MongoDB. CSC309 TA: Sukwon Oh

Transcription

1 MongoDB CSC309 TA: Sukwon Oh

2 Review SQL declarative language for querying data tells what to find and not how to find

3 Review RDBMS Characteristics Easy to use Complicated to use it right Fixed schema Difficult to handle large amount of data Why? How the system works is hidden!

4 Review NoSQL Philosophy (Not-Only SQL) Simpler DB operations Complex query logic is moved to application code Relaxes ACID guarantees for better performance

5 Review Types of NoSQL DB Key-Value Store Key-Data Structure Store Key-Document Store

6 Why MongoDB? To handle big amount of data Better performance Handle failures easily Dynamic schema Don t need complex query operations Your app is already using JSON...

7 Basics

8 Basics

9 Basics Each DB has a set of collections Each collection has a set of documents Document looks like JSON format All documents have _id field with unique values (primary key) Each document contains a set of key-value pairs

10 Sample Document {... address : { building : 1007, coord : [ , ], street : Morris Park Ave,

11 How to use MongoDB? First install MongoDB by following instructions at org/downloads Install node.js MongoDB driver (or any other language you want to use) npm install mongodb

12 Node.js Driver MongoDB API that you can use from express.js Supports CRUD operations CRUD - create, read, update, delete

13 Connecting to DB var client = require( mongodb ).MongoClient; client.connect(url, function(err, db) { console.log( connected! ); db.close(); // closes connection });

14 MongoDB URI Address of MongoDB instance you want to connect [/database][?options] Example mongodb://localhost:27017/test

15 Create insertone(), insertmany() inserts 1 or multiple documents to a collection specified. _id field is automatically generated insertone Syntax: db.collection( collection ).insertone( {//document}, function(err, result){..} );

16 Create insertmany Syntax: db.collection( collection ).insertmany( [{//doc1}, {//doc2},...], function(err, result){..} );

17 Read Use find() to query DB All queries are performed on a single collection Use filters to select only interesting documents Similar to WHERE clause in SQL Returns cursor object, which you can use to iterate over query results Use cursor.each() to look at individual document

18 Filter Filters are in following format {<field1>: <value1>, <field2>: <value2>..} Examples { borough : Manhattan } { addresses.zipcode : } { ratings : [5,8,9]} { ratings.0 : 5}

19 Example var cursor = db.collection( restaurants ).find({ borough : Manhattan }); cursor.each(function(err, doc) { console.log(doc); });

20 Query Operators Filter can be complex by using following operators $or $gt $lt $elemmatch $eq...

21 Query Operators {<field1>: {<operator1>: <value1>}} Examples { grades.score : {$gt: 30}} {ratings: {$elemmatch: {$gt: 5, $lt: 9}}}

22 Query Operators Logical AND Write multiple filters separated by commas Example { cuisine : Italian, address.zipcode : }

23 Query Operators Logical OR Use $or Examples {$or: [ { cuisine : Italian }, { address.zipcode : } ] }

24 Sorting Use.sort() method after.find() Similar to ORDER BY in SQL Accepts a document with keys to sort by and values as 1 for ascending order and -1 or descending order Example { borough : 1, address.zipcode : -1}

25 Cursor methods We have used each() but other methods are available skip(# doc to skip) sort() next() toarray() map()

26 Update updateone(), updatemany(), replaceone() Accepts 3 paramters a filter update value options Cannot update _id field!

27 Update Operators $set to change a field value $currentdate to update a field value to current date...

28 Update updateone/updatemany Syntax: db.collection( collection ).updateone/many( {//filter}, {//update value}, function(err, result) {..} );

29 Example db.collection( restaurants ).updatemany( { address.zipcode : 10016, cuisine: Other }, { $set: {cuisine: Category to be determined }, $currentdate: { lastmodified : true} }, function(err, results) { console.log(results); } );

30 replaceone replaceone() will only preserve field values that are updated and throw away existing fields that are untouched! Same syntax as insertone()

31 More on Update By default, MongoDB does nothing when none of documents are matched. However when upsert option is set to true, it will insert a new document if no matching documents are found.

32 Delete deleteone(), deletemany() Accepts a filter to choose which documents to delete Does not delete indexes or collections Indexes are explained in next tutorial

33 Delete Syntax: db.collection( collection ).deletemany( {//filter}, function(err, result) {..} );

34 Example db.collection( restaurants ).deleteone( { borough : Queens }, function(err, results) { console.log(results); } );

35 Drop To completely remove a collection, consider using drop() Many be more efficient than deletemany({}) Syntax: db.collection( collection ).drop(function(err, results) {..});

36 Aggregation Operates on multiple documents Similar to the popular MapReduce paradigm Perform stage-based aggregation Example Stage 1: Filter out uninteresting documents Stage 2: Group documents by some key Stage 3: Count # of documents with same key

37 Aggregation Syntax: db.collection.aggregate([<stage1>, <stage2>,..])

38 Group Stage Use $group to specify a stage {$group: { _id : $key, field1 : {//accumulator}} Example {$group:{ _id : $borough, count : {$sum: 1}}}

39 Accumulators Only available in group stage and computes values by combining documents with same key $sum $avg $max $min

40 Match Stage Filters documents Uses query syntax from before {$match: {//filter}}

41 Example db.collection( restaurants ).aggregate( [ {$match: { borough : Queens, cuisine : Brazilian }}, {$group: { _id : $address.zipcode, count : {$sum: 1}}} ] ).toarray(function(err, result) { console.log(result); });