Update uses previously autogenerated ID on Oracle - sql-server

Question

We're having a strange problem in Oracle. I'll sketch some (simplified) context first:
Consider this mapping to an Entity:
public EntityMap()
{
Table("EntityTable");
Id(x => x.Id)
.Column("entityID")
.GeneratedBy.Native("ENTITYID").UnsavedValue(0);
Map(x => x.SomeBoolean).Column("SomeBoolean");
}
and this code:
var entity = new Entity();
using (var transaction = new TransactionScope(TransactionScopeOption.Required))
{
Session.Save(entity);
transaction.Complete();
}
//A lot of code
if(someCondition)
{
using (var transaction = new TransactionScope(TransactionScopeOption.Required))
{
enitity.SomeBoolean = true;
Session.Update(entity);
transaction.Complete();
}
}
This code is called a few times. The first time it generates the following queries:
select ENTITYID.nextval from dual
INSERT INTO Entity
(SomeBoolean, EntityID)
VALUES (0, 1216)
UPDATE Entity
SET SomeBoolean = 1
WHERE EntityID = 1216
The second time it is called these queries are generated (someCondition is false)
select ENTITYID.nextval from dual
INSERT INTO Entity
(SomeBoolean, EntityID)
VALUES (0, 1217)
And now the trouble begins. From now on, each insert will use the correct autoincremented value, but the update will always use 1217
select ENTITYID.nextval from dual
INSERT INTO Entity
(SomeBoolean, EntityID)
VALUES (0, 1218)
UPDATE Entity
SET SomeBoolean = 1
WHERE EntityID = 1217
And of course, this is not what we want to happen. If I inspect the value of the Id while debugging, it contains the correct autoincremented value. Somehow, deep in the bowels of NHibernate, the incorrect is is assigned to the WHERE clause...
The strange part is that this only happens on Oracle. If I switch NHibernate to MsSql, everything works like a charm.

Answer 1

So I found out what happened. NHibernate changed it's default connection release mode between versions 1.x and 2.x. Instead of closing the connection when the session is Disposed, the connections is now closed after each transaction. However, we were manually coordinating our transactions which apparently caused troubles in Oracle.
This question has some extra information and this entry in the NHibernate documentation also clarifies how the connections are handeled:
As of NHibernate, if your application manages transactions through .NET APIs such as System.Transactions library, ConnectionReleaseMode.AfterTransaction may cause NHibernate to open and close several connections during one transaction, leading to unnecessary overhead and transaction promotion from local to distributed. Specifying ConnectionReleaseMode.OnClose will revert to the legacy behavior and prevent this problem from occuring.
This blog post is what got me looking in the right direction.