feat(schematype): merge rather than overwrite default schematype validators

Fix #14070

Author: vkarpov15

lib/schemaType.js

@@ -59,7 +59,19 @@ function SchemaType(path, options, instance) {
   const defaultOptionsKeys = Object.keys(defaultOptions);
 
   for (const option of defaultOptionsKeys) {
-    if (defaultOptions.hasOwnProperty(option) && !Object.prototype.hasOwnProperty.call(options, option)) {
+    if (option === 'validate') {
+      const defaultValidators = Array.isArray(defaultOptions.validate)
+        ? defaultOptions.validate
+        : defaultOptions.validate == null
+          ? []
+          : [defaultOptions.validate];
+      const specifiedValidators = Array.isArray(options.validate)
+        ? options.validate
+        : options.validate == null
+          ? []
+          : [options.validate];
+      options.validate = [...defaultValidators, ...specifiedValidators];
+    } else if (defaultOptions.hasOwnProperty(option) && !Object.prototype.hasOwnProperty.call(options, option)) {
       options[option] = defaultOptions[option];
     }
   }

test/schematype.test.js

@@ -208,6 +208,25 @@ describe('schematype', function() {
     });
   });
 
+  it('merges default validators (gh-14070)', function() {
+    class TestSchemaType extends mongoose.SchemaType {}
+    TestSchemaType.set('validate', v => typeof v === 'string');
+
+    const schemaType = new TestSchemaType();
+    schemaType.validate(v => v.length === 2);
+
+    let err = schemaType.doValidateSync([1, 2]);
+    assert.ok(err);
+    assert.equal(err.name, 'ValidatorError');
+
+    err = schemaType.doValidateSync('foo');
+    assert.ok(err);
+    assert.equal(err.name, 'ValidatorError');
+
+    err = schemaType.doValidateSync('ab');
+    assert.ifError(err);
+  });
+
   describe('set()', function() {
     describe('SchemaType.set()', function() {
       it('SchemaType.set, is a function', () => {