BREAKING CHANGE: remove support for callbacks in pre middleware

docs/migrating_to_9.md

@@ -185,12 +185,14 @@ const { promiseOrCallback } = require('mongoose');
 promiseOrCallback; // undefined in Mongoose 9
 ```
 
-## In `isAsync` middleware `next()` errors take priority over `done()` errors
+## `isAsync` middleware no longer supported
 
-Due to Mongoose middleware now relying on promises and async/await, `next()` errors take priority over `done()` errors.
-If you use `isAsync` middleware, any errors in `next()` will be thrown first, and `done()` errors will only be thrown if there are no `next()` errors.
+Mongoose 9 no longer supports `isAsync` middleware. Middleware functions that use the legacy signature with both `next` and `done` callbacks (i.e., `function(next, done)`) are not supported. We recommend middleware now use promises or async/await.
+
+If you have code that uses `isAsync` middleware, you must refactor it to use async functions or return a promise instead.
 
 ```javascript
+// ❌ Not supported in Mongoose 9
 const schema = new Schema({});
 
 schema.pre('save', true, function(next, done) {
@@ -214,8 +216,16 @@ schema.pre('save', true, function(next, done) {
     25);
 });
 
-// In Mongoose 8, with the above middleware, `save()` would error with 'first done() error'
-// In Mongoose 9, with the above middleware, `save()` will error with 'second next() error'
+// ✅ Supported in Mongoose 9: use async functions or return a promise
+schema.pre('save', async function() {
+  execed.first = true;
+  await new Promise(resolve => setTimeout(resolve, 5));
+});
+
+schema.pre('save', async function() {
+  execed.second = true;
+  await new Promise(resolve => setTimeout(resolve, 25));
+});
 ```
 
 ## Removed `skipOriginalStackTraces` option

lib/helpers/timestamps/setupTimestamps.js

@@ -42,15 +42,13 @@ module.exports = function setupTimestamps(schema, timestamps) {
 
   schema.add(schemaAdditions);
 
-  schema.pre('save', function timestampsPreSave(next) {
+  schema.pre('save', function timestampsPreSave() {
     const timestampOption = get(this, '$__.saveOptions.timestamps');
     if (timestampOption === false) {
-      return next();
+      return;
     }
 
     setDocumentTimestamps(this, timestampOption, currentTime, createdAt, updatedAt);
-
-    next();
   });
 
   schema.methods.initializeTimestamps = function() {
@@ -88,7 +86,7 @@ module.exports = function setupTimestamps(schema, timestamps) {
   schema.pre('updateOne', opts, _setTimestampsOnUpdate);
   schema.pre('updateMany', opts, _setTimestampsOnUpdate);
 
-  function _setTimestampsOnUpdate(next) {
+  function _setTimestampsOnUpdate() {
     const now = currentTime != null ?
       currentTime() :
       this.model.base.now();
@@ -105,6 +103,5 @@ module.exports = function setupTimestamps(schema, timestamps) {
       replaceOps.has(this.op)
     );
     applyTimestampsToChildren(now, this.getUpdate(), this.model.schema);
-    next();
   }
 };

lib/model.js

@@ -2914,7 +2914,6 @@ Model.insertMany = async function insertMany(arr, options) {
     await this._middleware.execPost('insertMany', this, [arr], { error });
   }
 
-
   options = options || {};
   const ThisModel = this;
   const limit = options.limit || 1000;

lib/plugins/validateBeforeSave.js

@@ -6,7 +6,7 @@
 
 module.exports = function validateBeforeSave(schema) {
   const unshift = true;
-  schema.pre('save', false, async function validateBeforeSave(_next, options) {
+  schema.pre('save', false, async function validateBeforeSave(options) {
     // Nested docs have their own presave
     if (this.$isSubdocument) {
       return;

package.json

@@ -20,7 +20,7 @@
   "type": "commonjs",
   "license": "MIT",
   "dependencies": {
-    "kareem": "git+https://github.com/mongoosejs/kareem.git#vkarpov15/v3",
+    "kareem": "git+https://github.com/mongoosejs/kareem.git#vkarpov15/remove-isasync",
     "mongodb": "~6.18.0",
     "mpath": "0.9.0",
     "mquery": "5.0.0",

test/aggregate.test.js

