strange Mongoose behaviour - document will not save into DB

There were a few problems. Firstly you have a for loop that is firing of async removes, but these were likely not completing before your first callback was called. Better to use Async.each instead.

Also there seems to be some function naming collision happening. So for a complete example of this see the following:

var mongoose = require('mongoose'),    Async = require('async'),    Schema = mongoose.Schema;mongoose.connect('mongodb://localhost/test');var planSchema = new Schema({  title: String,  body: String});var Plan = mongoose.model('Plan',planSchema);Async.series([  function(call1) {    Plan.find(function(err,docs) {      if (err)        throw err;      if ( docs.length > 0 ) {        Async.each( docs, function(d, call2) {          Plan.remove(d, function(err) {            if (err)              throw err;            console.log( "deleting: " + d );            call2();          });        });      }    });    call1();  },  function(call3) {    var planArray = [      { title: 'Plan A', body: 'Plan A' },      { title: 'Plan B', body: 'Plan B' }    ];    var arrayLength = planArray.length;    for ( var i = 0; i < arrayLength; i++ ) {      var p = new Plan(planArray[i]);      p.save(function(err,saved) {        if (err)          throw err;        console.log( "saving: " + saved );      });    }    call3();  }]);

My guess is the latter--a misunderstanding of async flow. Your callback on the first function is invoked before you finish finding and removing documents. So while you're still finding and removing them, you are already adding some more in the second function--but these will be found and removed by the first.

You need to call the first callback only after deleting all documents. Try putting an async.each within your Plan.find callback:

Async.series([    function(callback){        // delete all records        Plan.find(function(err, docs){            Async.each(                docs, // your array                function removeDoc(d, cb) { // iterator function                    Plan.remove(d, function (err) {                        if (err) console.log("error removing records " + err);                        return cb();                    });                },                 callback // executed after the iterator is done            );    },    ...

Incidentally, I believe Plan.remove({}, function(err){...}) deletes all documents--no need to iterate over each document unless of course you're doing something else.

Second function starts execution after you call callback(), i. e. before find and remove calls. You have to wait until find and remove are done and the call callback().Have a look at queue method from async: https://github.com/caolan/async#queue