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• NHibernate lazy properties behavior?

  - by GeReV

  I've been trying to get NHibernate into development for a project I'm working on at my workplace. Since I have to put a strong emphasis on performance, I've been running a proof-of-concept stress test on an existing project's table with thousands of records, all of which contain a large text column. However, when selecting a collection of these records, the select statement takes a relatively long time to execute; apparently due to the aforementioned column. The first solution that comes to mind is setting this property as lazy: <property name="Content" lazy="true"/> But there seems to be no difference in the SQL generated by NHibernate. My question is, how do lazy properties behave in NHibernate? Is there some kind of type limitations I could be missing? Should I take a different approach altogether? Using HQL's new Class(column1, column2) approach works, but lazy properties sounds like a simpler solution. It's perhaps worth mentioning I'm using NHibernate 2.1.2GA with the Castle DynamicProxy. Thanks!

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• NHibernate not dropping foreign key constraints.

  - by Kendrick

  I'm new to NHibernate, so this is probably my mistake, but when I use: schema.Create(true, true); I get: SchemaExport [(null)]- There is already an object named 'XXX' in the database. System.Data.SqlClient.SqlException: There is already an object named 'XXX' in the database. I grabbed the SQL code nHibernate was using, ran it directly from MSSMS, and recieved similar errors. Looking into it, the generated code is not properly dropping the foreign key constraints. The drop looks like this: if exists (select 1 from sysobjects where id = OBJECT_ID(N'dbo[FK22212EAFBFE4C58]') AND parent_obj = OBJECT_ID('YYY')) alter table dbo.YYY drop constraint FK22212EAFBFE4C58 Doing a "select OBJECT_ID(N'dbo[FK22212EAFBFE4C58]')" I get null. If I take out the "dbo" (i.e. "select OBJECT_ID(N'[FK22212EAFBFE4C58]')") then the ID is returned. So, my question is, why is nHibernate adding the dbo, and why does that prevent the object from being returned (since the table owning the constraint is dbo.XXX) One of my mapping files: <?xml version="1.0" encoding="utf-8"?> <hibernate-mapping namespace="CanineApp.Model" assembly="CanineApp.Model" xmlns="urn:nhibernate-mapping-2.2"> <class name="MedicalLog" table="MedicalLog" schema="dbo"> <id name="MedicalLogID" type="Int64"> <generator class="identity" /> </id> <property name="InvoiceAmount" type="Decimal" not-null="true" /> ... <many-to-one name="Canine" class="Canine" column="CanineID" not-null="true" fetch="join" /> <many-to-one name="TreatmentCategory" class="TreatmentCategory" column="TreatmentCategoryID" not-null="true" access="field.camelcase-underscore" /> </class> </hibernate-mapping>

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• Fluent NHibernate AutoMap

  - by Markus

  Hi. I have a qouestion regarding the AutoMap xml generation. I have two classes: public class User { virtual public Guid Id { get; private set; } virtual public String Name { get; set; } virtual public String Email { get; set; } virtual public String Password { get; set; } virtual public IList<OpenID> OpenIDs { get; set; } } public class OpenID { virtual public Guid Id { get; private set; } virtual public String Provider { get; set; } virtual public String Ticket { get; set; } virtual public User User { get; set; } } The generated sequences of xml files are: For User class: <bag name="OpenIDs"> <key> <column name="User_Id" /> </key> <one-to-many class="BL_DAL.Entities.OpenID, BL_DAL, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" /> </bag> For OpenID class: <many-to-one class="BL_DAL.Entities.User, BL_DAL, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" name="User"> <column name="User_id" /> </many-to-one> I don't see the inverse=true attribute for the User mapping. Is it a normal behavior, or I made a mistake somewhere?

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• Fluent NHibernate Mapping and Formulas/DatePart

