I am working with NodeJS and Cloudant (alternatively the DashDB Warehouse if that works better). I wonder if it is possible to have a function in NodeJS that gets called each time a document has been added to the database? I have checked out indexed views but can't really understand how to do it. Does anyone have any good tips regarding this or what documentation to look at?
You can listen to DB _changes in Cloudant (https://console.bluemix.net/docs/services/Cloudant/api/database.html) in continous mode.
Every document change in the Cloudant DB (create,update,delete) will be notified through this channel.
There are different nodejs libraries you can use with this purpose. This is
one example: https://www.npmjs.com/package/cloudant-follow
Related
I have an nodejs server running witch show data on a web interface. The data is fetched from a MongoDB using mongoose. The data is added via an node-red application witch is isolated from the rest.
Currently my nodejs server fetches the data every 5 seconds. Is there a way to know if the data in my MongoDB has changed?
Thanks, I hope my question is clear.
I was also looking for something similar to what you are asking for few months back. Few ways which i know to do it are:
1) You can try to use middlewares while inserting your documents in DB. You can then send that new data either after saving it in DB or at the time of insertion only.
2) Refer to this answer which talks about solving your problem using inbuilt functions provided by mongoDb. You can study in deep about them in mongoDb docs.
3) There is also another way to do this which includes listening to changes in log files. As you know everything done in mongo is recorded and logged in files so whenever there is some change in data you can know it from there also. You will have to do the digging by yourself in this method.
Hope it helps!
We've got an application in Django running against a PGSQL database. One of the functions we've grown to support is real-time messaging to our UI when data is updated in the backend DB.
So... for example we show the contents of a customer table in our UI, as records are added/removed/updated from the backend customer DB table we echo those updates to our UI in real-time via some redis/socket.io/node.js magic.
Currently we've rolled our own solution for this entire thing using overloaded save() methods on the Django table models. That actually works pretty well for our current functions but as tables continue to grow into GB's of data, it is starting to slow down on some larger tables as our engine digs through the current 'subscribed' UI's and messages out appropriately which updates are needed as which clients.
Curious what other options might exist here. I believe MongoDB and other no-sql type engines support some constructs like this out of the box but I'm not finding an exact hit when Googling for better solutions.
Currently we've rolled our own solution for this entire thing using
overloaded save() methods on the Django table models.
Instead of working on the app level you might want to work on the lower, database level.
Add a PostgreSQL trigger after row insertion, and use pg_notify to notify external apps of the change.
Then in NodeJS:
var PGPubsub = require('pg-pubsub');
var pubsubInstance = new PGPubsub('postgres://username#localhost/tablename');
pubsubInstance.addChannel('channelName', function (channelPayload) {
// Handle the notification and its payload
// If the payload was JSON it has already been parsed for you
});
See that and that.
And you will be able to to the same in Python https://pypi.python.org/pypi/pgpubsub/0.0.2.
Finally, you might want to use data-partitioning in PostgreSQL. Long story short, PostgreSQL has already everything you need :)
I'm searching for a framework capable of subscribing to live updates on a paginated list.
The server should take into account the users query for that subscription, and should only send the updates to the subscribers that passes the query instead of broadcasting to everyone.
Is this possible to implement in deepstream.io, and how hard and efficient is it?
I've been using Meteor for this, but I'm trying to deviate from this stack.
Thanks.
Using deepstream in conjunction with RethinkDb should do the trick. Have a look at the official RethinkDb search provider (https://github.com/hoxton-one/deepstream.io-provider-search-rethinkdb) which already creates dynamic lists based on queries. Adding pagination to it should be reasonably straight forward.
I am learning PouchDB with CouchDB and trying to wrap my head around intercepting documents to the couchdb server and performing an action on it wether it be creating other documents, updating the user table, etc.
On the server the json document will be treated through a business layer before it is submitted to the couchdb server, preferably in .net.
Is this possible? If not, is there a way to do so?
Thanks!
On the server side, you can listen to the _changes feed from CouchDB (docs here) and react whenever a document is added, modified, or deleted. This could be useful for reporting/messaging/aggregation/etc.
Alternatively, if you want to do some schema validation on the documents before they are accepted, then you should look into adding a design doc with a validate_doc_update field (docs here).
I am using pouchdb on client side and couchdb on server side. and both are in sync.
I am accessing couchdb from java using client-api lightpouch.
I am storing transaction data, each transaction is stored as document by prefixed _id like
Transaction_1,
Transaction_2
..
..
so on
Now i want to access all the documents where the _id field starts with Transaction on the server.
This is possible in pouchdb and i am able to achieve that.
But i am wondering how can i achieve the same at server side, in java using lightcouch.
Or is there any Java client-API available that provides this kind of functionality. ??
To find all documents whose _ids match a certain prefix, you only need to do:
/_all_docs?startkey="foo"&endkey="foo\uffff"
(For the prefix "foo".)
I wrote up a bit about why this works here.
LightCouch aims at providing a simple API
for communicating with CouchDB databases.
What you need is a CouchDB view server-side which you can request with LightCouch.