Node js mongodriver

An introduction to the
node.js mongo driver
Christian Amor Kvalheim

• Asynchronous Javascript platform built on
top of V8
• Single-threaded
• Package manager
• Awesome

Hello World Server
var http = require('http');

http.createServer(
function (req, res) {
res.writeHead(200,
{'Content-Type': 'text/plain'});
res.end('Hello Worldn');
}).listen(8124, "127.0.0.1");

Hello World Server
Load the http library

http.createServer(
res.writeHead(200,
}).listen(8124, "127.0.0.1");

Hello World Server
Load the http library
Set up the connection
http.createServer( handler
res.writeHead(200,
}).listen(8124, "127.0.0.1");

How to get started

• Install node.js (from source or package)
• Install npm (node package manager)
• Create an empty directory
• npm install mongodb
• npm install express

Let’s do some code

• Using Express and Mongo
• Textmate basic.js

Picking it apart
var db = new Db('node-mongo-examples', new Server(host, port, {}),
{native_parser:false});

db.open(function(err, db) { ...
.....
app.listen(8124);

var app = express.createServer();

app.get('/', function(req, res){
res.send('Hello World');
});

Picking it apart
Creates a db using the js bson parser

.....
app.listen(8124);


});

Picking it apart

Opens the connection to the db
.....
app.listen(8124);


});

Picking it apart

Opens the connection to the db
.....
app.listen(8124);

The server is now running with access to
the mongo server connection

});

Let’s add some meat

• CRUD operations
• Textmate basic_2.js

Picking it apart
// Create method
app.post('/location', function(req, res) {
geoCodeDecorateObject(req.body.address, {description:req.body.description},
function(err, object) {
db.collection('locations', function(err, collection) {

// Insert doc
collection.insert(object, {safe:true}, function(err, result) {

// Fetch all docs for rendering of list
collection.find({}).toArray(function(err, items) {
res.render('./basic_2.jade', {locals: {locations:items}});
})
});
});
});
});

Picking it apart
Geo Encode Address
// Create method

// Insert doc

})
});
});
});
});

Picking it apart
Geo Encode Address
// Create method

// Insert doc

})

Insert record, safe ensures that we trap any
});
});
});
errors by doing a error check against
});

mongodb

Picking it apart
// Create method

// Insert doc

})
});
});
});
ﬁnd all records from the locations
});

collection. Find returns a cursor that allows
for stepping through doucments

Safe or not

• Mongo Insert/Update/Delete are async
• 2nd call to lastError required to check for
the success of the operation
• safe option ensures the second error call
• you can also run the driver in strict mode


• CRUD operations

Picking it apart
// Delete method
app.del('/location', function(req, res) {
var id = ObjectID.createFromHexString(req.body.id);
collection.remove({_id:id}, {safe:true}, function(err, numberOfDeletedRecords) {

})
})
});
});

Picking it apart
Convert hex string to
// Delete method objectID

})
})
});
});

Picking it apart
// Delete method objectID


})
})
Remove the document using the speciﬁc id
});
});
passed in, using safe.


• CRUD operations

Picking it apart
// Get method
app.get('/location', function(req, res) {

collection.findOne({_id:id}, function(err, item) {

res.render('./basic_4.jade', {locals: {locations:items, location:item}});
})
})
});
});

Picking it apart
// Get method
objectID


})
})
});
});

Picking it apart
// Get method
objectID



})
})
Locate one document by id
});
});


• CRUD operations

Picking it apart
// Update method
app.put('/location', function(req, res) {

collection.findOne({_id:id}, function(err, object) {
object.description = req.body.description;
object.address = req.body.address;

geoCodeDecorateObject(req.body.address, object, function(err, object) {

collection.update({_id:object._id}, object, {safe:true}, function(err,
numberOfUpdatedObjects) {

})
})
})

Picking it apart
// Update method
Locate object we wish
to modify




})
})
})

Picking it apart
// Update method
Locate object we wish
to modify




})

})
}) Update document using the id to select
what document to update


• Final with search

Picking it apart
db.open(function(err, db) {
if(err) throw err

// !!! CHANGE
db.ensureIndex("locations", {loc:"2d"}, function(err, result) {
if(err) throw err

app.listen(8124);
})
});

Picking it apart
db.open(function(err, db) {
if(err) throw err

// !!! CHANGE
db.ensureIndex("locations", {loc:"2d"}, function(err, result) {
if(err) throw err

app.listen(8124);
})
}); Ensures there is a 2d geospatial index on
the attribute loc on any document in the
locations collection

Picking it apart
var geoCodeDecorateObject = function(address, object, callback) {
var googleGeoCodeApi = {host: 'maps.googleapis.com',
port: 80,path: '/maps/api/geocode/json?sensor=false&address=' +
escape(address),
method: 'GET' };

var clientReq = http.get(googleGeoCodeApi, function(clientRes) {
var data = [];
clientRes.on('data', function(chunk) {
data.push(chunk.toString());
});
clientRes.on('end', function() {
var googleObject = JSON.parse(data.join(''));

object.address = address;
object.geodata = googleObject.results.pop();

// !!! CHANGE
object.loc = {long:object.geodata.geometry.location.lng,
lat:object.geodata.geometry.location.lat};

callback(null, object);
});

Picking it apart
var geoCodeDecorateObject = function(address, object, callback) {
var googleGeoCodeApi = {host: 'maps.googleapis.com',
port: 80,path: '/maps/api/geocode/json?sensor=false&address=' +
escape(address),
method: 'GET' };

var clientReq = http.get(googleGeoCodeApi, function(clientRes) {
var data = [];
clientRes.on('data', function(chunk) {
data.push(chunk.toString());
We are adding a loc
});
clientRes.on('end', function() {
attribute to all
var googleObject = JSON.parse(data.join(''));
documents with
object.address = address;
object.geodata = googleObject.results.pop(); longtidude and
// !!! CHANGE latitude in the right
object.loc = {long:object.geodata.geometry.location.lng,
lat:object.geodata.geometry.location.lat}; order for mongodb to
callback(null, object);
});
search