  - by Alessandro Di Lello

  Hi There, i have a very simple table with a Datetime column and i have this mapping in my domain object. MyDate is the name of the datetime column in the DB. public virtual int Day { get; set; } public virtual int Month { get; set; } public virtual int Year { get; set; } public virtual int Hour { get; set; } public virtual int Minutes { get; set; } public virtual int Seconds { get;set; } public virtual int WeekNo { get; set; } Map(x => x.Day).Formula("DATEPART(day, Datetime)"); Map(x => x.Month).Formula("DATEPART(month, Datetime)"); Map(x => x.Year).Formula("DATEPART(year, Datetime)"); Map(x => x.Hour).Formula("DATEPART(hour, Datetime)"); Map(x => x.Minutes).Formula("DATEPART(minute, Datetime)"); Map(x => x.Seconds).Formula("DATEPART(second, Datetime)"); Map(x => x.WeekNo).Formula("DATEPART(week, Datetime)"); This is working all great .... but Week Datepart. I saw with NHProf the sql generating for a select and here's the problem it's generating all the sql correctly but for week datepart.. this is part of the SQL generated: ....Datepart(day, MyDate) ... ....Datepart(month, MyDate) ... ....Datepart(year, MyDate) ... ....Datepart(hour, MyDate) ... ....Datepart(minute, MyDate) ... ....Datepart(second, MyDate) ... ....Datepart(this_.week, MyDate) ... where this_ is the alias for the table that nhibernate uses. so it's treating the week keyword for the datepart stuff as a column or something like that. To clarify there's no column or properties that is called week. some help ? cheers Alessandro

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• Mapping tables from an existing database to an object -- is Hibernate suited?

  - by Bernhard V

  Hello! I've got some tables in an existing database and I want to map them to a Java object. Actually it's one table that contains the main information an some other tables that reference to such a table entry with a foreign key. I don't want to store objects in the database, I only want to read from it. The program should not be allowed to apply any changes to the underlying database. Currently I read from the database with 5 JDBC sql queries and set the results then on an object. I'm now looking for a less code intensive way. Another goal is the learning aspect. Is Hibernate suitable for this task, or is there another ORM framework that better fits my requirement?

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• Fluent NHibernate - subclasses with shared reference

  - by ollie

  Edit: changed class names. I'm using Fluent NHibernate (v 1.0.0.614) automapping on the following set of classes (where Entity is the base class provided in the S#arp Architecture framework): public class Car : Entity { public virtual int ModelYear { get; set; } public virtual Company Manufacturer { get; set; } } public class Sedan : Car { public virtual bool WonSedanOfYear { get; set; } } public class Company : Entity { public virtual IList<Sedan> Sedans { get; set; } } This results in the following Configuration (as written to hbm.xml): <class name="Company" table="Companies"> <id name="Id" type="System.Int32" unsaved-value="0"> <column name="`ID`" /> <generator class="identity" /> </id> <bag cascade="all" inverse="true" name="Sedans" mutable="true"> <key> <column name="`CompanyID`" /> </key> <one-to-many class="Sedan" /> </bag> </class> <class name="Car" table="Cars"> <id name="Id" type="System.Int32" unsaved-value="0"> <column name="`ID`" /> <generator class="identity" /> </id> <property name="ModelYear" type="System.Int32"> <column name="`ModelYear`" /> </property> <many-to-one cascade="save-update" class="Company" name="Manufacturer"> <column name="`CompanyID`" /> </many-to-one> <joined-subclass name="Sedan"> <key> <column name="`CarID`" /> </key> <property name="WonSedanOfYear" type="System.Boolean"> <column name="`WonSedanOfYear`" /> </property> </joined-subclass> </class> So far so good! But now comes the ugly part. The generated database tables: Table: Companies Columns: ID (PK, int, not null) Table: Cars Columns: ID (PK, int, not null) ModelYear (int, null) CompanyID (FK, int, null) Table: Sedan Columns: CarID (PK, FK, int, not null) WonSedanOfYear (bit, null) CompanyID (FK, int, null) Instead of one FK for Company, I get two! How can I ensure I only get one FK for Company? Override the automapping? Put a convention in place? Or is this a bug? Your thoughts are appreciated.

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• How to save a large nhibernate collection without causing OutOfMemoryException

