how should I process a set of async commands driven by a loop?

Question

Say I want to insert a group of Store records into the database and call a callback when they are all complete:

insertStores = (db, stores, callback) ->
  sql = ""
  processed = 0
  for store in stores
    do (store) ->
      # build sql
      sql = "some built sql goes here" 

      processQuery(db, sql, ->
        ++processed
        if processed >= stores.length
          callback?()
      )

I'm wondering if there's a more readable way to do this that will get rid of the processed variable. It's important that all inserts get processed before the callback is fired. I don't want to bring in any async to sync libraries. This is for a script, not an application.

Is there a better way to do this in coffeescript? I'm wondering if there's an elegant coffee-ish solution that I'm not aware of.

I understand that you want to find a simple coffee-ish way. I'm afraid there is no way (yet), maybe some day with generators of ES6. But BTW isn't it possible to concat the SQL an do a bulk insert? Is this MySQL? And I wouldn't bother using async or Seq when doing server-side programming. It's more readable to other node.js programmers than detecting what you want to achieve with constructs like if i == stores.length - 1. — hgoebl
– hgoebl, Commented Feb 24, 2014 at 21:43
"But BTW isn't it possible to concat the SQL an do a bulk insert?" yes, but I can just as easily ask this question for other async operations that don't concatenate well. — jcollum
– jcollum, Commented Feb 24, 2014 at 21:47

Brian Ensink · Accepted Answer · 2014-02-24 22:14:50Z

1

Do you specifically need a CoffeeScript way of doing this? I think the Async package would be a good thing to use. It has a number of functions to let you run asynchronous tasks in series or parallel and get a single callback when everything is finished.

answered Feb 24, 2014 at 22:14

Brian Ensink

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1 Comment

jcollum Over a year ago

Well, yeah, that is what I asked for. I'm looking for a native solution. I want to know if there is a better way to do this without bringing in a library.

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