perf(model): skip $toObject() for insertMany with only primitive values

Re: #14719

Author: vkarpov15

lib/document.js

@@ -3811,13 +3811,7 @@ Document.prototype.$__handleReject = function handleReject(err) {
 Document.prototype.$toObject = function(options, json) {
   const defaultOptions = this.$__schema._defaultToObjectOptions(json);
 
-  const hasOnlyPrimitiveValues = !this.$__.populated && !this.$__.wasPopulated && (this._doc == null || Object.values(this._doc).every(v => {
-    return v == null
-      || typeof v !== 'object'
-      || (utils.isNativeObject(v) && !Array.isArray(v))
-      || isBsonType(v, 'ObjectId')
-      || isBsonType(v, 'Decimal128');
-  }));
+  const hasOnlyPrimitiveValues = this.$__hasOnlyPrimitiveValues();
 
   // If options do not exist or is not an object, set it to empty object
   options = utils.isPOJO(options) ? { ...options } : {};
@@ -3867,27 +3861,10 @@ Document.prototype.$toObject = function(options, json) {
   // const originalTransform = options.transform;
 
   let ret;
-  if (hasOnlyPrimitiveValues) {
+  if (hasOnlyPrimitiveValues && !options.flattenObjectIds) {
     // Fast path: if we don't have any nested objects or arrays, we only need a
     // shallow clone.
-    if (this._doc == null) {
-      ret = {};
-    }
-    ret = {};
-    if (this._doc != null) {
-      for (const key of Object.keys(this._doc)) {
-        const value = this._doc[key];
-        if (value instanceof Date) {
-          ret[key] = new Date(value);
-        } else if (value === undefined) {
-          delete ret[key];
-        } else if (options.flattenObjectIds && isBsonType(value, 'ObjectId')) {
-          ret[key] = value.toJSON();
-        } else {
-          ret[key] = value;
-        }
-      }
-    }
+    ret = this.$__toObjectInternal();
   } else {
     ret = clone(this._doc, options) || {};
   }
@@ -3948,6 +3925,26 @@ Document.prototype.$toObject = function(options, json) {
   return ret;
 };
 
+/*!
+ * Internal shallow clone alternative to `$toObject()`: much faster, no options processing
+ */
+
+Document.prototype.$__toObjectInternal = function $__toObjectInternal() {
+  const ret = {};
+  if (this._doc != null) {
+    for (const key of Object.keys(this._doc)) {
+      const value = this._doc[key];
+      if (value instanceof Date) {
+        ret[key] = new Date(value);
+      } else if (value !== undefined) {
+        ret[key] = value;
+      }
+    }
+  }
+
+  return ret;
+};
+
 /**
  * Converts this document into a plain-old JavaScript object ([POJO](https://masteringjs.io/tutorials/fundamentals/pojo)).
  *
@@ -5328,6 +5325,20 @@ Document.prototype.$clearModifiedPaths = function $clearModifiedPaths() {
   return this;
 };
 
+/*!
+ * Check if the given document only has primitive values
+ */
+
+Document.prototype.$__hasOnlyPrimitiveValues = function $__hasOnlyPrimitiveValues() {
+  return !this.$__.populated && !this.$__.wasPopulated && (this._doc == null || Object.values(this._doc).every(v => {
+    return v == null
+      || typeof v !== 'object'
+      || (utils.isNativeObject(v) && !Array.isArray(v))
+      || isBsonType(v, 'ObjectId')
+      || isBsonType(v, 'Decimal128');
+  }));
+};
+
 /*!
  * Module exports.
  */

lib/model.js

@@ -2951,7 +2951,10 @@ Model.$__insertMany = function(arr, options, callback) {
       }
       const shouldSetTimestamps = (!options || options.timestamps !== false) && doc.initializeTimestamps && (!doc.$__ || doc.$__.timestamps !== false);
       if (shouldSetTimestamps) {
-        return doc.initializeTimestamps().toObject(internalToObjectOptions);
+        doc.initializeTimestamps();
+      }
+      if (doc.$__hasOnlyPrimitiveValues()) {
+        return doc.$__toObjectInternal();
       }
       return doc.toObject(internalToObjectOptions);
     });