Grails - Saving current object replace all previous object's values with null or 0

Question

Below is code which save user object and print the list of users in the console.

index.gsp

<g:form action="signUp" controller="User">
    E-mail Id :: <g:textField name="emailId" type="text"/><br>
    Mobile Number :: <g:textField name="mobileNumber" type="text" /> <br>
    <g:submitButton name="Sign up"/>
</g:form>

User.groovy

class User {
    private String emailId;
    private int mobileNumber;
}

UserController.groovy

class UserController {

    def signUp() {

        def user = new User(params);
        user.save();

        List<User> userList = User.list();

        print "Size of list::"+userList.size();
        for(User user1 : userList){
            print "User Id::"+user1.id; 
            print "Email id::"+user1.emailId;
            print "Mobile Number::"+user1.mobileNumber;
        }
    }
}

For now I haven't added any service layer. Below are my inputs and respective outputs.

Input-1

Email - id : test@test.com 
Mobile number : 1234

Output-1 :

....Size of list::1
User Id::1
Email id::test@test.com
Mobile Number::1234

Which is perfect, now I am inserting one more user.

Input-2

Email - id : sample@sample.com 
Mobile number : 5678

Output-2

Size of list::2
User Id::1
Email id::null
Mobile Number::0
User Id::2
Email id::sample@sample.com
Mobile Number::5678

It will replace all previous record with either null or 0(if int).

Answer 1

you shall never define the domain properties as private fields!