David,
This is my "snippet" for consuming a continuous _changes feed using
node. Take a look and and see what you think. We can take it offline to
discuss in detail if you wish.
Best regards
cliff
var
sys = require("sys"),
http = require('http'),
events = require("events"),
host = "10.0.0.10",
port = 5984,
database="test",
changesurl = "http://"+ host +":"+ port.toString() +"/"+database+
"/_changes?feed=continuous&include_docs=true&heartbeat=10000",
infourl = "http://"+ host +":"+port.toString()+"/"+database,
lastsequence=0,
stream = new process.EventEmitter(),
timeout=0;
sys.puts(changesurl);
// set up connection
couchdbconnection = http.createClient(port, host);
// handlers to monitor the actual connection
couchdbconnection.addListener('close', function() {
couchdbconnection.destroy();
return stream.emit('seq', info.update_seq);
});
couchdbconnection.addListener('error',function() {
console.log("couchdbconnection listener ....error");
});
// Send request
sys.puts(infourl);
request = couchdbconnection.request('GET', infourl);
request.end();
// Listen for any responses
request.addListener("response", function(res) {
/* "data" gets triggered on receipt of line end information so no need
to do
any special buffering ...... or at least I dont think so */
res.addListener('data', function(infodata) {
// info comes in as a string
info = JSON.parse(infodata);
});
});
// Wait until the code used to get the last sequence number completes
stream.addListener('seq',function (lastseq) {
// set up connection
couchdbconnection = http.createClient(port, host);
couchdbconnection.setTimeout(timeout);
// handlers to monitor the actual connection
couchdbconnection.addListener('close', function() {
console.log("couchdbconnection Listener .....connection closed");
});
couchdbconnection.addListener('error',function() {
sys.puts("couchdbconnection listener ....error");
});
// Send request
request = couchdbconnection.request('GET',
changesurl+"&since="+lastseq);
request.end();
// Listen for any responses
request.addListener("response", function(res) {
/* "data" gets triggered on receipt of line end information so no need
to do
any special buffering */
res.addListener('data', function(changedata) {
// Couch sends an empty line as the "heartbeat"
if (changedata == "\n") {
console.log("heartbeat");
}
else {
// info comes in as a string so create JSON object to add additional info
changes=JSON.parse(changedata);
changes.database=database;
changedata=JSON.stringify(changes);
console.log("Actual data Changed "+ changedata);
};});});});
On 04/04/11 11:50, David Mitchell wrote:
Hi Cliff,
What you're describing doing using Node.js sounds exactly like what I
want to do - process the uploads transparently in the background,
entirely within the context of my Couchapp.
I've searched around for info on using Node.js and CouchDB like this,
but only found links that describe the technique in very broad detail.
Do you know of any links that describe it in reasonable detail?
I'm an experienced Python/Ruby/C/C#/... coder and an occasional Erlang
coder, but stuff like Node.js is completely new to me - I'm assuming
that if I could see how to do this sort of thing in a fairly concise
example, it'd trigger the "aha" moment in my brain and then I'd be off
and running...
Thanks again
Dave M.
On 4 April 2011 19:34, Cliff Williams <[email protected]
<mailto:[email protected]>> wrote:
David,
I hope you are well.
I think that you have covered your options pretty well.
"- upload the data& save it into a single "uploaded_csv" document in
CouchDB. Within CouchDB, detect the presence of a new "uploaded_csv"
document, extract and process the content using Javascript and
save it into
multiple "data" records, with appropriate indexing, then dispose
of the
"uploaded_csv" document or mark it as "processed". This seems
reasonably
straightforward, but I'm not sure how to detect the presence of a new
"uploaded_csv" document"
This is the approach that I would take.
Couchdb has a quite excellent _changes feed which will notify you
(or can be set up to notify) in real time on any changes made to
specific databases.
I personally would use Node.js to monitor the changes feed and
process your csv files (Javascript and very fast) but you could of
course use anything (erlang python (Ruby's CSV processing
libraries are also quite good)).
best regards
Cliff
On 04/04/11 08:58, David Mitchell wrote:
Hello all,
I'm just about to start on my first (wildly ambitious)
Couchapp. I've had
quite a bit of Erlang experience, but not for the past couple
of years so
I'm a bit rusty. I've had a tiny bit of experience with
CouchDB via various
Python scripts, but that's all been treating CouchDB as a
"black box"
database so I've currently got little knowledge of what it can
do beyond
being a document datastore.
Initially, I'm trying to understand my options for uploading
CSV files,
parsing out the content and storing them in CouchDB (one
CouchDB record per
line of CSV content). While it's reasonably straightforward
to do this if I
was using e.g. Python as a batch load tool, I don't want to go
outside
Javascript for this project if I can avoid it. The CSV files
are anywhere
from 1k-30k records, with 8-10 fields in each that are
straightforward
timestamps and floating point numbers.
For an old-school Web app with distinct database and app
server layers,
there's a straightforward option - upload the data to a file
on the web
server, then process the data out of the file and load it into
your
database. Sure there's variations on this approach such as
saving data as a
database blob, but I'm looking for the best CouchApp-specific
approach if
one exists.
Options I can see:
- upload the data& save it into a single "uploaded_csv"
document in
CouchDB. Within CouchDB, detect the presence of a new
"uploaded_csv"
document, extract and process the content using Javascript and
save it into
multiple "data" records, with appropriate indexing, then
dispose of the
"uploaded_csv" document or mark it as "processed". This seems
reasonably
straightforward, but I'm not sure how to detect the presence
of a new
"uploaded_csv" document (is there a cron equivalent in Couch?)
and I'd have
to track the progress of processing each uploaded CSV file to
detect when
they've been processed into "data" records
- upload the data& save it into a single "uploaded_csv"
document in
CouchDB. Have CouchDB running embedded in an Erlang app, and
use Erlang to
read the "uploaded_csv" data, then send a series of e.g. HTTP
PUTs to load
the data into multiple "data" records in CouchDB. This just
seems ugly to
me, but I'm pretty confident I could get it working pretty easily
- upload the data and process it directly into "data" records
from a web
page served from CouchApp. This seems like it could impact on
scalability
due to having long-running connections between client and
server, but at
least a user would know when their data has been uploaded and
processed
successfully with trivial extra work on my part
- upload the data, convert it to JSON on the client using
clientside
Javascript, then send it as a set of document uploads (i.e.
one document per
CSV record) from the client to the Couch server. This would
let me parse
out any bogus CSV content without sending it to the server,
but I'll have
users running browsers on mobile devices and I'm not sure I
want to put that
processing load onto the client
Are there any "recommended" approaches for this type of task?
I suspect
this question and others I'll ask have probably already been
considered and
dealt with by various experts; if there's a "CouchApp
cookbook" with
recommended solutions for these and other common situations,
I'd appreciate
a pointer to it so I could start to answer my own questions.
Thanks in advance
Dave M.
