Validating a domain object for persistence - validation

Question

In the system I'm currently working on, I'm following SRP (I think!) by separating the validation of domain business rules vs persistence constraints. Let's employ the overused customer example. Say a customer must have a valid zip code, street address and name to satisfy the system's business rules. Let's further say that the customer's selected user name must be unique across all customers, which I define as a persistence constraint. Please consider the following "not ready for production" pseudo code:
public interface IPersistenceValidator<T>
{
bool IsValidForPersistence(T domainObj, IList<ValidationError> validationErrors);
}
public interface IValidatable
{
bool IsValid(IList<ValidationError> validationErrors);
}
public class Customer : IValidatable
{
public bool IsValid(IList<ValidationError> validationErrors)
{
//check for business rule compliance
}
}
public class CustomerDao : IPersistenceValidator<Customer>
{
public bool IsValidForPersistence(Customer domainObj, IList<ValidationError> validationErrors)
{
//check for persistence constraint compliance (user name is unique)
}
public bool SaveCustomer(Customer customer)
{
//save customer
}
}
The classes defined above might get wired up into a service class as follows:
public class SaveCustomerService
{
private CustomerDao _customerDao;
public SaveCustomerService(CustomerDao customerDao)
{
_customerDao = customerDao;
}
public bool SaveCustomer(Customer customer)
{
IList<ValidationError> validationErrors = new List<ValidationError>();
if (customer.IsValid(validationErrors))
{
if (_customerDao.IsValidForPersistence(customer, validationErrors))
{
return _customerDao.SaveCustomer(customer);
}
else
{
return false;
}
}
else
{
return false;
}
}
}
My primary concern with this approach is that future consumers of CustomerDao must know to call IsValidForPersistence() before SaveCustomer(), otherwise invalid data gets persisted. I could create DB constraints to guard against this at the SQL levels, but that feels like a kludge.
It seems like IsValidForPersistence() should be moved into CustomerDao.SaveCustomer() but then I have to refactor the signature of SaveCustomer() to include references to the ValidationErrors class. Before I dive into that big of a refactoring, I wanted to get some feedback from others on common/preffered patterns for dealing with these issues.
Thanks

Answer 1

first check HERE if you want to solve your validation problem like;
public class Address {
#NotNull private String line1;
private String line2;
private String zip;
private String state;
#Length(max = 20)
#NotNull
private String country;
#Range(min = -2, max = 50, message = "Floor out of range")
public int floor;
...
}
anyway you must check username in database. You can customize your validation (like go and check DB for that is unique). Look at another links to detail.
Check hibernate validator
Check Using the Validator framework from jboss
You can read Validation In The Domain Layer partI, partII, this is not java but logic is important.