Problems With Sequelize Promises And Normal Node.js Callbacks

I'm using Sequelize in an application that uses normal node.js style callbacks in most of its code. Sequelize uses promises though, so a lot of code ends up looking something like

Solution 1:

Since sequelize uses Bluebird promises, you should be able to do this:

model.find({where: {...}).nodeify(callback);

Solution 2:

It seems that there are a few different solutions to this.

First, to clarify the problem I was having with a more detailed example. Here you can see that the .catch handler gets invoked when the error is thrown in the callback, which isn't what I wanted:

callback = (err, res) ->
    console.log "Called with err: #{err} res: #{res}"
    throw new Error()

models.User.find({where: {...}}).then (user) ->
    callback(null, user)
.catch (err) ->
    callback(err)

Here's the output, where you can see the callback getting invoked twice:

Called with err: null res: [object SequelizeInstance:User]
Called with err: Error res: undefined
Unhandled rejection Error
  at callback (./scripts/nodeify_test.coffee:5:15)
  at [object Object].<anonymous> (./scripts/nodeify_test.coffee:10:5)
  at [object Object].tryCatcher (./node_modules/sequelize/node_modules/bluebird/js/main/util.js:24:31)
  at Promise._settlePromiseFromHandler (./node_modules/sequelize/node_modules/bluebird/js/main/promise.js:454:31)
  at Promise._settlePromiseAt (./node_modules/sequelize/node_modules/bluebird/js/main/promise.js:530:18)
  at Promise._settlePromises (./node_modules/sequelize/node_modules/bluebird/js/main/promise.js:646:14)
  at Async._drainQueue (./node_modules/sequelize/node_modules/bluebird/js/main/async.js:177:16)
  at Async._drainQueues (./node_modules/sequelize/node_modules/bluebird/js/main/async.js:187:10)
  at Async.drainQueues (./node_modules/sequelize/node_modules/bluebird/js/main/async.js:15:14)
  at process._tickCallback (node.js:419:13)

Changing the order of .then .catch

Bergi pointed to When is .then(success, fail) considered an antipattern for promises? which gives the example of calling .catch before .then, and I confirmed that solves the problem:

callback = (err, res) ->
    console.log "Called with err: #{err} res: #{res}"
    throw new Error()

models.User.find({where: {...}}).catch (err) ->
    callback(err)
.then (user) ->
    callback(null, user)

Here's the output:

Called with err: null res: [object SequelizeInstance:User]
Unhandled rejection Error
  at callback (./scripts/nodeify_test.coffee:5:15)
  at [object Object].<anonymous> (./scripts/nodeify_test.coffee:10:5)
  at [object Object].tryCatcher (./node_modules/sequelize/node_modules/bluebird/js/main/util.js:24:31)
  at Promise._settlePromiseFromHandler (./node_modules/sequelize/node_modules/bluebird/js/main/promise.js:454:31)
  at Promise._settlePromiseAt (./node_modules/sequelize/node_modules/bluebird/js/main/promise.js:530:18)
  at Promise._settlePromises (./node_modules/sequelize/node_modules/bluebird/js/main/promise.js:646:14)
  at Async._drainQueue (./node_modules/sequelize/node_modules/bluebird/js/main/async.js:177:16)
  at Async._drainQueues (./node_modules/sequelize/node_modules/bluebird/js/main/async.js:187:10)
  at Async.drainQueues (./node_modules/sequelize/node_modules/bluebird/js/main/async.js:15:14)
  at process._tickCallback (node.js:419:13)

Using .nodeify

cassjj also pointed to nodeify, which effectively turns the promises into normal node code:

callback = (err, res) ->
    console.log "Called with err: #{err} res: #{res}"
    throw new Error()

models.User.find({where: {...}}).nodeify callback

Here the output matches the .catch .then example:

Called with err: null res: [object SequelizeInstance:User]

./node_modules/sequelize/node_modules/bluebird/js/main/async.js:43
        fn = function () { throw arg; };
                                 ^
Error
  at [object Object].callback (./scripts/nodeify_test.coffee:5:15)
  at [object Object].tryCatcher (./node_modules/sequelize/node_modules/bluebird/js/main/util.js:24:31)
  at Promise.successAdapter [as _fulfillmentHandler0] (./node_modules/sequelize/node_modules/bluebird/js/main/nodeify.js:22:30)
  at Promise._settlePromiseAt (./node_modules/sequelize/node_modules/bluebird/js/main/promise.js:528:21)
  at Promise._settlePromises (./node_modules/sequelize/node_modules/bluebird/js/main/promise.js:646:14)
  at Async._drainQueue (./node_modules/sequelize/node_modules/bluebird/js/main/async.js:177:16)
  at Async._drainQueues (./node_modules/sequelize/node_modules/bluebird/js/main/async.js:187:10)
  at Async.drainQueues (./node_modules/sequelize/node_modules/bluebird/js/main/async.js:15:14)
  at process._tickCallback (node.js:419:13)

I also confirmed that I see the same result even if I add a catch handler:

 models.User.find({where: {...}}).nodeify callback
.catch (err) ->
    callback.call({}, err)

I'm going to go with .nodeify.