如何使用Hibernate有选择地更新Spring bean的属性？

Question

Given a domain object like:

class MyPojo
  get/setA
  get/setB
  get/setC

If I use MyPojo as the modelAttribute for a form, that has something like:

 <form:form modelAttribute="myPojo" action="nextPage" method="POST">
    <form:input path="a"/>
    <form:input path="b"/>
 </form> 

And I have a Controller method like:

@RequestMapping(value = {"/nextPage"}, method = RequestMethod.POST)
public String theNextPageMethod(@ModelAttribute("myPojo") MyPojo myPojoObj) {
         //call to a service/dao impl are omitted for brevity
         //but the dao impl does:
        sessionFactory.getCurrentSession().saveOrUpdate(myPojoObj);
}

Spring/Hibernate updates myPojoObj with the form input values for properties "a" and "b" but in my case, it's also setting the value of property "c" to null.

Is this the expected behavior? If so, what is the best practice to preserve any value assigned to property "c"? Is there an annotation or some other way to only update the properties "a" and "b"?

CLARIFICATION: Ideally, I'm looking for something to allow for updating "a" and "b" on one page and "b" and "c" on another and keep all the other properties static for each particular request.

Answer 1

Try Dynamic-Update Attribute it should solve your problem.

@DynamicUpdate

Now only changed columns will be update. See also example http://www.mkyong.com/hibernate/hibernate-dynamic-update-attribute-example/

Answer 2

Where do you want to store the entity's state? Session, view or db?

Add

@SessionAttributes({"myPojo"})

To your controller

Or use a hidden input field in your view with c's value

Or annotate a controller method with @ModelAttribute and return the entity from the db each request

You can also create a new, smaller POJO just for the form(s) and use Dozer to copy values to/from your real entity, and use dynamic update.