  - by Michael Hedgpeth

  How do I save a large collection with NHibernate which has elements that surpass the amount of memory allowed for the process? I am trying to save a Video object with nhibernate which has a large number of Screenshots (see below for code). Each Screenshot contains a byte[], so after nhibernate tries to save 10,000 or so records at once, an OutOfMemoryException is thrown. Normally I would try to break up the save and flush the session after every 500 or so records, but in this case, I need to save the collection because it automatically saves the SortOrder and VideoId for me (without the Screenshot having to know that it was a part of a Video). What is the best approach given my situation? Is there a way to break up this save without forcing the Screenshot to have knowledge of its parent Video? For your reference, here is the code from the simple sample I created: public class Video { public long Id { get; set; } public string Name { get; set; } public Video() { Screenshots = new ArrayList(); } public IList Screenshots { get; set; } } public class Screenshot { public long Id { get; set; } public byte[] Data { get; set; } } And mappings: <?xml version="1.0" encoding="utf-8" ?> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="SavingScreenshotsTrial" namespace="SavingScreenshotsTrial" default-access="property"> <class name="Screenshot" lazy="false"> <id name="Id" type="Int64"> <generator class="hilo"/> </id> <property name="Data" column="Data" type="BinaryBlob" length="2147483647" not-null="true" /> </class> </hibernate-mapping> <?xml version="1.0" encoding="utf-8" ?> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="SavingScreenshotsTrial" namespace="SavingScreenshotsTrial" > <class name="Video" lazy="false" table="Video" discriminator-value="0" abstract="true"> <id name="Id" type="Int64" access="property"> <generator class="hilo"/> </id> <property name="Name" /> <list name="Screenshots" cascade="all-delete-orphan" lazy="false"> <key column="VideoId" /> <index column="SortOrder" /> <one-to-many class="Screenshot" /> </list> </class> </hibernate-mapping> When I try to save a Video with 10000 screenshots, it throws an OutOfMemoryException. Here is the code I'm using: using (var session = CreateSession()) { Video video = new Video(); for (int i = 0; i < 10000; i++) { video.Screenshots.Add(new Screenshot() {Data = camera.TakeScreenshot(resolution)}); } session.SaveOrUpdate(video); }

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• NHibernate child deletion problem.

  - by JMSA

  Suppose, I have saved some permissions in the database by using this code: RoleRepository roleRep = new RoleRepository(); Role role = new Role(); role.PermissionItems = Permission.GetList(); roleRep .SaveOrUpdate(role); Now, I need this code to delete the PermissionItem(s) associated with a Role when role.PermissionItems == null. Here is the code: RoleRepository roleRep = new RoleRepository(); Role role = roleRep.Get(roleId); role.PermissionItems = null; roleRep .SaveOrUpdate(role); But this is not happening. What should be the correct way to cope with this situation? What/how should I change, hbm-file or persistance code? Role.cs public class Role { public virtual string RoleName { get; set; } public virtual bool IsActive { get; set; } public virtual IList<Permission> PermissionItems { get; set; } } Role.hbm.xml <?xml version="1.0" encoding="utf-8" ?> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="POCO" namespace="POCO"> <class name="Role" table="Role"> <id name="ID" column="ID"> <generator class="native" /> </id> <property name="RoleName" column="RoleName" /> <property name="IsActive" column="IsActive" type="System.Boolean" /> <bag name="PermissionItems" table="Permission" cascade="all" inverse="true"> <key column="RoleID"/> <one-to-many class="Permission" /> </bag> </class> </hibernate-mapping> Permission.cs public class Permission { public virtual string MenuItemKey { get; set; } public virtual int RoleID { get; set; } public virtual Role Role { get; set; } } Permission.hbm.xml <?xml version="1.0" encoding="utf-8" ?> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="POCO" namespace="POCO"> <class name="Permission" table="Permission"> <id name="ID" column="ID"> <generator class="native"/> </id> <property name="MenuItemKey" column="MenuItemKey" /> <property name="RoleID" column="RoleID" /> <many-to-one name="Role" column="RoleID" not-null="true" cascade="all"> </many-to-one> </class> </hibernate-mapping>

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• NHibernate Session Management Advice

  - by Hugusta

  I need some advice on NHibernate Session Management for a C# WinForms application. I am currently porting an application to use NHibernate. I am also employing a UnitOfWork pattern as described in the link below; http://nhforge.org/wikis/patternsandpractices/nhibernate-and-the-unit-of-work-pattern.aspx My question relates to Sessions. Can you only have one session running per thread at all times? I have a scenario in which a Session (UnitOfWork) may be open for a form shown by the application but the user opens another form (i.e. Tools - Options) which I would like to have its own UnitOfWork. Clearly in this instance it would make more sense to open another Session for the "Tools - Options" form and not use the currently open session for the underlying form. Can we have a Dictionary of Sessions on the one thread? Any advice on session management is appreciated.

