Sorry for bothering, have met a problem I can not resolve by myself. I think the main reason - because I don't quite understand the way NHibernate works with Collections, but, documentation is readed from the beginning to the top. May be I have missed smth because of my English. Not quite sure.
My main problem is that I have not found a good source to read from about the way objects are handled by NHibernate. I am really new with ORM, so it is really hard form me.


The problem: Lazy Fetching or Mapping and Object initializing... not quite sure.

Mapping documents:
Assigment.hbm.xml
Trip.hbm.xml
Person.hbm.xml


I have 2 instances: Person and Trip. Their association is many-to-many, but, I need to have some additional properties of association so I have additional Table Assigment.
Here are my mappings:


Person.hbm.xml





Trip.hbm.xml



Assigment.hbm.xml


I have gotten 1000s of errors, but, after resolving all of them, I got the next one:

Full stack trace of any exception that occurs:
[SqlException (0x80131904): Cannot insert the value NULL into column 'person_email', table 'TripInviteDB.dbo.assigments'; column does not allow nulls. UPDATE fails.
The statement has been terminated.]
System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection) +862234
System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection) +739110
System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj) +188
System.Data.SqlClient.TdsParser.Run(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj) +1956
System.Data.SqlClient.SqlCommand.FinishExecuteReader(SqlDataReader ds, RunBehavior runBehavior, String resetOptionsString) +149
System.Data.SqlClient.SqlCommand.RunExecuteReaderTds(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, Boolean async) +903
System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, DbAsyncResult result) +132
System.Data.SqlClient.SqlCommand.InternalExecuteNonQuery(DbAsyncResult result, String methodName, Boolean sendToPipe) +415
System.Data.SqlClient.SqlCommand.ExecuteNonQuery() +135
NHibernate.Impl.BatcherImpl.ExecuteNonQuery(IDbCommand cmd) +29
NHibernate.Persister.Collection.AbstractCollectionPersister.Remove(Object id, ISessionImplementor session) +380

[ADOException: could not delete collection: [Model.Person.Assigments#fly_fuzz@tut.by]]
NHibernate.Persister.Collection.AbstractCollectionPersister.Remove(Object id, ISessionImplementor session) +553
NHibernate.Impl.ScheduledCollectionRemove.Execute() +32
NHibernate.Impl.SessionImpl.Execute(IExecutable executable) +112
NHibernate.Impl.SessionImpl.ExecuteAll(IList list) +72
NHibernate.Impl.SessionImpl.Execute() +198
NHibernate.Impl.SessionImpl.Flush() +42
NHibernate.Transaction.AdoTransaction.Commit() +160
TripInviteControl.saveOrUpdate(Object o) in C:\Sites\TripInviteASPDev\App_Code\TripInviteControl.cs:159
register_permissions.Next4_Click(Object sender, ImageClickEventArgs e) in C:\Sites\TripInviteASPDev\register_permissions.aspx.cs:75
System.Web.UI.WebControls.ImageButton.OnClick(ImageClickEventArgs e) +105
System.Web.UI.WebControls.ImageButton.RaisePostBackEvent(String eventArgument) +115
System.Web.UI.WebControls.ImageButton.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) +7
System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +11
System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) +33
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +5102




Here is the code I use to work with my objects.



And another thing I don't understand, why the testing code, which is


works just fine ???
But, if I don't handle the

and just p.Assigments.Add(assigment) I got a lazy fetching exception?


I am really lost. Appreciate any help.
Thank you for reading.
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I don't know where to look for. Don't have ability to buy one from Amazon.

Thanks for a well-formatted question.

It looks like two problems. The first (NULL FK error) is related to a poorly set up bidirectional association. You have cascades going both directions from Person and Trip. It kind of looks like you have a Parent-Child relationship from both to your assignment class, in which case you'll need to invert the collections (use inverse="true" on your set mappings). You might also investigate managing the association objects as part of a
composite-element on either Person or Trip (if that makes sense in your domain model).

The lazy initialization error is happening on add because a set needs to be able to compare the new addition to existing elements, since a new one can be added only once. This requires the collection to be loaded, possibly lazily. You are getting the exception because the session the Person was loaded in has been closed. Your workaround is pretty ugly, since exception handling is very expensive, and adding a new collection instead of loading the existing one could mess with existing children.

There are several options: keep the session open so that the lazy loading functions, eagerly fetch the collection at load time, or use a bag instead (which doesn't need to be loaded on Add() operations). For collection behavior, http://www.hibernate.org/hib_docs/nhibe ... ollections and http://www.hibernate.org/hib_docs/nhibe ... tions.html