Getting the latest documents from a Cloudant/CouchDB database from NodeJS

Question

I would like to take the last n documents from my Cloudant database using a Node query. So far I have narrowed it down to the find() function, but the documentation only really explains how to retrieve all documents containing an absolute value, for example:

db.find({selector:{name:'Alice'}}, function(er, result) {
    ...
});

(taken from https://www.npmjs.com/package/cloudant#cloudant-query)

What I'm looking for is the equivalent of this SQL:

SELECT * FROM db WHERE name = "Alice" LIMIT 10

The code I have so far is this:

var cloudant = require('cloudant');
cloudant({account: username, password: password}, function (err, conn) {
    if (err) {
        callback("Could not initialize connection to Cloudant: " + err);
    } else {
        var db = conn.db.use('mydb');
        db.find(???, function(err, data) {
            if (err) {
                callback("No data found: " + err);
            } else {
                ...
            }
        });
    }
});

If I need to make design documents, I'd do so in the Cloudant online interface, so don't worry too much about making an executable answer for that if it's necessary.

Glynn Bird Glynn Bird · Accepted Answer · 2015-11-26T09:38:23

It's important to note that Cloudant Query requires you to define your index before performing the query e.g. to index the 'name' field from your documents:

db.index( {name:'nameindex', type:'json', index:{fields:['name']}}

We can now query the data using the find function as you indicated:

var query = { selector: { name: 'Alice' }};
db.find(query, function(err, data) {
});

The interesting thing about your question is the phrase 'the last n documents'. We can retrieve 'n' documents by adding a 'limit' to our query.

var query = { selector: { name: 'Alice' }, limit: 10};
db.find(query, function(err, data) {
});

but this doesn't necessarily indicate the last ten documents; it just limits the result set to ten.

If you want your query results to appear in time order, then you'll need something in your documents that indicates the time e.g.

a time string : { "name": "Alice", "datetime": "2015-11-26 10:22:24 Z" }
a timestamp : { "name": "Alice", "ts": "123456678" }

When your document contains a field which represents time, then your index can be created incorporate this into the index e.g.

db.index( {name:'nameindex', type:'json', index:{fields:['name','time']}}

and documents can be queried to appear in *reverse order * (to get the latest first):

var query = { selector: { name: 'Alice' }, sort: [ { name: "desc"}, { ts: "desc"]};
db.find(query, function(err, data) {
});

You may also want to look at type:"text" indexes too. See https://docs.cloudant.com/cloudant_query.html

Getting the latest documents from a Cloudant/CouchDB database from NodeJS

2 Answers