DAO reusability

Question

Hello,
I have a question regarding DAO�s.
DAO�s help solve the problem of switching you data access layer, that I know. I wonder however how reusable they are. An example:
UserProfileDAO declares the method findUserProfile(int userId) and returns a UserProfile instance.
In the next project I need the user profile to contain more properties e.g. the date of his last visit. The UserProfile class would be extended by the SpecificUserProfile class to hold these new properties.
However when I�m using the UserProfileDAO in my new project I�ll need to cast from UserProfile to SpecificUserProfile all the time when calling findUserProfileById(..).
A solution would be to define the SpecificUserProfileDAO and declare another find method that has the correct return type: SpecificUserProfile. This solves my cast problem but leaves me with 2 find by id methods in my SpecificUserProfileDAO interface that do the exact same thing. The only difference is the return type.
Can anyone tell me how this could be done in a cleaner way?
If I�m being to picky just tell me ;-)
Regards,
Wim

Answer 1

However when I�m using the UserProfileDAO in my new
project I�ll need to cast from UserProfile to
SpecificUserProfile all the time when calling
findUserProfileById(..).Not a real big problem.
A solution would be to define the
SpecificUserProfileDAO and declare another find
method that has the correct return type:
SpecificUserProfile. This solves my cast problem but
leaves me with 2 find by id methods in my
SpecificUserProfileDAO interface that do the exact
same thing. The only difference is the return type.Does this work for you?public SpecificUserProfile findSpecificUserById(int) {...}
public UserProfile findUserById(int) {
   return new UserProfile(findSpecificUserById(int))
};