orm - NHibernate SaveOrUpdate without primary key -

the situation

i've got database table mapped via nhibernate (3.3.3-sp1). application running on .net4.0 , mapping done via fluentnhibernate (1.4.0).

create table movies (id int primary key,  yearpublished datetime not null,  name nvarchar(500) not null,  description ntext not null) 

the data this:

 id | yearpublished | name                   | description ---+---------------+------------------------+-------------------------------------------- 1  | 1968          | 2001: space oddyssey | epic drama of adventure , exploration   

the problem

i'm creating new entities of table , want avoid adding more 1 entity same real world thing. know there session.saveorupdate , there way make work composite , natural ids that's not want since entities have primary key , need composite key making sure no duplicates in db.

var movie = new movies {     yearpublished = 1968,     name = "2001: space oddyssey",     description = "an awesome journey jupiter" };  // behavior right now:  // adds new movie besides fact // movie in database // has 2 entries session.saveorupdate(movie);  assert.istrue(movie.id == 2 && movie.description == "an awesome journey jupiter");  // want able define // makes object unique other primary key; // in scenario should combination // of "yearpublished" , "name" session.myawesomesaveorupdate(movie);  assert.istrue(movie.id == 1 && movie.description == "an epic drama of adventure , exploration"); 

is functionality in place in nhibernate (e.g. through custom mapping) or have fetch candidates db , hand?

thanks!

i solve adding unique constraint on natural key fields in database , using exception converter convert sql server exception 1 application can handle.

public class sqlserverexceptionconverter : isqlexceptionconverter {     public exception convert(adoexceptioncontextinfo adoexceptioncontextinfo)     {         var sqlexception = adoexceptioncontextinfo.sqlexception sqlexception;         if (sqlexception != null)         {             // 2601 unique key, 2627 unique index; same thing:              // http://blog.sqlauthority.com/2007/04/26/sql-server-difference-between-unique-index-vs-unique-constraint/             if (sqlexception.number == 2601 || sqlexception.number == 2627)             {                 // custom exception                 return new uniquekeyexception(sqlexception.message, sqlexception);             }         }         return adoexceptioncontextinfo.sqlexception;     } } 

another approach can think of query database matching record before insert that's not foolproof because record inserted between select , insert.