Hi,

How can I tell NHibernate to explicitly get and object from the DataBase, and not from the cache?

For instance:
1. User A uses the object MyCompany with ID = 5.
2. User A stops using this object (MyCompany = Nothing)
3. User B opens MyCompany with ID = 5, makes changes to it, and saves it to the database.
4. User A uses again MyCompany 5, but doesn't get the changes that User B has made in the meantime!! Although: They need the updated object!


We're using the Get-method to retrieve the object (objSelected = SessionManager.Session.Get(Of T)(intID) )

Does anybody knows how to do this? Any help will be appreciated.

Thanks a lot in advance,


Pieter





Hibernate version: 1.2.0.4000

Mapping documents:
<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2">
<class name="Ghost.clsEntreprise, Ghost" table="tblEntreprises" dynamic-update="true" lazy="false">
<id name="EntrepriseID" column="EntrepriseID" type="Int32">
<generator class="identity" />
</id>
<property name="Nom" column="Nom" type="String" length="50" />
<property name="Compte" column="CompteBancaire" type="String" length="30" />
<property name="Iban" column="Iban" type="String" length="30" />
</class>
</hibernate-mapping>


Name and version of the database you are using: SQL 2005 SP2

Hi pieterc!

1) You have to create new (empty or clear) session to discard cache. Of course it will not help if you use second level cache.
2) You may use session.Refresh(probablyOutdatedObject) - to get "current state" from underlying DB. But it may fail if object was removed from DB... So you may want to use query (it will first check DB for existence of requested objects) to get object...

Hi,

Thanks you for your quick answer.

About the solutions:
1) Creating a new session: Won't this have a downside on the performance?

2) About the Refresh: Does this mean that, in case the object wasn't yet in the cache of NHibernate, NH will actually check two times to the DataBase (the first to to get it, the second time fot rhe Refresh).

Thanks a lot,

Pieter

For an IQuery or ICriteria, you can call SetForceCacheRefresh(true) to bypass the second level cache.

Hi pieterc!

AFAIK session creation is not so costly.
Moreover, extra large session (session having thousands of objects in its cache) will be really slow.
But main point is NHibernate session idiosyncrasy - it's exception intolerance - so you HAVE to close session in case of any error...

I'm not so experienced in NHibernate internal workflow, but I bet it doesn't hit DB twice while querying.
It will execute just one ADO.NET query, but it will process resultset items (result rows) differently - if object IS in session cache (seek by class and id) - NHibernate will return cached instance, if not - it will create one from resultset. At least it make sense :)

Agreed. Specifically, the doc says the following:
An ISession is an inexpensive, non-threadsafe object that should be used once, for a single business process, and then discarded

Pieter, you may want to read Chapter 10 of the docs. It deals with concurrency and whatnot.