@@ -886,9 +886,9 @@ describe('aggregate: ', function() {
         const s = new Schema({ name: String });
 
         let called = 0;
-        s.pre('aggregate', function(next) {
+        s.pre('aggregate', function() {
           ++called;
-          next();
+          return Promise.resolve();
         });
 
         const M = db.model('Test', s);
@@ -902,9 +902,9 @@ describe('aggregate: ', function() {
       it('setting option in pre (gh-7606)', async function() {
         const s = new Schema({ name: String });
 
-        s.pre('aggregate', function(next) {
+        s.pre('aggregate', function() {
           this.options.collation = { locale: 'en_US', strength: 1 };
-          next();
+          return Promise.resolve();
         });
 
         const M = db.model('Test', s);
@@ -920,9 +920,9 @@ describe('aggregate: ', function() {
       it('adding to pipeline in pre (gh-8017)', async function() {
         const s = new Schema({ name: String });
 
-        s.pre('aggregate', function(next) {
+        s.pre('aggregate', function() {
           this.append({ $limit: 1 });
-          next();
+          return Promise.resolve();
         });
 
         const M = db.model('Test', s);
@@ -980,8 +980,8 @@ describe('aggregate: ', function() {
         const s = new Schema({ name: String });
 
         const calledWith = [];
-        s.pre('aggregate', function(next) {
-          next(new Error('woops'));
+        s.pre('aggregate', function() {
+          return Promise.reject(new Error('woops'));
         });
         s.post('aggregate', function(error, res, next) {
           calledWith.push(error);
@@ -1003,9 +1003,9 @@ describe('aggregate: ', function() {
 
         let calledPre = 0;
         let calledPost = 0;
-        s.pre('aggregate', function(next) {
+        s.pre('aggregate', function() {
           ++calledPre;
-          next();
+          return Promise.resolve();
         });
         s.post('aggregate', function(res, next) {
           ++calledPost;
@@ -1030,9 +1030,9 @@ describe('aggregate: ', function() {
 
         let calledPre = 0;
         const calledPost = [];
-        s.pre('aggregate', function(next) {
+        s.pre('aggregate', function() {
           ++calledPre;
-          next();
+          return Promise.resolve();
         });
         s.post('aggregate', function(res, next) {
           calledPost.push(res);
@@ -1295,11 +1295,10 @@ describe('aggregate: ', function() {
   it('cursor() errors out if schema pre aggregate hook throws an error (gh-15279)', async function() {
     const schema = new Schema({ name: String });
 
-    schema.pre('aggregate', function(next) {
+    schema.pre('aggregate', function() {
       if (!this.options.allowed) {
         throw new Error('Unauthorized aggregate operation: only allowed operations are permitted');
       }
-      next();
     });
 
     const Test = db.model('Test', schema);

test/docs/discriminators.test.js

@@ -164,17 +164,15 @@ describe('discriminator docs', function() {
 
     const eventSchema = new mongoose.Schema({ time: Date }, options);
     let eventSchemaCalls = 0;
-    eventSchema.pre('validate', function(next) {
+    eventSchema.pre('validate', function() {
       ++eventSchemaCalls;
-      next();
     });
     const Event = mongoose.model('GenericEvent', eventSchema);
 
     const clickedLinkSchema = new mongoose.Schema({ url: String }, options);
     let clickedSchemaCalls = 0;
-    clickedLinkSchema.pre('validate', function(next) {
+    clickedLinkSchema.pre('validate', function() {
       ++clickedSchemaCalls;
-      next();
     });
     const ClickedLinkEvent = Event.discriminator('ClickedLinkEvent',
       clickedLinkSchema);

test/document.modified.test.js

@@ -323,9 +323,8 @@ describe('document modified', function() {
       });
 
       let preCalls = 0;
-      childSchema.pre('save', function(next) {
+      childSchema.pre('save', function() {
         ++preCalls;
-        next();
       });
 
       let postCalls = 0;