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• NHibernate's automatic (dirty checking) update behaviour - turning it off

  - by Andrew Bullock

  I've just discovered that if I get an object from an NHibernate session and change a property on object, NHibernate will automatically update the object on commit without me calling Session.Update(myObj)! I can see how this could be helpful, but as default behaviour it seems crazy! How can I stop this happening? Is this default NHib behaviour or something coming from Fluent NHibs AutoPersistenceModel? If there's no way to stop this, what do I do? Unless I'm missing the point this behaviour seems to create a right mess, violating my UoW. Im using NHibernate 2.0.1.4 and a Fluent NHib build from 18/3/2009 Edit, is this guy right with his answer? Edit: I've also read that overriding an Event Listener could be a solution to this. However, IDirtyCheckEventListener.OnDirtyCheck isn't called in this situation. Does anyone know which listener I need to override? Thanks Andrew

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• How does NHibernate handle cascade="all-delete-orphan"?

  - by Johannes Rudolph

  I've been digging around the NHibernate sources a little, trying to understand how NHibernate implements removing child elements from a collection. I think I've already found the answer, but I'd ideally like this to be confirmed by someone familiar with the matter. So far I've found AbstractPersistentCollection (base class for all collection proxies) has a static helper method called GetOrphans to find orphans by comparing the current collection with a snapshot. The existence of this method suggests NHibernate tries to find all oprhaned elements and then deletes them by key. Is this correct, in terms of the generated SQL?

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• MVC nhibernate entiry mapping for dropdown list

  - by Rod McLeay

  Hi, I have a dropdown list on an ASP.NET MVC project that I am pretty sure is not binding to my model because of my nhibernate mapping. I have tried many variations on the asp mvc side resulting in this post here. MVC side of things seems fine I believe the issue may be that my object is trying to bind, but my mapping is out of whack. My mapping is: <many-to-one name="Project" lazy="false" class="AgileThought.ERP.Domain.Property.Project" column="ProjectGUID" /> My View gives an error saying that the GUID from the dropdownList selected value is not valid. Which I think may be that it is trying to push the GUID into my related project object. The value 'fd38c877-706f-431d-b624-1269184eeeb5' is invalid. My related project list binds to the dropdown list just fine, it is just not binding to my models Project entity. Does the related Project entity need to know about its relationship? Its really just a lookup list. Many thanks for your time and best regards, Rod

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• Is Lazy Loading required for nHibernate?

  - by johnny

  It took me a long time but I finally got nHibernate's Hello World to work. It worked after I did "lazy loading." Honestly, I couldn't tell you why it all worked, but it did and now I am reading you don't need lazy loading. Is there a hello world that anyone has that is bare bones making nHibernate work? Do you have to have lazy loading? I ask because I would like to use nHibernate but I need to understand how things are working. Thank you. Do you know of a hello world that doesn't have so much overhead? Is it better to use lazy loading? EDIT: I am using asp.net 3.5. Web Application Project.

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• Nhibernate criteria query inserts an extra order by expression when using JoinType.LeftOuterJoin and Projections

  - by Aaron Palmer

  Why would this nhibernate criteria query produce the sql query below? return Session.CreateCriteria(typeof(FundingCategory), "fc") .CreateCriteria("FundingPrograms", "fp") .CreateCriteria("Projects", "p", JoinType.LeftOuterJoin) .Add(Restrictions.Disjunction() .Add(Restrictions.Eq("fp.Recipient.Id", recipientId)) .Add(Restrictions.Eq("p.Recipient.Id", recipientId)) ) .SetProjection(Projections.ProjectionList() .Add(Projections.GroupProperty("fc.Name"), "fcn") .Add(Projections.Sum("fp.ObligatedAmount"), "fpo") .Add(Projections.Sum("p.ObligatedAmount"), "po") ) .AddOrder(Order.Desc("fpo")) .AddOrder(Order.Desc("po")) .AddOrder(Order.Asc("fcn")) .List<object[]>(); SELECT this_.Name as y0_, sum(fp1_.ObligatedAmount) as y1_, sum(p2_.ObligatedAmount) as y2_ FROM fundingCategories this_ inner join fundingPrograms fp1_ on this_.fundingCategoryId = fp1_.fundingCategoryId left outer join projects p2_ on fp1_.fundingProgramId = p2_.fundingProgramId WHERE (fp1_.recipientId = 6 /* @p0 */ or p2_.recipientId = 6 /* @p1 */) GROUP BY this_.Name ORDER BY p2_.name asc, y1_ desc, y2_ desc, y0_ asc It is incorrectly putting the p2_name asc into the ORDER BY statement, and causing it to crash. This only happens when I use JoinType.LeftOuterJoin on my Projects criteria. Is this a known nhibernate bug? I'm using nhibernate 2.0.1.4000. Thanks for any insight.

