fix(schema+document): allow disabling _id on subdocuments by default

Re: #11541
Re: #8883

lib/document.js

@@ -136,7 +136,6 @@ function Document(obj, fields, skipId, options) {
   // excluded fields
   if (utils.isPOJO(fields)) {
     exclude = isExclusive(fields);
-
     this.$__.fields = fields;
     this.$__.exclude = exclude;
   }

lib/options/SchemaTypeOptions.js

@@ -130,7 +130,7 @@ Object.defineProperty(SchemaTypeOptions.prototype, 'ref', opts);
  * @instance
  */
 
- Object.defineProperty(SchemaTypeOptions.prototype, 'refPath', opts);
+Object.defineProperty(SchemaTypeOptions.prototype, 'refPath', opts);
 
 /**
  * Whether to include or exclude this path by default when loading documents

lib/schema.js

@@ -1202,6 +1202,7 @@ Schema.prototype.interpretAsType = function(path, obj, options) {
   }
 
   if (type && type.instanceOfSchema) {
+
     return new MongooseTypes.Subdocument(type, path, obj);
   }
 

lib/schema/SubdocumentPath.js

@@ -33,6 +33,13 @@ module.exports = SubdocumentPath;
  */
 
 function SubdocumentPath(schema, path, options) {
+  const schemaTypeIdOption = SubdocumentPath.defaultOptions &&
+    SubdocumentPath.defaultOptions._id;
+  if (schemaTypeIdOption != null) {
+    options = options || {};
+    options._id = schemaTypeIdOption;
+  }
+
   schema = handleIdOption(schema, options);
 
   this.caster = _createConstructor(schema);

test/common.js

@@ -84,6 +84,7 @@ module.exports = function(options) {
 
   const noErrorListener = !!options.noErrorListener;
   delete options.noErrorListener;
+  options.enableUtf8Validation = false;
 
   const conn = mongoose.createConnection(uri, options);
 

test/schema.subdocumentpath.test.js

@@ -181,4 +181,22 @@ describe('SubdocumentPath', function() {
 
     mongoose.Schema.Types.Subdocument.set('required', false);
   });
+
+  it('supports setting _id globally (gh-11541) (gh-8883)', function() {
+    mongoose.deleteModel(/Test/);
+    mongoose.Schema.Types.Subdocument.set('_id', false);
+
+    const Model = mongoose.model('Test', mongoose.Schema({
+      nested: mongoose.Schema({
+        test: String
+      })
+    }));
+
+    const doc = new Model({ nested: {} });
+
+    assert.ok(!doc.nested._id);
+
+    delete mongoose.Schema.Types.Subdocument.defaultOptions._id;
+    mongoose.Schema.Types.Subdocument.set('required', false);
+  });
 });