flow like the river

BACK_BACK/node_modules/mongoose/lib/cast/objectid.js

@@ -0,0 +1,29 @@
+'use strict';
+
+const isBsonType = require('../helpers/isBsonType');
+const ObjectId = require('../types/objectid');
+
+module.exports = function castObjectId(value) {
+  if (value == null) {
+    return value;
+  }
+
+  if (isBsonType(value, 'ObjectId')) {
+    return value;
+  }
+
+  if (value._id) {
+    if (isBsonType(value._id, 'ObjectId')) {
+      return value._id;
+    }
+    if (value._id.toString instanceof Function) {
+      return new ObjectId(value._id.toString());
+    }
+  }
+
+  if (value.toString instanceof Function) {
+    return new ObjectId(value.toString());
+  }
+
+  return new ObjectId(value);
+};