fix compatibility issue

src/types/cuid.ts

@@ -16,20 +16,20 @@ class SchemaTypeCUID extends SchemaType<string> {
    */
   cast(value?: string): string {
     if (value == null && this.options.required) {
-      return nanoid();
+      return 'cuid' + nanoid();
     }
 
     return value;
   }
 
   /**
-   * Validates data. A valid CUID must be 21 in length.
+   * Validates data. A valid CUID must be started with `c` and 25 in length.
    *
    * @param {*} value
    * @return {String|Error}
    */
   validate(value?: string): string {
-    if (value && (value.length !== 21)) {
+    if (value && (value[0] !== 'c' || value.length !== 25)) {
       throw new ValidationError(`\`${value}\` is not a valid CUID`);
     }
 

test/scripts/model.ts

@@ -214,7 +214,7 @@ describe('Model', () => {
   }).then(data => User.removeById(data._id)));
 
   it('save() - sync problem', () => {
-    const id = nanoid();
+    const id = 'cuid' + nanoid();
 
     return Promise.all([
       User.save({_id: id, age: 1}),

test/scripts/types/cuid.ts

@@ -18,7 +18,7 @@ describe('SchemaTypeCUID', () => {
   });
 
   it('validate()', () => {
-    const id = nanoid();
+    const id = 'cuid' + nanoid();
     type.validate(id).should.eql(id);
 
     (() => type.validate('foo')).should.to.throw(ValidationError, '`foo` is not a valid CUID');