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• Use a folder of xml files as data source for nhibernate

  - by Bart Van Eyndhoven

  I'm going to start writing NUnit tests for a few classes in my project. A certain number of these classes use data gathered through nhibernate from a sql server 2008 database. The part of the program I'm about to test is very specific (and complicated). Therefore I have made a folder of xml files. Combined, the xml files could result in the database structure. I mean each xml file corresponds to a table in the database. The data in the xml files is also consistent with the database. Is there a way to use this folder of xml files as data source for nhibernate? I mean: can I use nhibernate to gather my test data (wich I have specifically chosen) instead of data from the database? In this way, I could usefully test this component without corrrupting the (test) database for future tests.

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• NHibernate Linq queries not returning data saved in the same transaction

  - by Andrew

  Hi, I have a situation where I am using NHibernate in a WCF service and using a TransactionScope for the transaction management. NHibernate enlists in the ambient transaction fine, but, any changes I make and save inside the transaction, are not visible to any queries I make while still in that transaction. So if I add an entity and session.save() it, then further on in the code, there is a linq query against that entities table, the entity I just added is not returned. Strangely this seems to work fine if I use explicit NHibernate transactions in my tests. Anyone have any ideas as to why and what I can do about it? Many thanks Andrew

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• Loading tables dynamically with NHibernate

  - by Trevor Goertzen

  I'm working on a project that requires me to load tables based on table names stored in another table. More tables will be added to the DB (and by someone else), so creating NHibernate mapping files for each table isn't an option. Does anyone know if it is possible to load tables dynamically using NHibernate? Edit: I should add that I'm on .NET 2.0, so I can't use Fluent NHibernate. Thanks for the suggestion though guys. I will use that as evidence in convincing my associates to upgrade.

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• NHibernate, each property is filled with a different select statement

  - by Eitan

  I'm retrieving a list of nhibernate entites which have relationships to other tables/entities. I've noticed instead of NHibernate performing JOINS and populating the properties, it retrieves the entity and then calls a select for each property. For example if a user can have many roles and I retrieve a user from the DB, Nhibernate retrieves the user and then populates the roles with another select statement. The problem is that I want to retrieve oh let's say a list of products which have various many-to-many relationships and relationships to items which have their own relationships. In the end I'm left with over a thousand DB calls to retrieve a list of 30 products. Thanks. I've also set default lazy loading to false because whenever I save the list of entities to a session, I get an error when trying to retrieve it on another page: LazyInitializationException: could not initialize proxy If anybody could shed any light I would truly appreciate it. Thanks. Eitan

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• NHibernate many-to-many mapping

  - by Scozzard

  Hi, I am having an issue with many-to-many mapping using NHibernate. Basically I have 2 classes in my object model (Scenario and Skill) mapping to three tables in my database (Scenario, Skill and ScenarioSkill). The ScenarioSkills table just holds the IDs of the SKill and Scenario table (SkillID, ScenarioID). In the object model a Scenario has a couple of general properties and a list of associated skills (IList) that is obtained from the ScenarioSkills table. There is no associated IList of Scenarios for the Skill object. The mapping from Scenario and Skill to ScenarioSkill is a many-to-many relationship: Scenario * --- * ScenarioSkill * --- * Skill I have mapped out the lists as bags as I believe this is the best option to use from what I have read. The mappings are as follows: Within the Scenario class <bag name="Skills" table="ScenarioSkills"> <key column="ScenarioID" foreign-key="FK_ScenarioSkill_ScenarioID"/> <many-to-many class="Domain.Skill, Domain" column="SkillID" /> </bag> And within the Skill class <bag name="Scenarios" table="ScenarioSkills" inverse="true" access="noop" cascade="all"> <key column="SkillID" foreign-key="FK_ScenarioSkill_SkillID" /> <many-to-many class="Domain.Scenario, Domain" column="ScenarioID" /> </bag> Everything works fine, except when I try to delete a skill, it cannot do so as there is a reference constraint on the SkillID column of the ScenarioSkill table. Can anyone help me? I am using NHibernate 2 on an C# asp.net 3.5 web application solution.

