How to count and do jointure like stuff on couchDB - couchdb

Question

I'm currently trying to get the number of events for one organizer.
This is what my organizer document looks like:
{
"doc_type": "User",
"email": "xxx#gmail.com",
"blebleble: "blebleble",
}
This is what my event document looks like:
{
"doc_type": "Event",
"email": "xxx#gmail.com",
"blablabla: "blablabla",
}
I still couldn't figure out how to do some kind of jointure between both docs and do a count on the number of event that shares the same. I think I can work around the email that both docs shares but I don't know how I can do that. I'm still having trouble with CouchDB. Doesn't seems like a hard thing to do in SQL, but can't find out for nosql.
Thanks you in advance.

Answer 1

"jointure" is not not a term I've encountered in my field so I am left to guess what is meant is join.
Joins are possible with CouchDB views, but what I read from the requirement in the OP is to get counts of events by email. See CouchDB's Joins With Views documentation. For that, I don't see documents with an ancestral relation rather a one-to-many relation, i.e. user ==> events.
Consider this design document:
{
"_id": "_design/SO-68999682",
"views": {
"user_events": {
"map": `function (doc) {
if(doc.doc_type === 'Event') {
emit(doc.email);
}
}`,
"reduce": '_count'
}
}
The view's map function simply adds doc.email to the 'user_events' index when appropriate. Of particular interest the reduce function specifies the built-in reduce function _count.
Given such a view index one may apply the /db/_design/design-doc/_view/view-name endpoint to, for example,
View all events
{
reduce: false,
include_docs: true
}
Get a count of all events
{
reduce: true
}
Get a count of events for every email (summary)
{
reduce: true,
group_level: 1
}
Get a count of events for a specific email
{
reduce: true,
group_level: 1,
key: email
}
Get all events for a specific email
{
reduce: false,
include_docs: true,
key: email
}
The _count reduce built-in provides high performance. The snippet below demonstrates the above using the very handy and compatible PouchDB.
async function showAllEventDocs() {
let result = await db.query('SO-68999682/user_events', {
reduce: false,
include_docs: true
});
//show
gel('user_events_view').innerText = result.rows.map(row => [row.doc.email, row.doc.date].join('\t\t')).join('\n');
}
async function showEventCountTotal() {
let result = await db.query('SO-68999682/user_events', {
reduce: true
});
gel('event_count_total').innerText = result.rows[0].value;
}
async function showEventCountSummary() {
let result = await db.query('SO-68999682/user_events', {
reduce: true,
group_level: 1
});
//show key/value (email, count)
gel('event_count_summary').innerText = result.rows.map(row => [row.key, row.value].join('\t\t')).join('\n');
}
async function showUserEventCount(email, displayElement) {
let result = await db.query('SO-68999682/user_events', {
reduce: true,
group_level: 1,
key: email
});
//show value (count)
gel(displayElement).innerText = result.rows[0].value;
}
async function showUserEvents(email, displayElement) {
let result = await db.query('SO-68999682/user_events', {
reduce: false,
include_docs: true,
key: email
});
//show
gel(displayElement).innerText = result.rows.map(row => [row.doc.email, row.doc.date].join('\t\t')).join('\n');
}
function getDocsToInstall(count) {
const docs = [{
"doc_type": "User",
"email": "Jerry#gmail.com"
},
{
"doc_type": "User",
"email": "Bobby#gmail.com"
},
{
"doc_type": "Event",
"email": "Jerry#gmail.com",
"date": getDocDate().toISOString().slice(0, 10)
}, {
"doc_type": "Event",
"email": "Jerry#gmail.com",
"date": getDocDate().toISOString().slice(0, 10)
}, {
"doc_type": "Event",
"email": "Jerry#gmail.com",
"date": getDocDate().toISOString().slice(0, 10)
}, {
"doc_type": "Event",
"email": "Bobby#gmail.com",
"date": getDocDate().toISOString().slice(0, 10)
}, {
"doc_type": "Event",
"email": "Bobby#gmail.com",
"date": getDocDate().toISOString().slice(0, 10)
},
];
// design document
const ddoc = {
"_id": "_design/SO-68999682",
"views": {
"user_events": {
"map": `function (doc) {
if(doc.doc_type === 'Event') {
emit(doc.email);
}
}`,
"reduce": '_count'
}
}
};
docs.push(ddoc);
return docs;
}
const db = new PouchDB('SO-68999682', {
adapter: 'memory'
});
// install docs and show view in various forms.
(async() => {
await db.bulkDocs(getDocsToInstall(20));
await showAllEventDocs();
await showEventCountTotal();
await showEventCountSummary();
await showUserEventCount('Jerry#gmail.com', 'jerry_event_count');
await showUserEventCount('Bobby#gmail.com', 'bobby_event_count');
await showUserEvents('Jerry#gmail.com', 'jerry_events');
await showUserEvents('Bobby#gmail.com', 'bobby_events');
})();
const gel = id => document.getElementById(id);
function getDocDate() {
const today = new Date();
const day = Math.random() * 100 % today.getDay() + 1; // keep it basic
return new Date(today.getFullYear(), today.getMonth(), day)
}
.bold {
font-weight: bold
}
.plain {
font-weight: normal
}
<script src="https://cdn.jsdelivr.net/npm/pouchdb#7.1.1/dist/pouchdb.min.js"></script>
<script src="https://github.com/pouchdb/pouchdb/releases/download/7.1.1/pouchdb.memory.min.js"></script>
<pre>All user_events (entire view)</pre>
<pre id='user_events_view'></pre>
<hr/>
<pre>Total number of events: <span id='event_count_total'></span> events</pre>
<hr/>
<pre>Event count summary (user, count)</pre>
<pre id='event_count_summary'></pre>
<hr/>
<pre>Event count by email (specific to user)</pre>
<pre>Bobby#gmail.com has <span id='bobby_event_count'></span> events</pre>
<pre>Jerry#gmail.com has <span id='jerry_event_count'></span> events</pre>
<hr/>
<pre>Events by email</pre>
<pre class="bold">Bobby#gmail.com <pre class="plain" id='bobby_events'></pre></pre>
<pre class="bold">Jerry#gmail.com <pre class="plain" id='jerry_events'></pre></pre>
<hr/>
Notice the demo snippet's documents have a date field. If such a field existed in the OPs Event documents, then changing the emit to
emit(doc.email + '/' + doc.date);
would allow all the aforementioned queries plus the option to query by a date or date range, an exercise which I'll leave readers to explore.