CouchDB count all documents and return a number? - node.js

Question

We have a college project in CouchDB and I'm using node, I want to create a view that returns a number of all my documents by email.
I cannot find anything that works and I'm not sure what I'm missing, I tried a lot of different reduce functions and emit methods.
Thanks for any answers.
The documents have 2 fields, name and email

Answer 1

Do not use the db endpoint because the response field doc_count includes design documents along with other documents that may not have an email field.
A straight forward way to do this is with a view. The code snippet demonstrates the difference between db info doc_count and a view's total_rows using PouchDB. I'd guess there's probably more interesting uses for the index.
The design doc is trivial
{
_id: '_design/my_index',
views: {
email: {
map: function(doc) {
if (doc.email) emit(doc.email);
}.toString()
}
}
}
And the view query is very efficient and simple.
db.query('my_index/email', {
include_docs: false,
limit: 0
})
const gel = id => document.getElementById(id);
let db;
function setJsonToText(elId, json) {
gel(elId).innerText = JSON.stringify(json, undefined, 3);
}
async function view() {
// display db info
setJsonToText('info', await db.info());
// display total number or rows in the email index
const result = await db.query('my_index/email', {
include_docs: false,
limit: 0
});
setJsonToText('view', result);
}
// canned test documents
function getDocsToInstall() {
return [{
email: 'jerry#garcia.com',
},
{
email: 'bob#weir.com',
},
{
email: 'phil#lesh.com'
},
{
email: 'wavy#gravy.com'
},
{
email: 'samson#delilah.com'
},
{
email: 'cosmic#charlie.com'
},
// design doc
{
_id: '_design/my_index',
views: {
email: {
map: function(doc) {
if (doc.email) emit(doc.email);
}.toString()
}
}
}
]
}
// init example db instance
async function initDb() {
db = new PouchDB('test', {
adapter: 'memory'
});
await db.bulkDocs(getDocsToInstall());
};
(async() => {
await initDb();
await view();
})();
<script src="https://github.com/pouchdb/pouchdb/releases/download/7.1.1/pouchdb-7.1.1.min.js"></script>
<script src="https://github.com/pouchdb/pouchdb/releases/download/7.1.1/pouchdb.memory.min.js"></script>
<pre>Info</pre>
<pre id='info'></pre>
<div style='margin-top:2em'></div>
<pre>email view</pre>
<pre id='view'>
</pre>

Answer 2

You can use GET /{db}, which returns information about the specified database. This is a JSON object that contains the property doc_count.
doc_count (number) – A count of the documents in the specified database.
With Angular for example, this could be done with the following method:
async countDocuments(database: string): Promise<number> {
return this.http.get<any>(this.url('GET', database), this.httpOptions).toPromise()
.then(info => info['doc_count']);
}

Answer 3

Assumption:
Assuming that following documents are present in the Customers database:
[
{
"_id": "93512c6c8585ab360dc7f535ff00bdfa",
"_rev": "1-299289ee89275a8618cd9470733035f4",
"name": "Tom",
"email": "tom#domain.com"
},
{
"_id": "93512c6c8585ab360dc7f535ff00c930",
"_rev": "1-a676883d6f1b5bce3b0a9ece92da6964",
"name": "Tom Doe",
"email": "tom#domain.com"
},
{
"_id": "93512c6c8585ab360dc7f535ff00edc0",
"_rev": "1-09b5bf64cfe66af7e1134448e1a328c3",
"name": "John",
"email": "john#domain.com"
},
{
"_id": "93512c6c8585ab360dc7f535ff010988",
"_rev": "1-88e347af11cfd1e40e63920fa5806fd2",
"name": "Alan",
"email": "alan#domain.com"
}
]
If I understand your query correctly, then based on above data, You need below given result set.
{
"tom#domain.com": 2,
"alan#domain.com": 1,
"john#domain.com": 1
}
Solution:
In order to achieve above, Consider following design document containing a View which has Map and Reduce functions.
{
"_id": "_design/Customers",
"views": {
"by-email": {
"map": "function (doc) {
if(doc.email){
emit(doc.email, doc._id);
}
}",
"reduce": "_count"
}
},
"language": "javascript"
}
The above view function emits value of the key email of the document if the key exists in the document.
The reduce function _count is a built in reducer (provided by CouchDB) that does the counting logic.
Executing View Query:
In order to query this view, you need to: select the view function, mark reduce to be executed (as it is optional to run reduce) and set 1 as group level.
Here is how you can do it through the UI:
Result:
Here is the result given by above query:
[![result of map reduce query
Hope this helped.
For more details about other reduce functions and group level, please refer CouchDB documentation.
Cheers.