Question

I have an entity with several fields, but on one view i want to only edit one of the fields. for example… I have a user entity, user has, id, name, address, username, pwd, and so on. on one of the views i want to be able to change the pwd(and only the pwd). so the view only knows of the id and sends the pwd. I want to update my entity without loading the rest of the fields(there are many many more) and changing the one pwd field and then saving them ALL back to the database. has anyone tried this. or know where i can look. all help is greatly appreciated.

Thx in advance.

PS
i should have given more detail. im using hibernate, roo is creating my entities. I agree that each view should have its own entity, problem is, im only building controllers, everything was done before. we were finders from the service layer, but we wanted to use some other finders, they seemed to not be accessible through the service layer, the decision was made to blow away the service layer and just interact with the entities directly (through the finders), the UserService.update(user) is no longer an option. i have recently found a User.persist() and a User.merge(), does the merge update all the fields on the object or only the ones that are not null, or if i want one to now be null how would it know the difference?

Answer 1

Which technologies except Spring are you using?

First of all have separate DTOs for every view, stripped only to what’s needed. One DTO for id+password, another for address data, etc. Remember that DTOs can inherit from each other, so you can avoid duplication. And never pass business/ORM entities directly to view. It is too risky, leaks in some frameworks might allow users to modify fields which you haven’t intended.

After the DTO comes back from the view (most web frameworks work like this) simply load the whole entity and fill only the fields that are present in the DTO.

But it seems like it’s the persistence that is troubling you. Assuming you are using Hibernate, you can take advantage of dynamic-update setting:

dynamic-update (optional – defaults to false): specifies that UPDATE SQL should be generated at runtime and can contain only those columns whose values have changed.

In this case you are still loading the whole entity into memory, but Hibernate will generate as small UPDATE as possible, including only modified (dirty) fields.

Another approach is to have separate entities for each use-case/view. So you’ll have an entity with only id and password, entity with only address data, etc. All of them are mapped to the same table, but to different subset of columns. This easily becomes a mess and should be treated as a last resort.