Getting Started with MongoDB and NodeJS

Getting Started With MongoDB and
Node.JS
Jay Runkel
Principal Solutions Architect
jay.runkel@mongodb.com
@jayrunkel

3
GridFS
Driver
GridFS API
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data)
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(1)
fs.files fs.chunks
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6
Goal Today
• Help you get started with MongoDB and Node.JS
• Assumption:
– New to both technologies
– Programming Experience
– Database Experience
• Learn from my newbie confusion

7
Agenda
1. Why Node.JS and MongoDB?
2. Find and Insert
3. Node.JS async, event queue, flow control
4. Controlling multiple threads
– Bulk insert

10
JavaScript and “JSON” throughout
Browser
JavaScript
Node.JS
JavaScriptJSON
BSON (JSON)
BSON
JSON

11
Documents are Rich Data Structures
{
first_name: ‘Paul’,
surname: ‘Miller’,
cell: ‘+447557505611’
city: ‘London’,
location: [45.123,47.232],
Profession: [banking, finance, trader],
cars: [
{ model: ‘Bentley’,
year: 1973,
value: 100000, … },
{ model: ‘Rolls Royce’,
year: 1965,
value: 330000, … }
]
}
Fields can contain an array of sub-documents
Fields
Typed field values
Fields can contain arrays

Do More With Your Data
MongoDB
{
first_name: ‘Paul’,
surname: ‘Miller’,
city: ‘London’,
location: [45.123,47.232],
cars: [
{ model: ‘Bentley’,
year: 1973,
value: 100000, … },
{ model: ‘Rolls Royce’,
year: 1965,
value: 330000, … }
}
}
Rich Queries
Find Paul’s cars
Find everybody in London with a car
built between 1970 and 1980
Geospatial
Find all of the car owners within 5km
of Trafalgar Sq.
Text Search
Find all the cars described as having
leather seats
Aggregation
Calculate the average value of Paul’s
car collection
Map Reduce
What is the ownership pattern of
colors by geography over time?
(is purple trending up in China?)

14
Sample Data
{
"_id" : "20160101000000:UA7549",
"icao" : "UA7549",
"callsign" : "UA7549",
"ts" : ISODate("2016-01-01T05:00:00Z"),
"events" : {
"a" : 1773,
"b" : 258,
"p" : [50,-60],
"s" : 345,
"t" : ISODate("2016-01-01T05:00:00Z"),
"v" : 299
}
}

15
Example: Find Query
• Find a flight status entry for United Airlines Flight 1234
– db.data.findOne({"callsign" : "UA7549"})
• Find a aircraft flying at less than 5000 feet
– db.data.findOne({"events.a" : {$lt : 5000}})
• Set value of note field
– db.data.update({"callsign" : "OY1949"},
{$set : {"note" : "spoke with captain"}})

Retrieve One Document in Node.JS
The Simple Things Don’t Always Seem Easy

17
The synchronous way
var MongoClient = require('mongodb').MongoClient;
var db = MongoClient.connect('mongodb://localhost:27017/adsb');
var col = db.collection('data');
var doc = col.findOne({"callsign" : "UA7549"});
console.log("Here is my doc: %j", doc);
db.close();

18
The synchronous way
var MongoClient = require('mongodb').MongoClient;
var db = MongoClient.connect('mongodb://localhost:27017/adsb');
var doc = col.findOne({"callsign" : "UA7549"});
db.close();

19
It works this way in the mongoshell???
var col = db.getCollection("data");
var doc = col.findOne({"callsign" : "HR9368"});
printjson(doc);

Synchronous vs. Asychronous
Event Loop

21
Synchronous Programming
time
Func1 Func1 IO Func1 Func2 Func2 IO Func2

22
Asynchronous Programming
time
Func1
Func1 IO
Func1Func2
Func2 IO
Func2
IO Processing runs on separate
threads in parallel with main
processing thread

23
Callbacks
col.findOne({"callsign" : "UA7549"}, function (err, doc) {
assert.equal(null, err);
console.log(”All done!”);
• Execute findOne
• When it is done, call the callback function
• Callback function takes two arguments
– err – contains the error message or null
– doc – the result of the findOne call
• “All Done” will be printed before the “Here is my doc…”

24
Event queue
From: http://www.slideshare.net/takingblue/talk-nodejs-andisomorphicjavascript

25
Event queue
From: http://www.slideshare.net/takingblue/talk-nodejs-andisomorphicjavascript
MongoDB

26
Event Queue/Call Stack
function find1234 () {
col.findOne({_id: 1234},
fo1_cb);
find1234();
col.updateMany({color: “blue”},
{$set : {w : 5}}, up1_cb);
col.insert({product: 1234,
cost: 99}, ins1_cb);
console.log(“done”);
Call Stack Driver API
Callback
Queue
Event Loop

