fix: add mongoose.isValidObjectId() function to test whether Mongoo…

…se can cast a value to an objectid

Fix #3823

lib/index.js

@@ -933,6 +933,51 @@ Mongoose.prototype.DocumentProvider = require('./document_provider');
 
 Mongoose.prototype.ObjectId = SchemaTypes.ObjectId;
 
+/**
+ * Returns true if Mongoose can cast the given value to an ObjectId, or
+ * false otherwise.
+ *
+ * ####Example:
+ *
+ *     mongoose.isValidObjectId(new mongoose.Types.ObjectId()); // true
+ *     mongoose.isValidObjectId('0123456789ab'); // true
+ *     mongoose.isValidObjectId(6); // false
+ *
+ * @method isValidObjectId
+ * @api public
+ */
+
+Mongoose.prototype.isValidObjectId = function(v) {
+  if (v == null) {
+    return true;
+  }
+  const base = this || mongoose;
+  const ObjectId = base.driver.get().ObjectId;
+  if (v instanceof ObjectId) {
+    return true;
+  }
+
+  if (v._id != null) {
+    if (v._id instanceof ObjectId) {
+      return true;
+    }
+    if (v._id.toString instanceof Function) {
+      v = v._id.toString();
+      return typeof v === 'string' && (v.length === 12 || v.length === 24);
+    }
+  }
+
+  if (v.toString instanceof Function) {
+    v = v.toString();
+  }
+
+  if (typeof v === 'string' && (v.length === 12 || v.length === 24)) {
+    return true;
+  }
+
+  return false;
+};
+
 /**
  * The Mongoose Decimal128 [SchemaType](/docs/schematypes.html). Used for
  * declaring paths in your schema that should be

test/index.test.js

@@ -712,6 +712,12 @@ describe('mongoose module:', function() {
     });
   });
 
+  it('isValidObjectId (gh-3823)', function() {
+    assert.ok(mongoose.isValidObjectId('0123456789ab'));
+    assert.ok(mongoose.isValidObjectId(new mongoose.Types.ObjectId()));
+    assert.ok(!mongoose.isValidObjectId(6));
+  });
+
   describe('exports', function() {
     function test(mongoose) {
       assert.equal(typeof mongoose.version, 'string');