional : 1 } } ) — remove a field in a document

db.array.update( { xxx : yyy }, { $set : { “array.index” : zzz } } ) — use dot notation to specify the element in the array try to change

use $push to add an element into the array from the rightmost place

use $pop to remove the rightmost element int the array

use $pushAll to add append an array from the rightmost place

use $pull to remove an element from the array regardless of its position

use $pullAll to remove a list of element from the array

use $addToSet to treat the array as a set, if duplicates exist, it will do nothing

db.people.update( { }, { }, { upset : true } ) — insert a new document if the document does not exist

db.people.update( { }, { }, { multi : true} ) — update multiple documents

db.people.remove( { } ) — remove a document that matches the specific criteria

Nodejs

var MongoClient = require(‘mongodb’).MongoClient;

MongoClient.connect( ‘connect string here’, function(err db) { } )

db.collection( ‘collection name’ ).findOne( query, function(err, doc) { } )

db.collection( ‘collection name’ ).find( query ).toArray(function( err, docs ) { } )

var cursor = db.collection( ‘collection name’ ).find( query );

cursor.each( function( err, doc ) { } ) 

.find( ) will create a cursor object, only when the cursor call .each( ) or .toArray( ), it starts to retrieves data from database, the database will not return the entire result but a batch of the result

db.collection( ‘collection name’ ).find( query, projection )

cursor.sort( [ [ ‘grade’ , 1 ], [ ‘student’ , -1 ] ] ) —> use array in order to avoid the rearrange of the elements

db.collection( ‘collection name’ ).insert( doc, function( err, inserted ) { } )

db.collection( ‘collection name’ ).update( query, operator, options, function( err, updated ) { } )

we could not mix $operators with normal fields

db.collection( ‘collection name’ ).save( doc, function( err, saved ) { } ) — check to see if the doc exist (_id), if not, then a new document would be inserted otherwise, replacement would be done

findAndModify( query, sort, operator, option, callback ) — atomically find and returns the document, no two client would conflict here on the document

Java 

The parameter of all method is DBObject, which is used to represent a document. — BasicDBObject

MongoClient client = new MongoClient( )

DB courseDB = client.getDB(“xxx”)

DBCollection collection = courseDB.getCollection(“xxx”)