27
fo1_cb);
find1234();
{$set : {w : 5}}, up1_cb);
Callback
Queue
Event Loop
find1234()

28
fo1_cb);
find1234();
{$set : {w : 5}}, up1_cb);
Callback
Queue
Event Loop
find1234()
col.findOne()
col.findOne()

29
fo1_cb);
find1234();
{$set : {w : 5}}, up1_cb);
Callback
Queue
Event Loop
col.updateMany()
col.findOne()
col.updateMany()

30
fo1_cb);
find1234();
{$set : {w : 5}}, up1_cb);
Callback
Queue
Event Loop
col.insert()
col.insert()
col.updateMany()
fo1_cb

31
fo1_cb);
find1234();
{$set : {w : 5}}, up1_cb);
Callback
Queue
Event Loop
console.log()
col.updateMany()
fo1_cb ins1_cb

32
fo1_cb);
find1234();
{$set : {w : 5}}, up1_cb);
function fo1_cb () {…}
Callback
Queue
Event Loop
fo1_cb()
col.updateMany()
ins1_cb

33
Callback
Queue
Event Loop
ins1_cb()
up1_cb
fo1_cb);
find1234();
{$set : {w : 5}}, up1_cb);
function ins1_cb () {…}

34
Callback
Queue
Event Loop
up1_cb()
fo1_cb);
find1234();
{$set : {w : 5}}, up1_cb);
function up1_cb () {…}

36
MongoDB Asynchronous Queries
var MongoClient = require('mongodb').MongoClient,
assert = require('assert');
MongoClient.connect('mongodb://localhost:27017/adsb', function (err, db) {
db.close();
});
});

37
Asynchronously
db.close();
});
});
callback

38
Asynchronously
db.close();
});
});
callback

39
This gets ugly fast
var db = MongoClient.connect('mongodb://localhost:27017/adsb', function (err, db) {
col.updateOne({"callsign" : "UA7549"}, {$set : {"note" : "Spoke with the
pilot"}}, {}, function(err, result) {
console.log("Note updated");
db.close();
});
});
});

40
Nested callbacks - yuck
async1(function(input, result1) {
async2(function(result2) {
async5(function(output) {
// do something with output
});
});
});
});
})

41
Solutions
• Break up into modules
• Use a Flow Control library
– async
– Step
• Promises

42
With Flow Control - Step
Step (
function connectToMongoDB (err, db) {
MongoClient.connect('mongodb://
localhost:27017/adsb', this);
},
function findOneDoc(err, db) {
if (err) console.log("Connect: %j",
err);
database = db;
collection = db.collection('data');
collection.findOne(csQuery, {}, this);
},
function updateDoc(err, doc) {
if (err) console.log("Find One: %j",
err);
collection.updateOne(csQuery,
{$inc : {"timesViewed" : 1}},{},this);
},
function findOneDoc2 (err, result) {
if (err)
console.log("Update error: %j", err);
collection.findOne(csQuery, {},
this);
},
function closeConnection(err, doc) {
if (err)
console.log("FindOne Doc: %j", err);
console.log("Note updated: %j",
doc);
database.close();
}
);

43
With Flow Control
Step (
},
err);
database = db;
},
err);
},
if (err)
this);
},
if (err)
doc);
database.close();
}

44
With Flow Control
Step (
},
err);
database = db;
},
err);
},
if (err)
this);
},
if (err)
doc);
database.close();
}

45
You can also execute in parallel
Step (
MongoClient.connect('mongodb://localhost:27017/adsb', this);
},
function executeParallel (err, db) {
if (err) console.log("Connect: %j", err);
var collection = db.collection('data');
database = db;
collection.findOne(csQuery, {}, this.parallel());
collection.updateOne(csQuery, {$inc : {"timesViewed" : 1}}, {}, this.parallel());
collection.findOne(csQuery, {}, this.parallel());
},
function closeConnection(err, doc1, upResult, doc2) {
if (err) console.log("Error: %j", err);
console.log("Here is doc1: %j", doc1);
console.log("Incremented: %j", upResult);
console.log("Here is doc2: %j", doc2);
database.close();
}
);

How do you deal with multiple find results?