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• NHibernate 3 and MySQL setup tutorial

  - by ryanzec

  Since I have given up on using the entity framework 4 as my ORM (getting it to work with MySQL and mapping table/field names like this_table/this_field to object naming like ThisTable/ThisField is POCO) I am now looking at NHibernate as it seems the the next big well know ORM for C# that probably with not die off any time soon. I am trying to lookup some tutorials and a lot of them in the configuration section have 2-2 in it and was wondering if those configuration would work with NHibernate 3? I am just curious if the 2-2 refers to the version of NHibernate or something different.

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• How to test soft deletion event listner without setting up NHibernate Sessions

  - by isuruceanu

  I have overridden the default NHibernate DefaultDeleteEventListener according to this source: http://nhforge.org/blogs/nhibernate/archive/2008/09/06/soft-deletes.aspx so I have protected override void DeleteEntity( IEventSource session, object entity, EntityEntry entityEntry, bool isCascadeDeleteEnabled, IEntityPersister persister, ISet transientEntities) { if (entity is ISoftDeletable) { var e = (ISoftDeletable)entity; e.DateDeleted = DateTime.Now; CascadeBeforeDelete(session, persister, entity, entityEntry, transientEntities); CascadeAfterDelete(session, persister, entity, transientEntities); } else { base.DeleteEntity(session, entity, entityEntry, isCascadeDeleteEnabled, persister, transientEntities); } } How can I test only this piece of code, without configuring an NHIbernate Session?

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• How do I map nested generics in NHibernate

  - by Gluip

  In NHibernate you can map generics like this <class name="Units.Parameter`1[System.Int32], Units" table="parameter_int" > </class> But how can I map a class like this? Set<T> where T is a Parameter<int> like this Set<Parameter<int>> My mapping hbm.xml looking like this fails <class name="Set`1[[Units.Parameter`1[System.Int32], Units]],Units" table="settable"/> I simplified my mappings a little to get my point accross very clearly. Basically I want NHibernate to map generic class which has has generic type parameter. Want I understand from googling around is that NHibernate is not able to parse the name to the correct type in TypeNameParser.Parse() which result in the following error when adding the mapping to the configuration System.ArgumentException: Exception of type 'System.ArgumentException' was thrown. Parameter name: typeName@31 Anybody found a way around this limitation?

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• How to model a relationship that NHibernate (or Hibernate) doesn’t easily support

  - by MylesRip

  I have a situation in which the ideal relationship, I believe, would involve Value Object Inheritance. This is unfortunately not supported in NHibernate so any solution I come up with will be less than perfect. Let’s say that: “Item” entities have a “Location” that can be in one of multiple different formats. These formats are completely different with no overlapping fields. We will deal with each Location in the format that is provided in the data with no attempt to convert from one format to another. Each Item has exactly one Location. “SpecialItem” is a subtype of Item, however, that is unique in that it has exactly two Locations. “Group” entities aggregate Items. “LocationGroup” is as subtype of Group. LocationGroup also has a single Location that can be in any of the formats as described above. Although I’m interested in Items by Group, I’m also interested in being able to find all items with the same Location, regardless of which group they are in. I apologize for the number of stipulations listed above, but I’m afraid that simplifying it any further wouldn’t really reflect the difficulties of the situation. Here is how the above could be diagrammed: Mapping Dilemma Diagram: (http://www.freeimagehosting.net/uploads/592ad48b1a.jpg) (I tried placing the diagram inline, but Stack Overflow won't allow that until I have accumulated more points. I understand the reasoning behind it, but it is a bit inconvenient for now.) Hmmm... Apparently I can't have multiple links either. :-( Analyzing the above, I make the following observations: I treat Locations polymorphically, referring to the supertype rather than the subtype. Logically, Locations should be “Value Objects” rather than entities since it is meaningless to differentiate between two Location objects that have all the same values. Thus equality between Locations should be based on field comparisons, not identifiers. Also, value objects should be immutable and shared references should not be allowed. Using NHibernate (or Hibernate) one would typically map value objects using the “component” keyword which would cause the fields of the class to be mapped directly into the database table that represents the containing class. Put another way, there would not be a separate “Locations” table in the database (and Locations would therefore have no identifiers). NHibernate (or Hibernate) do not currently support inheritance for value objects. My choices as I see them are: Ignore the fact that Locations should be value objects and map them as entities. This would take care of the inheritance mapping issues since NHibernate supports entity inheritance. The downside is that I then have to deal with aliasing issues. (Meaning that if multiple objects share a reference to the same Location, then changing values for one object’s Location would cause the location to change for other objects that share the reference the same Location record.) I want to avoid this if possible. Another downside is that entities are typically compared by their IDs. This would mean that two Location objects would be considered not equal even if the values of all their fields are the same. This would be invalid and unacceptable from the business perspective. Flatten Locations into a single class so that there are no longer inheritance relationships for Locations. This would allow Locations to be treated as value objects which could easily be handled by using “component” mapping in NHibernate. The downside in this case would be that the domain model becomes weaker, more fragile and less maintainable. Do some “creative” mapping in the hbm files in order to force Location fields to be mapped into the containing entities’ tables without using the “component” keyword. This approach is described by Colin Jack here. My situation is more complicated than the one he describes due to the fact that SpecialItem has a second Location and the fact that a different entity, LocatedGroup, also has Locations. I could probably get it to work, but the mappings would be non-intuitive and therefore hard to understand and maintain by other developers in the future. Also, I suspect that these tricky mappings would likely not be possible using Fluent NHibernate so I would use the advantages of using that tool, at least in that situation. Surely others out there have run into similar situations. I’m hoping someone who has “been there, done that” can share some wisdom. :-) So here’s the question… Which approach should be preferred in this situation? Why?