Picking it apart
// !!! CHANGE
// Search option
app.post('/search', function(req, res) {
geoCodeDecorateObject(req.body.address, {}, function(err, object) {
// Unpack geo object
var long = object.geodata.geometry.location.lng;
var lat = object.geodata.geometry.location.lat

collection.find({loc : {'$near': [long, lat], '$maxDistance':
parseFloat(req.body.distance)}}).toArray(function(err, geoItems) {
res.render('./basic_6.jade', {locals: {locations:items,
results:geoItems}});
})
});
});
});
});

Picking it apart
Encode address for
// !!! CHANGE
// Search option searching

})
});
});
});
});

Picking it apart
Encode address for
// !!! CHANGE
// Search option searching

})
});
Search for all items $near our address at
});
});
$maxDistance
});

Other features

• Cursors
• Grid FS

Cursors

• toArray Function
• each Function
• streamRecords Function

toArray

collection.find().toArray(function(err, documents){
test.deepEqual([1, 2, 3], documents[0].b);
// Let's close the db
test.done();
});

toArray
Fetches all docs in one go
for the query. Use with
caution
collection.find().toArray(function(err, documents){
test.deepEqual([1, 2, 3], documents[0].b);
// Let's close the db
test.done();
});

each

collection.find({}, {'sort':[['age', 1]]}).each(function(err, item){
if(item != null) {
// Do work
} else {
// Finished
}
});

each
Fetches docs in batches and
allows iteration over results

if(item != null) {
// Do work
} else {
// Finished
}
});

each
Fetches docs in batches and
allows iteration over results

if(item != null) {
// Do work
} else {
// Finished
}
});
Returns null when no more
results available

streamRecords
var stream = collection.find({}, {'limit' :
3}).streamRecords();

stream.on('end', function() {
// No more results in the pipe
});

stream.on('data',function(data){
// Item
});

streamRecords

stream.on('end', function() {
});

// Item
});

When an item is ready the
event ‘data’ is triggered

streamRecords
When no more items
stream.on('end', function() { are available
});

// Item
});


streamRecords
When no more items
stream.on('end', function() { are available
});

REFERED
P
// Item
});


Grid FS

• Write and read a ﬁle
• Stream a ﬁle

Write a ﬁle
var gridStore = new GridStore(client, 'test_gs_writing_file', 'w');

gridStore.open(function(err, gridStore) {

gridStore.writeFile('./test_gs_weird_bug.png', function(err, gridStore) {

GridStore.read(client, 'test_gs_writing_file', function(err, fileData) {
});

Write a ﬁle



Writes the ﬁle in chunks to
mongodb (avoids freezing the
eventloop in node.js)

});

Write a file



Writes the file in chunks to
mongodb (avoids freezing the
eventloop in node.js)

});

Read the whole file. Careful with the
memory

Stream a ﬁle
var gridStore = new GridStore(client, "test_gs_read_stream", "r");

gridStore.open(function(err, gs) {
var stream = gs.stream(true);

stream.on("data", function(chunk) {
// Received a chunk of data
});

stream.on("end", function() {
// Finished streaming
});
});

Stream a ﬁle


Receive a chunk and do something
});

});
});

Stream a ﬁle


});
Finshed stream the ﬁle

});
});

Stream a ﬁle


});
Finshed stream the ﬁle

// Finished streaming PR EFE RED
});
});

Typical starting problems
for(var i = 0; i < 100; i++) {
collection.insert({'i':i});
}

collection.count(function(err, count) {
// count is > 0 <= 100
});

for(var i = 0; i < 100; i++) {
}

All executed in parallel, non-
deterministic end of execution
// count is > 0 <= 100
});

for(var i = 0; i < 100; i++) {
}

All executed in parallel, non-
deterministic end of execution
// count is > 0 <= 100
});

All inserts MAY have been written
to disk so passes most of the time.
But with Pooling NO WAY

for(var i = 0; i < 100; i++) {
collection.insert({'i':i}, {safe:true}, function(err, result) {
// Do something
});
}

??????????????????????????????
// count is > 0 <= 100
});

for(var i = 0; i < 100; i++) {
// Do something
});
} How do we handle the callbacks
??????????????????????????????
// count is > 0 <= 100
});

for(var i = 0; i < 100; i++) {
// Do something
});
??????????????????????????????
// count is > 0 <= 100
});

How do we get to this code ??????

for(var i = 0; i < 100; i++) {
// Do something
});
??????????????????????????????
// count is > 0 <= 100
});

How do we get to this code ??????

Many possible solutions

My Choosen Solution
https://github.com/creationix/step
Step(
function insert() {
var group = this.group();
for(var i = 0; i < 100; i++) {
collection.insert({'i':i}, {safe:true}, group());
}
},

function finished() {
// Count is 100 :)
});
}
)

My Choosen Solution
Step(
function insert() {
for(var i = 0; i < 100; i++) {
}
}, Ensures all the inserts are ﬁnished
before calling the next function
// Count is 100 :)
});
}
)

My Choosen Solution
Step(
function insert() {
for(var i = 0; i < 100; i++) {
}
}, Ensures all the inserts are ﬁnished
before calling the next function
// Count is 100 :)
});
}
) When all inserts are done :)

DONE
Code on
https://github.com/christkv/mongodb-hamburg

Node js mongodriver

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