Clojure RethinkDB subscribe to a changefeed

Question

I am using the Clojure driver for RethinkDB. I want to get change feeds from a query. Here is what I have so far :

(defn change-feed [conn]
  (loop [changes (future
                   (-> (r/db "mydb")
                       (r/table "mytable")
                       r/changes
                       (r/run conn)))]
    (println "date : " ((comp :name :newval) first @changes)) ;;prints nil
    (recur (rest changes))))

It blocks in my REPL when called (which is normal). I then add data using the RethinkDB interface. It prints nil and I get the following error :

IllegalArgumentException Don't know how to create ISeq from: clojure.core$future_call$reify__6736  clojure.lang.RT.seqFrom (RT.java:528)

What am I doing wrong ? I would like to be able to :

take items from this future
know also how many items I can take at once (if several are waiting)

Note : I plan to use manifold to manipulate the result in the end, so any solution using it is completely fine.

Daniel Compton · Accepted Answer · 2015-09-07T02:10:45.990

5

I don't think you need the future block there, the Cursor returned by the clj-rethinkdb library will block until it's ready.

You could also use a doseq instead of a loop which might be more natural.

I'm a maintainer of clj-rethinkdb, and we've got changes coming down the pipe to present a core.async interface and a new Cursor abstraction. If you want to use it early, checkout https://github.com/apa512/clj-rethinkdb/pull/55

edited Sep 07 '15 at 02:10

answered Sep 03 '15 at 22:11

Daniel Compton

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Thank you, I'll have a look at that. Also thanks for making this. Note, I would have been happy with a core.async interface as well. – nha Sep 04 '15 at 08:03
No how do you test in the REPL if the cursor blocks ? – nha Sep 04 '15 at 09:57
You could open up a second REPL? – Daniel Compton Sep 05 '15 at 23:38
I suppose I could... Waiting eagerly for you PR to be merged :) PS: in your answer, you mean "should *not* need" right ? – nha Sep 06 '15 at 10:15

Clojure RethinkDB subscribe to a changefeed

1 Answers1