Cloudant change notifications - couchdb

Question

I am new to Cloudant but have found it useful for a first stage of IoT data. But I need to subscribe to changes based on an id field that is separate from the _id and is unique to the sensor that is sending the data. The examples that I’ve seen so far haven’t helped with this problem. What I’m doing now is sending a separate json doc for each post, so it should return new docs with this sensor id. The json docs sometimes come in by the second but it can be hours as well.
I’m using c# in a .Net web app. The code below creates a call to the Cloudant database and returns the data that I want based on an index that was created for the field SensorID,
json =
{{
"selector": {
"SensorID" : "h7365cf3-17bc-4422-b436-f7bcf12b2e2a"
},
"fields": [
"Data"
]
}}
url = My Cloudant url + ” /_find”.
This returns all docs with the sensorID field that corresponds to the SensorID value in the json query, but just the json object of each doc nested in the Data field.
using (WebClient client = new WebClient())
{
byte[] postBytes = System.Text.ASCIIEncoding.UTF8.GetBytes(json.ToString());
client.UseDefaultCredentials = true;
client.Credentials = new NetworkCredential(username, password);
client.Headers[HttpRequestHeader.ContentType] = "application/json";
var response = client.UploadData(url, "POST", postBytes);
JObject iJson = JObject.Parse(client.Encoding.GetString(response));
return parseIncoming(iJson);
}
When the call is to My Cloudant url + “GET /_DB_UPDATES”, it returns information regarding changes to the whole database. This can be set up as a continuous feed.
I was hoping that this meant that i could subscribe to changes in documents to get new data coming, like Redis Pub/Sub. I’m starting to think that this might not be the case, but if anybody can show me how to do it I would be grateful.

Answer 1

As #adasilva70 said, you need to use the _changes feed.
You can filter changes with an appropriate filter function (so that only changes regarding the documents you're interested in show up).
You can get all updates since a given sequence point (everything since the last data you got) and/or you can use long polling or continuous mode for instant notifications.