Question

I have just one week experience in GAE/Java and trying to port an legacy application(developed using PHP/MySQL) to GAE+JDO. I’m now stuck with a basic issue in creating a relationship between two tables(kinds in GAE).

So here is the case:
We have a Users table which holds the user authentication information. It also has a field user_role which store role_id, which is actually a foreign key of another table user_roles.

From the the Entity-Relationship documentation in GAE, I understand that DataStore doesn’t support foreign-key relationships and designed the Users class by adapting the Employee-ContactInfo example in the docs.

When I executed the application, the user_roles kind is inserted each time I add an entry in Users table. The user_roles kind is supposed to have only three static values. But this is having redundant values as I input more records in Users.

I think that I’m missing something very trivial, but I couldn’t figure it out due to my inexperience to datastore. It would be very nice if someone could guide me to solve this issue.

Here is the code:

@PersistenceCapable(identityType = IdentityType.APPLICATION)
public class Users {

        @PrimaryKey
        @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
        private Key key;

        @Persistent
        private String userName;

        @Persistent
        private String password;

        @Persistent
        private String salt;

        @Persistent
        private Date createdDate;

        @Persistent
        private Key createdBy;

        @Persistent
        private Date lastLogin;

        @Persistent
        private boolean status;

        @Persistent
        private String authKey;

        @Persistent(defaultFetchGroup="true")
        private SecurityRole securityRole;

        @Autowired
        SecurityRepository securityRepository ;

        public SecurityPrincipals(String userName, String password,SecurityRole securityRole,boolean status) {
                this.securityRole = securityRole;
                this.userName = userName;
                this.password = password;
                this.status = status;
        }

   //getters and setters
}

Definition for Roles:

@PersistenceCapable(detachable="true")
public class SecurityRole {

        @PrimaryKey
        @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
        private Key key;

        @Persistent
        private String securityRoleName;

        @Persistent
        private String securityRoleDescription;

        @Persistent
        private String securityRoleStatus;

        @Persistent
        private Date securityRoleCreatedDate;

        public SecurityRole(String securityRoleName, String securityRoleDescription, String securityRoleStatus,String securityBaseType)
        {
                this.securityRoleName = securityRoleName;
                this.securityRoleDescription = securityRoleDescription;
                this.securityRoleStatus = securityRoleStatus;
                this.securityBaseType = securityBaseType;
        }
// getters and setters
}

The relevant code from Controller:

SecurityRole securityRole = securityRepository.getSecurityRole( securityRoleName);
users = new Users(userName,password,status,securityRole);
iUserRepository.save(employeeDetails);

Here is the definition of getSecurityRole:

public SecurityRole getSecurityRole(String securityRoleName)
        {
                      PersistenceManagerFactory pmf = this.jdoTemplate.getPersistenceManagerFactory();
                PersistenceManager pm = pmf.getPersistenceManager();
                try {
                        Query query = pm.newQuery( SecurityRole.class);
                        query.declareImports("import java.lang.String");
                        query.declareParameters("String securityRoleName");
                        query.setFilter("this.securityRoleName == securityRoleName");
                        List<SecurityRole> securityRoles = (List<SecurityRole>)query.execute(new String(securityRoleName));
                        SecurityRole temp = null;
                        for(SecurityRole securityRole: securityRoles)
                        {
                                temp = securityRole;
                        }
            return temp;
                }
                finally {
                        pm.close();
                }
        }

Here is the definition of iUserRepository.save():

public void save(Users user) {
               jdoTemplate.makePersistent(companyDetails);
}

Answer 1

In the Users class, you have the defined the property

@Persistent(defaultFetchGroup="true")
private SecurityRole securityRole;

This statement creates an “owned” relationship in GAE datastore, which means that when you create an object of the Users class, an object of the SecurityRole class will be created as well.

What you need, is an unowned relationship that can be created as follows:

@Persistent(defaultFetchGroup="true")
private Key securityRole;

In this way, a SecurityRole object is not created each time you create an instance of the Users class. For more information about owned and unowned relationships, take a look at http://code.google.com/appengine/docs/java/datastore/jdo/relationships.html

Hope this helps!