CouchDB, PouchDB and Offline-Tolerant Apps

CouchDB, PouchDB and Offline-Tolerant Apps

From Dutch PHP Conference

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Lorna Mitchell

July 01, 2017
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  1. CouchDB, PouchDB and Offline-Tolerant Apps Lorna Mitchell, IBM

  2. NoSQL? @lornajane

  3. @lornajane

  4. @lornajane

  5. Document Databases Store collections of schemaless documents @lornajane

  6. 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
  7. 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
  8. 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
  9. 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
  10. 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
  11. 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
  12. 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
  13. 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
  14. Fauxton Friendly web interface @lornajane

  15. Fauxton @lornajane

  16. Fauxton @lornajane

  17. CouchDB: Lovely Doc DB I could stop here: • JSON

    format • HTTP interface and nice web UI • Scales well • Modern, performant document database @lornajane
  18. Changes Feed A feed containing all database changes. GET /_changes

    @lornajane
  19. Replication @lornajane

  20. 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
  21. 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
  22. 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
  23. Mango (sample data: https://www.ibm.com/communities/analy tics/watson-analytics-blog/sales-products-sample-data/) @lornajane

  24. 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
  25. Mango: CouchDB Queries @lornajane

  26. Mango: Example Query Use a query like this with the

    _find endpoint { "selector": { "Year": {"$eq": "2012"} }, "fields": ["Quarter", "Product line"], "limit": 5 } @lornajane
  27. 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
  28. Mango: Indexes Describe the index in JSON, then use the

    _index endpoint { "index": { "fields": ["Year"] }, "name": "Year" } @lornajane
  29. 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
  30. Views @lornajane

  31. 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
  32. 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
  33. MapReduce Primer: Map @lornajane

  34. MapReduce Primer: Map @lornajane

  35. MapReduce Primer: Map @lornajane

  36. MapReduce Primer: Map @lornajane

  37. MapReduce Primer: Reduce @lornajane

  38. 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
  39. Views Example @lornajane

  40. CouchDB Sync Enables OfflineFirst Apps @lornajane

  41. 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
  42. PouchDB @lornajane

  43. PouchDB in Action In index.html: <script src="/js/pouchdb-6.1.2.min.js"></script> <script src="/js/shopping.js"></script> shopping.js

    is where my client-side JavaScript lives Code is here: https://github.com/lornajane/robust-shopping-list @lornajane
  44. 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
  45. PouchDB in Action OfflineFirst for robust web applications @lornajane

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

  47. 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
  48. Emergency Backup Slides @lornajane