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• Is it worth migrating to NHibernate 2.x from NHibernate 1.2?

  - by Amitabh

  We are using nHibernate 1.2 in a system which is not performing good. Will there be some performance improvement if we migrate to latest version of nHibernate? Overall is it a good idea to migrate to the latest version of nHibernate? EDIT: I want to use following features to improve performance. 1. Second level cache. 2. Joined Table. 3. MultiQuery to batch queries.

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• nhibernate subclass in code

  - by Antonio Nakic Alfirevic

  I would like to set up table-per-classhierarchy inheritance in nhibernate thru code. Everything else is set in XML mapping files except the subclasses. If i up the subclasses in xml all is well, but not from code. This is the code i use - my concrete subclass never gets created:( //the call NHibernate.Cfg.Configuration config = new NHibernate.Cfg.Configuration(); SetSubclass(config, typeof(TAction), typeof(tActionSub1), "Procedure"); //the method public static void SetSubclass(Configuration configuration, Type baseClass, Type subClass, string discriminatorValue) { PersistentClass persBaseClass = configuration.ClassMappings.Where(cm => cm.MappedClass == baseClass).Single(); SingleTableSubclass persSubClass = new SingleTableSubclass(persBaseClass); persSubClass.ClassName = subClass.AssemblyQualifiedName; persSubClass.DiscriminatorValue = discriminatorValue; persSubClass.EntityPersisterClass = typeof(SingleTableEntityPersister); persSubClass.ProxyInterfaceName = (subClass).AssemblyQualifiedName; persSubClass.NodeName = subClass.Name; persSubClass.EntityName = subClass.FullName; persBaseClass.AddSubclass(persSubClass); } the Xml mapping looks like this: <?xml version="1.0" encoding="utf-8" ?> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" namespace="Riz.Pcm.Domain.BusinessObjects" assembly="Riz.Pcm.Domain"> <class name="Riz.Pcm.Domain.BusinessObjects.TAction, Riz.Pcm.Domain" table="dbo.tAction" lazy="true"> <id name="Id" column="ID"> <generator class="guid" /> </id> <discriminator type="String" formula="(select jt.Name from TJobType jt where jt.Id=JobTypeId)" insert="true" force="false"/> <many-to-one name="Session" column="SessionID" class="TSession" /> <property name="Order" column="Order1" /> <property name="ProcessStart" column="ProcessStart" /> <property name="ProcessEnd" column="ProcessEnd" /> <property name="Status" column="Status" /> <many-to-one name="JobType" column="JobTypeID" class="TJobType" /> <many-to-one name="Unit" column="UnitID" class="TUnit" /> <bag name="TActionProperties" lazy="true" cascade="all-delete-orphan" inverse="true" > <key column="ActionID"></key> <one-to-many class="TActionProperty"></one-to-many> </bag> <!--<subclass name="Riz.Pcm.Domain.tActionSub" discriminator-value="ZPower"></subclass>--> </class> </hibernate-mapping> What am I doing wrong? I can't find any examples on google:(

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