CouchDB, PouchDB and Offline-Tolerant Apps Lorna Mitchell, IBM

NoSQL? @lornajane

@lornajane

@lornajane

Document Databases Store collections of schemaless documents @lornajane

CouchDB Cluster Of Unreliable Commodity Hardware • HTTP API • JSON data format • MapReduce views in JavaScript • Mango is JSON-format also CouchDB 2.0 has clustering and sharding features @lornajane

CouchDB HTTP API Hello, CouchDB ~ $ curl http://localhost:5984 {"couchdb":"Welcome","version":"2.0.0", "vendor":{"name":"The Apache Software Foundation"}} List databases ~ $ curl http://localhost:5984/_all_dbs [] @lornajane

CouchDB HTTP API New database ~ $ curl -X PUT http://localhost:5984/shopping {"ok":true} List databases again ~ $ curl http://localhost:5984/_all_dbs ["shopping"] @lornajane

Curl and Not-Curl • love curl? (https://curl.haxx.se/) • try jq (https://stedolan.github.io/jq/) • hate curl? Try one of these • http-console https://github.com/cloudhead/http-console • HTTPie https://httpie.org/ • Postman https://www.getpostman.com/ @lornajane

Try http-console Connect: $ http-console http://localhost:5984 Set database in path (to avoid typing it lots): http://localhost:5984> /shopping Set JSON header: http://localhost:5984/shopping> Content-Type: application/json @lornajane

Try http-console Create item: http://localhost:5984/shopping> PUT /hat ... {"colour": "white"} HTTP/1.1 201 Created Location: http://localhost/shopping/hat Etag: "1-12cb52ad7565b6248c4dbe09f1377e2b" { ok: true, id: 'hat', rev: '1-12cb52ad7565b6248c4dbe09f1377e2b' } @lornajane

Try http-console Update item: http://localhost:5984/shopping> PUT /hat ... {"colour": "blue"} HTTP/1.1 409 Conflict { error: 'conflict', reason: 'Document update conflict.' } To update, include the revision ... @lornajane

Try http-console Update item: http://localhost:5984/shopping> PUT /hat ... {"_rev": "1-12cb52ad7565b6248c4dbe09f1377e2b", "colour": "blue HTTP/1.1 201 Created Location: http://localhost/shopping/hat Etag: "2-15b01d3c5cd2ed475e6ce4cf84b51990" { ok: true, id: 'hat', rev: '2-15b01d3c5cd2ed475e6ce4cf84b51990' } @lornajane

Fauxton Friendly web interface @lornajane

Fauxton @lornajane

Fauxton @lornajane

CouchDB: Lovely Doc DB I could stop here: • JSON format • HTTP interface and nice web UI • Scales well • Modern, performant document database @lornajane

Changes Feed A feed containing all database changes. GET /_changes @lornajane

Replication @lornajane

Replication • Replication can be in either direction - or both • Can be one-off, or continuous • Other CouchDB-compatible storage also exists • e.g. PouchDB, a JavaScript implementation @lornajane

Conflicts Change docs in both places, replicate again: 87bf-bluemix.cloudant.com:443/shopping> GET /hat?conflicts=true { _id: 'hat', _rev: '4-ecbc38075f9a8535c123e523519613b9', colour: 'green', in_stock: 1, _conflicts: [ '3-0bb689d59034fb769d99dcf697ae2de7' ] } CouchDB will always choose the same "winning" doc @lornajane

Conflicts Fetch the "losing" doc(s) with ?rev= parameter 87bf-bluemix.cloudant.com:443/shopping> GET /hat?rev=3-0bb689d5903 { _id: 'hat', _rev: '3-0bb689d59034fb769d99dcf697ae2de7', colour: 'blue', size: 'L' } CouchDB doesn't store old revisions forever @lornajane

Mango (sample data: https://www.ibm.com/communities/analy tics/watson-analytics-blog/sales-products-sample-data/) @lornajane

Mango: CouchDB Queries Mango is a mongo-like query language, useful for ad-hoc querying It is a JSON structure containing: • Selector: the criteria to match records on • Fields: which fields to return • Sort: what order you'd like that in (use with Skip) • Limit: how many records (default = 25) @lornajane

Mango: CouchDB Queries @lornajane

Mango: Example Query Use a query like this with the _find endpoint { "selector": { "Year": {"$eq": "2012"} }, "fields": ["Quarter", "Product line"], "limit": 5 } @lornajane

Mango: Example Query $ curl -X POST -H Content-Type:application/json \ http://localhost:5984/products/_find --data @mango.json {"warning":"no matching index found, create an index to optimize q "docs":[ {"Quarter":"Q1 2012","Product line":"Mountaineering Equipment"}, {"Quarter":"Q1 2012","Product line":"Mountaineering Equipment"}, {"Quarter":"Q1 2012","Product line":"Mountaineering Equipment"}, {"Quarter":"Q1 2012","Product line":"Mountaineering Equipment"}, {"Quarter":"Q1 2012","Product line":"Mountaineering Equipment"} ]} @lornajane

Mango: Indexes Describe the index in JSON, then use the _index endpoint { "index": { "fields": ["Year"] }, "name": "Year" } @lornajane

Mango: Indexes $ curl -X POST -H Content-Type:application/json \ http://localhost:5984/products/_index --data @index.json { "result": "created", "id": "_design/e9b54f2ac34b8823ccbe8aaf6f406d464f50f521", "name": "Year" } Check which indexes are used by putting _explain where the _find normally goes! @lornajane

Views @lornajane

Views • Written in Javascript • Use MapReduce • The map results are stored • Can be used either for filtering, or for aggregation • Geospatial features also available (not in today's talk, sorry) @lornajane

MapReduce Primer: Map • Examine each document, "emit" 0+ keys/value pairs • Scales well because each document is independent • To filter a collection of documents, use map step only @lornajane

MapReduce Primer: Map @lornajane

MapReduce Primer: Map @lornajane

MapReduce Primer: Map @lornajane

MapReduce Primer: Map @lornajane

MapReduce Primer: Reduce @lornajane

MapReduce Primer: Reduce • "Reduce" values in batches with the same key • CouchDB has useful built in functions for most things • Use reduce step when you want aggregate data • (SQL equivalent: a query with GROUP BY) @lornajane

Views Example @lornajane

CouchDB Sync Enables OfflineFirst Apps @lornajane

PouchDB • https://pouchdb.com/ • A database that your client-side javascript can use • Can also sync to CouchDB (-compatible) databases • https://tinyurl.com/fauxton-pouchdb • UI for PouchDB in your browser @lornajane

PouchDB @lornajane

PouchDB in Action In index.html: shopping.js is where my client-side JavaScript lives Code is here: https://github.com/lornajane/robust-shopping-list @lornajane

PouchDB: Replication var db = new PouchDB('shopping'); var remoteDB = new PouchDB('http://localhost:5984/shopping'); window.onload = function() { db.sync(remoteDB, { live: true, retry: true } ).on('change', function (change) { return getItemList().then(function (contents) { document.getElementById('itemList').innerHTML = conten }) }).on('active', function (info) { return getItemList().then(function (contents) { document.getElementById('itemList').innerHTML = conten }); }); @lornajane

PouchDB in Action OfflineFirst for robust web applications @lornajane

CouchDB: Scalable NoSQL Document database: and so much more @lornajane

Questions? Feedback please! https://joind.in/talk/0746b Resources: • https://lornajane.net • https://couchdb.apache.org/ • https://pouchdb.com/ • https://offlinefirst.org If you liked it, tweet: @CouchDB, @PouchDB @lornajane

Emergency Backup Slides @lornajane