fix: correctly apply schema-level discriminators when compiling model…

… re: #7971

lib/helpers/model/discriminator.js

@@ -108,7 +108,7 @@ module.exports = function discriminator(model, name, schema, tiedValue, applyPlu
 
     utils.merge(schema, baseSchema, {
       isDiscriminatorSchemaMerge: true,
-      omit: { discriminators: true, base: true },
+      omit: { discriminators: true, base: true, _applyDiscriminators: true },
       omitNested: conflictingPaths.reduce((cur, path) => {
         cur['tree.' + path] = true;
         return cur;
@@ -140,7 +140,6 @@ module.exports = function discriminator(model, name, schema, tiedValue, applyPlu
     obj[key][schema.options.typeKey] = existingPath ? existingPath.options[schema.options.typeKey] : String;
     schema.add(obj);
 
-
     schema.discriminatorMapping = { key: key, value: value, isRoot: false };
 
     if (baseSchema.options.collection) {

lib/index.js

@@ -522,9 +522,6 @@ Mongoose.prototype.model = function(name, schema, collection, options) {
   }
 
   const model = _mongoose._model(name, schema, collection, options);
-  for (const disc in schema._applyDiscriminators) {
-    model.discriminator(disc, schema._applyDiscriminators[disc]);
-  }
   _mongoose.connection.models[name] = model;
   _mongoose.models[name] = model;
 
@@ -536,7 +533,6 @@ Mongoose.prototype.model = function(name, schema, collection, options) {
  */
 
 Mongoose.prototype._model = function(name, schema, collection, options) {
-
   const _mongoose = this instanceof Mongoose ? this : mongoose;
 
   let model;
@@ -572,6 +568,12 @@ Mongoose.prototype._model = function(name, schema, collection, options) {
 
   connection.emit('model', model);
 
+  if (schema._applyDiscriminators != null) {
+    for (const disc of Object.keys(schema._applyDiscriminators)) {
+      model.discriminator(disc, schema._applyDiscriminators[disc]);
+    }
+  }
+
   return model;
 };
 

lib/schema.js

@@ -371,6 +371,9 @@ Schema.prototype._clone = function _clone(Constructor) {
   if (this.discriminators != null) {
     s.discriminators = Object.assign({}, this.discriminators);
   }
+  if (this._applyDiscriminators != null) {
+    s._applyDiscriminators = Object.assign({}, this._applyDiscriminators);
+  }
 
   s.aliases = Object.assign({}, this.aliases);
 
@@ -470,9 +473,9 @@ Schema.prototype.defaultOptions = function(options) {
   return options;
 };
 
-Schema.prototype.discriminator = function(name, obj) {
+Schema.prototype.discriminator = function(name, schema) {
   this._applyDiscriminators = {};
-  this._applyDiscriminators[name] = obj;
+  this._applyDiscriminators[name] = schema;
 };
 
 /**

test/schema.test.js

@@ -2732,32 +2732,35 @@ describe('schema', function() {
     const foundUser = await User.findOne({ _id: user._id });
     assert.ok(Array.isArray(foundUser.data));
   });
-  it('sets an _applyDiscriminators property on the schema and add discriminator to appropriate model gh-7971-p2', async() => {
+
+  it('sets an _applyDiscriminators property on the schema and add discriminator to appropriate model (gh-7971)', async() => {
     const eventSchema = new mongoose.Schema({ message: String },
-      { discriminatorKey: 'kind', _id: false });
+      { discriminatorKey: 'kind' });
     const batchSchema = new mongoose.Schema({ name: String }, { discriminatorKey: 'kind' });
     batchSchema.discriminator('event', eventSchema);
     assert(batchSchema._applyDiscriminators);
+    assert.ok(!eventSchema._applyDiscriminators);
+
     const arraySchema = new mongoose.Schema({ array: [batchSchema] });
     const arrayModel = db.model('array', arraySchema);
     const array = await arrayModel.create({
       array: [{ name: 'Array Test', message: 'Please work', kind: 'event' }]
     });
-    console.log(array);
     assert(array.array[0].message);
+
     const parentSchema = new mongoose.Schema({ sub: batchSchema });
     const Parent = db.model('Parent', parentSchema);
     const parent = await Parent.create({
       sub: { name: 'Sub Test', message: 'I hope I worked!', kind: 'event' }
     });
     assert(parent.sub.message);
+
     const Batch = db.model('Batch', batchSchema);
     const batch = await Batch.create({
       name: 'Test Testerson',
       message: 'Hello World!',
       kind: 'event'
     });
-    console.log('batch', batch, batch.message);
     assert(batch.message);
   });
 });