fix(model): allow calling Model.init() again after calling `dropDat…

…abase()`

Fix #6967

lib/connection.js

@@ -59,6 +59,9 @@ function Connection(base) {
   this._readyState = STATES.disconnected;
   this._closeCalled = false;
   this._hasOpened = false;
+
+  this.$internalEmitter = new EventEmitter();
+  this.$internalEmitter.setMaxListeners(0);
 }
 
 /*!
@@ -327,6 +330,7 @@ Connection.prototype.dropCollection = _wrapConnHelper(function dropCollection(co
  */
 
 Connection.prototype.dropDatabase = _wrapConnHelper(function dropDatabase(cb) {
+  this.$internalEmitter.emit('dropDatabase');
   this.db.dropDatabase(cb);
 });
 

lib/model.js

@@ -982,14 +982,22 @@ for (const i in EventEmitter.prototype) {
 Model.init = function init(callback) {
   this.schema.emit('init', this);
 
-  if (this.$init) {
+  if (this.$init != null) {
     if (callback) {
       this.$init.then(() => callback(), err => callback(err));
       return null;
     }
     return this.$init;
   }
 
+  // If `dropDatabase()` is called, this model's collection will not be
+  // init-ed. It is sufficiently common to call `dropDatabase()` after
+  // `mongoose.connect()` but before creating models that we want to
+  // support this. See gh-6967
+  this.db.$internalEmitter.once('dropDatabase', () => {
+    delete this.$init;
+  });
+
   const Promise = PromiseProvider.get();
   const autoIndex = this.schema.options.autoIndex;
   this.$init = new Promise((resolve, reject) => {

lib/statemachine.js

@@ -84,9 +84,9 @@ StateMachine.prototype._changeState = function _changeState(path, nextState) {
  */
 
 StateMachine.prototype.clear = function clear(state) {
-  let keys = Object.keys(this.states[state]),
-      i = keys.length,
-      path;
+  const keys = Object.keys(this.states[state]);
+  let i = keys.length;
+  let path;
 
   while (i--) {
     path = keys[i];
@@ -122,9 +122,9 @@ StateMachine.prototype.some = function some() {
 
 StateMachine.prototype._iter = function _iter(iterMethod) {
   return function() {
-    let numArgs = arguments.length,
-        states = utils.args(arguments, 0, numArgs - 1),
-        callback = arguments[numArgs - 1];
+    const numArgs = arguments.length;
+    let states = utils.args(arguments, 0, numArgs - 1);
+    const callback = arguments[numArgs - 1];
 
     if (!states.length) states = this.stateNames;
 

test/model.test.js

@@ -5864,6 +5864,8 @@ describe('Model', function() {
   });
 
   it('dropDatabase() after init allows re-init (gh-6967)', function() {
+    const db = mongoose.createConnection(start.uri + '_6967');
+
     const Model = db.model('gh6640', new Schema({
       name: { type: String, index: true }
     }));
@@ -5876,7 +5878,7 @@ describe('Model', function() {
       assert.ok(!Model.$init);
 
       let threw = false;
-      
+
       try {
         yield Model.listIndexes();
       } catch (err) {