How to update a specific fields of class in Fluent NHibernate with out updating the whole object? [duplicate] - nhibernate

Question

This question already has answers here:
NHibernate update on single property updates all properties in sql
(2 answers)
Closed 5 years ago.
I am using Fluent NHibernate to do my NHibernate mappings, but now I have come to a problem that I am not sure how to solve. A simplified version of the problem follows.
I have a user class:
public class User {
public virtual int Id { get; set; }
public virtual string FirstName { get; set; }
public virtual string LastName { get; set; }
}
This is the associated Fluent NHibernate Class Map
public class UserMap : ClassMap<User> {
public UserMap() {
Id(x => x.Id);
Map(x => x.FirstName);
Map(x => x.LastName);
}
}
I have two web forms. One form allows me to change the users first name, and the second form allows me to change the users last name. What I am trying to achieve is a simple SQL statement like this:
For the first form:
UPDATE [users] SET firstname='new first name' WHERE id=1
For the second form:
UPDATE [users] SET lastname='new last name' WHERE id=1
Currently NHibernate performs the following SQL on my database:
UPDATE [users] SET firstname=null, lastname='new last name' WHERE id=1
The problem in the real world application, is that there are too many properties to update on some big objects (as well as access restrictions), and it seems pointless to update the whole object, when all I want / am allowed to do is update a single property.
I am hoping that someone can provide some advice as to how I can realise this, or point me in the right direction to solve this.

Answer 1

Hibernate's doing the right thing, but your problem indicates that your schema needs some normalization.

Answer 2

Ok, that works, Thanks for the help and tips Queen3!
here is how I sovled it:
using (var sf = Repository.CreateSessionFactory()) {
using (var s = sf.OpenSession()) {
using (var t = session.BeginTransaction()) {
var existingUser = s.Get<User>(editedUser.Id);
existingUser.LastName = editedUser.LastName;
s.SaveOrUpdate(existingUser);
t.Commit();
}
}
}
Although this does work, it requires that I retrieve the User from the database first and work within the same session. The good thing is that the sql statement that is generated just updates the dirty LastName field. :-)
I am unable to get it to work with a detached instance of the user, this is similar to how I was doing it before, which resulted in every field of the user being updated.
using (var sf = Repository.CreateSessionFactory()) {
using (var s = sf.OpenSession()) {
using (var t = session.BeginTransaction()) {
s.SaveOrUpdate(editedUser);
t.Commit();
}
}
}