CouchDB uses MapReduce as a tool to let you introspect your data and build persistent indices for fast query responses, incrementally.

1. Lab: Map/Reduce Views (30 minutes)
Bradley Holt, Developer Advocate
Thursday, February 9, 2017
CouchDB Developer Day
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2. Prerequisite: Replication Lab
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4. Key Concepts
 Design documents
 Views
 Map functions
 Reduce functions
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5. http-console
$ npm install http-console -g
@BradleyHolthttps://github.com/cloudhead/http-console

6. http-console
$ npm install http-console -g
$ http-console 127.0.0.1:5984
@BradleyHolthttps://github.com/cloudhead/http-console

7. http-console
$ npm install http-console -g
$ http-console 127.0.0.1:5984
> http-console 0.6.3
> Welcome, enter .help if you're lost.
> Connecting to 127.0.0.1 on port 5984.
@BradleyHolthttps://github.com/cloudhead/http-console

8. Connecting to CouchDB 2.0
$ http-console root:passw0rd@127.0.0.1:5984 --json
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9. Connecting to CouchDB 2.0
$ http-console root:passw0rd@127.0.0.1:5984 --json
> http-console 0.6.3
> Welcome, enter .help if you're lost.
> Connecting to 127.0.0.1 on port 5984.
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10. Connecting to IBM Cloudant
$ http-console https://bradley-holt:passw0rd@bradley-holt.cloudant.com --json
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11. Connecting to IBM Cloudant
$ http-console https://bradley-holt:passw0rd@bradley-holt.cloudant.com --json
> http-console 0.6.3
> Welcome, enter .help if you're lost.
> Connecting to bradley-holt.cloudant.com on port 443.
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12. Create a Design Document
/>
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13. Create a Design Document
/> /kittens
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14. Create a Design Document
/kittens>
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15. Create a Design Document
/kittens> PUT /_design/kittens
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16. Create a Design Document
/kittens> PUT /_design/kittens
... { "views": { "by_age": { "map": "function(doc) { emit(doc.age_weeks) }" } } }
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17. Create a Design Document
/kittens> PUT /_design/kittens
... { "views": { "by_age": { "map": "function(doc) { emit(doc.age_weeks) }" } } }
HTTP/1.1 201 Created
Content-Type: application/json
{
ok: true,
id: '_design/kittens',
rev: '1-c38a0039638b950f64e02c51fe2e9229'
}
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18. Get the Design Document
/kittens>
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19. Get the Design Document
/kittens> GET /_design/kittens
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20. Get the Design Document
/kittens> GET /_design/kittens
HTTP/1.1 200 OK
Content-Type: application/json
{
_id: '_design/kittens',
_rev: '1-c38a0039638b950f64e02c51fe2e9229',
views: {
by_age: { map: 'function(doc) { emit(doc.age_weeks) }' }
}
}
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21. Query a View
/kittens>
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22. Query a View
/kittens> GET /_design/kittens/_view/by_age
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23. Query a View
/kittens> GET /_design/kittens/_view/by_age
HTTP/1.1 200 OK
Content-Type: application/json
{
total_rows: 5,
offset: 0,
rows: [
{ id: 'smokey', key: 3, value: null },
{ id: 'tiger', key: 7, value: null },
{ id: 'daisy', key: 9, value: null },
{ id: 'mittens', key: 10, value: null },
{ id: 'lily', key: 16, value: null }
]
}
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24. Query a View with Start Key and End Key
/kittens>
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25. Query a View with Start Key and End Key
/kittens> GET /_design/kittens/_view/by_age?startkey=7&endkey=10
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26. Query a View with Start Key and End Key
/kittens> GET /_design/kittens/_view/by_age?startkey=7&endkey=10
HTTP/1.1 200 OK
Content-Type: application/json
{
total_rows: 5,
offset: 1,
rows: [
{ id: 'tiger', key: 7, value: null },
{ id: 'daisy', key: 9, value: null },
{ id: 'mittens', key: 10, value: null }
]
}
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27. Add a Reduce Function
/kittens>
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28. Add a Reduce Function
/kittens> GET /_design/kittens
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29. Add a Reduce Function
/kittens> GET /_design/kittens
HTTP/1.1 200 OK
Content-Type: application/json
{
_id: '_design/kittens',
_rev: '1-c38a0039638b950f64e02c51fe2e9229',
views: {
by_age: { map: 'function(doc) { emit(doc.age_weeks) }' }
}
}
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30. Add a Reduce Function
/kittens>
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31. Add a Reduce Function
/kittens> PUT /_design/kittens?rev=1-c38a0039638b950f64e02c51fe2e9229
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32. Add a Reduce Function
/kittens> PUT /_design/kittens?rev=1-c38a0039638b950f64e02c51fe2e9229
... { "views": { "by_age": { "map": "function(doc) { emit(doc.age_weeks, doc.weight_kilograms) }", "reduce":
"_stats" } } }
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33. Add a Reduce Function
/kittens> PUT /_design/kittens?rev=1-c38a0039638b950f64e02c51fe2e9229
... { "views": { "by_age": { "map": "function(doc) { emit(doc.age_weeks, doc.weight_kilograms) }", "reduce":
"_stats" } } }
HTTP/1.1 201 Created
Content-Type: application/json
{
ok: true,
id: '_design/kittens',
rev: '2-a64e3539068221e7b4eaa94917faed5f'
}
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34. Query a View with a Reduce Function
/kittens>
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35. Query a View with a Reduce Function
/kittens> GET /_design/kittens/_view/by_age
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36. Query a View with a Reduce Function
/kittens> GET /_design/kittens/_view/by_age
HTTP/1.1 200 OK
Content-Type: application/json
{
rows: [
{
key: null,
value: {
sum: 4.8919999999999995,
count: 5,
min: 0.403,
max: 1.95,
sumsqr: 6.15185
}
}
]
}
@BradleyHolt

37. Try It On Your Own
1. Create an view of kittens by weight_kilograms, using age_weeks as the value and
using a _stats reduce function
2. Find kittens weighing less than 1 kilogram (use the reduce=false parameter)
3. Find the stats of kittens weighing less than 1 kilogram
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38. Lab: Map/Reduce Views
CouchDB Developer Day
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