Extend query function to support multiple search criteria in CouchDB/PouchDB - mapreduce

Question

I'm trying to get a count of docs having level: 2, completed: true. However, I'm having trouble wrapping my head around introducing another criteria in the query function. Currently, as evident from the code; it is just printing out docs having completed: true. How can I extend this query to support another query parameter like level too?
[{
_id: 1,
name: 'Test_01',
level: 1,
completed: false
},
{
_id: 2,
name: 'Test_02',
level: 2,
completed: true
},
{
_id: 3,
name: 'Test_01',
level: 3,
completed: false
}]
const myMapReduceFun = {
map: (doc) => {
emit(doc.completed);
}.toString(),
reduce: '_count'
};
db.query(myMapReduceFun, {
key: true, reduce: true
})
.then((result) => {
console.log(result)
})

Answer 1

This is easily done with map/reduce. One strategy is to use complex keys, the other using clever demarcations in a string.
I prefer complex keys as it does not require having to assemble the key or other string based monkey business.
Consider the design document in the demo:
{
_id: "_design/my_index",
views: {
completed_str: {
map: `function (doc) {
emit(doc.completed + '/' + doc.level + '/')
}`,
},
completed_complex: {
map: `function (doc) {
emit([doc.completed,doc.level])
}`,
},
},
}
completed_str uses concatenation and a '/' to create two fields for completed and level
completed_complex uses an array to create a complex key
In the snippet below I've included an example of both approaches. The key (no pun intended) is to emit the 'completed' field first, then the 'level' field.
When toying with the queries, do note the difference in the value Key field returned by the view.
const gel = id => document.getElementById(id);
const g_view_result = 'view_result';
function getQuery() {
let view = gel('view').value;
let completed = gel('completed').value === 'true';
let level = parseInt(gel('level').value, 10);
if (view === 'complex') {
// use complex key view
return {
view: "my_index/completed_complex",
params: {
reduce: false,
include_docs: false,
start_key: [completed, level],
end_key: [completed, level],
}
}
}
// use simple string view
return {
view: "my_index/completed_str",
params: {
reduce: false,
include_docs: false,
start_key: [completed, level, ''].join('/'),
end_key: [completed, level, ''].join('/'),
}
}
}
async function query() {
try {
let html = [];
const view_result = gel(g_view_result);
view_result.innerText = '';
let query = getQuery();
let docs = await db.query(query.view, query.params);
html.push(['ID', 'Key'].join('\t'));
html.push(['----', '--------'].join('\t'));
docs.rows.forEach(row => {
html.push([row.id, row.key].join('\t'));
})
view_result.innerText = html.join('\n');
} catch (e) {
console.log('err: ' + e);
}
}
// canned test documents
function getDocsToInstall() {
return [{
_id: "1",
name: 'Test_01',
level: 1,
completed: false
},
{
_id: "2",
name: 'Test_02',
level: 2,
completed: true
},
{
_id: "3",
name: 'Test_01',
level: 3,
completed: false
},
{
_id: "4",
name: 'Test_4',
level: 3,
completed: true
},
{
_id: "5",
name: 'Test_05',
level: 2,
completed: true
},
{
"_id": "_design/my_index",
"views": {
"completed_str": {
"map": `function (doc) {
emit(doc.completed + '/' + doc.level + '/')
}`
},
"completed_complex": {
"map": `function (doc) {
emit([doc.completed,doc.level])
}`
}
}
}
]
}
let db;
async function initDb() {
db = new PouchDB('test', {
adapter: 'memory'
});
return db.bulkDocs(getDocsToInstall());
}
(async() => {
try {
await initDb();
} catch (e) {
console.log(e);
}
})();
<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>
<label for="completed">Completed:</label>
<select name="completed" id="completed">
<option value="true">True</option>
<option value="false">False</option>
</select>
<label for="level">Level:</label>
<select name="level" id="level">
<option value="0">0</option>
<option value="1">1</option>
<option value="2" selected>2</option>
<option value="3">3</option>
</select>
<label for="view">View:</label>
<select name="view" id="view">
<option value="complex">Complex Key</option>
<option value="simple">Simple String Key</option>
</select>
<button id="query" onclick="query()">Query</button>
<div style='margin-top:2em'></div>
<pre id='view_result'>
</pre>