47
Find Many - Cursor
• This works in the MongoShell
var cursor = col.find({"events.a" : {$gt : 5000}});
while (cursor.hasNext()) {
printjson(cursor.next());
}

48
Find Many - Cursor
• This works in the MongoShell
var cursor = col.find({"events.a" : {$gt : 5000}});
while (cursor.hasNext()) {
printjson(cursor.next());
}
• It does not work in Node.JS
• The MongoDB driver retrieves documents in batches from MongoDB
– Retrieving a new batch is asynchronous

49
Find Many - Streams
MongoClient.connect("mongodb://localhost:27017/adsb", function (err, db) {
var col = db.collection('data')
var stream = col.find({"events.a" : {$gt : 5000}}).stream();
stream.on('data', function(doc) {
console.log("Doc: %j", doc);
});
stream.on('error', function (doc) {
console.log("Query failed: %j", doc);
});
stream.on('end', function() {
console.log("All data retrieved.");
db.close();
});
});

50
Find Many - Streams
MongoClient.connect("mongodb://localhost:27017/adsb", function (err, db) {
var col = db.collection('data')
var stream = col.find({"events.a" : {$gt : 5000}}).stream();
stream.on('data', function(doc) {
console.log("Doc: %j", doc);
});
stream.on('error', function (doc) {
console.log("Query failed: %j", doc);
});
stream.on('end', function() {
console.log("All data retrieved.");
db.close();
});
});
‘data’ callback invoked
for each document

51
What about insert?
col.insert({x: 1, y: 2, z: 3},
{},
function (err, result) {
console.log("Insert Complete");
db.close();
});
});

52
What if I have to insert 100M documents?
for (i = 1; i <= 100000000; i++) {
col.insert({x: i, y: 2, z: 3},
{},
});
}
});
Let’s insert all 100,000,000
in parallel!!!!

53
What if I have to insert 100M documents?
for (i = 1; i <= 100000000; i++) {
{},
db.close();
});
}
});
FATAL ERROR: CALL_AND_RETRY_LAST Allocation failed - JavaScript heap out of memory

54
for (i = 1; i <= 100000000; i++) {
{},
console.log("Insert C…");
});
}
Callback
Queue
Event Loop

55
for (i = 1; i <= 100000000; i++) {
{},
db.close();
});
Callback
Queue
Event Loop
col.insert()
col.insert()
col.insert()
col.insert()
col.insert()
col.insert()
col.insert()
col.insert()
col.insert()

56
for (i = 1; i <= 100000000; i++) {
{},
db.close();
});
Callback
Queue
Event Loop
col.insert()
col.insert()
col.insert()
col.insert()
col.insert()
col.insert()
col.insert()
col.insert()
col.insert()
FATAL ERROR: CALL_AND_RETRY_LAST Allocation failed - JavaScript heap out of memory

57
Let’s try 5 at a time
var DOCS_TO_INSERT = 1000;
var numInsertsRunning = 0; // number of insert threads
var insertCount = 0; // number of documents inserted so far
for (i = 0; i < 5; i++) {
++numInsertsRunning;
insertDocument(db, col, ++insertCount, i, function (err, result) {
console.log("All ", DOCS_TO_INSERT, " documents inserted.");
db.close();
});
}
});

58
insertDocument function
function insertDocument (db, col, docNum, threadNum, callback) {
col.insert({x: ++insertCount, y: 2, z: 3},
{},
console.log("Thread: ", threadNum, " inserted doc: ", docNum, ".");
if (insertCount < DOCS_TO_INSERT)
insertDocument(db, col, ++insertCount, threadNum, callback);
else if (numInsertsRunning == 1) {
numInsertsRunning--;
callback(null, true);
}
else
numInsertsRunning--;
});
}

59
InsertDocument Callback Logic
col.insert({x: ++insertCount, y: 2, z: 3}, function (err, result) {
}
Have all the documents
been inserted?
Call insertDocument
again
Are other inserts still
running?
Do nothing & decrement
running thread count
All inserts done
Call the original callback
Yes Yes
No No

60
Bulk Inserts
• The previous example was for illustrative purposes
• MongoDB provides a buik write API that provides better performance for bulk writes
• The bulk write API batches up writes
– Batch writes with a single acknowledgement
• Use collection.bulkWrite
• Improve performance using multiple bulkWrite threads
– Previous example will be identical
– Replace collection.insert with collection.bulkWrite

61
Another word of caution
• All my examples established a MongoDB connection and then closed it
– This was for illustrative purposes
• Don’t continuously open and close MongoDB connections.
• Open a connection once once
– Use that connection through the life of the program
– Close it at the end

62
Summary
• Asynchronous vs synchronous programming
• Call stack, event loop, driver API
• Flow control
• Find, insert, update examples
• Managing multiple parallel threads
– bulk insert example
• Learn from my mistakes and misconceptions

Questions?
jay.runkel@mongodb.com
@jayrunkel
Github: https://github.com/jayrunkel/nodeJSWebJun2016

Getting Started with MongoDB and NodeJS

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