Intoduction to NHibernate

Agenda Overview of NHibernate Models and Mappings Configuration Sessions and Transactions Queries

What is Nhibernate ? mature, ORM solution for.NET platform free, GNU Lesser General Public License mapping an object-oriented domain model to a relational database home == nhforge.orgnhforge.org files on sourceforgesourceforge groups Commercial support –hibernating rhinos - Ayende Rahienhibernating rhinos - Ayende Rahien –imeta - Steve Strong, Fabio Mauloimeta - Steve Strong, Fabio Maulo

History started as port of the popular Java O/R mapper Hibernate to.NET Hibernate was started in 2001 by Gavin King NHibernate was started around 2003 –ver 1.0 mirrored the feature set of Hibernate 2.1 –ver 1.2.1, released in 11/2007, features from Hibernate 3 and support for.NET 2.0, stored procedures, generics, and nullable types –ver 2.0 was released 08/2008. Comparable to Hibernate 3.2..NET 1.1 –ver December 04, NET 3.5. LINQ support, strongly typed criteria-like API called QueryOver, new AST- based parser for NHibernate's HQL,... –

Mappings mapping a class with XML –Keys, ID generators table-per-class hierarchy table per class table per concrete class one-to-many relationship –lazy loading collections, lazy loading proxies setting up a base entity class handling versioning and concurrency

bidirectional one-to-many class relationships mappings enumerations

mapping a class with XML 2x.xsd – intellisense mapping file - XML - extension.hbm.xml set Build Action to Embedded Resource !!! model - collection of classes that will be persisted in the database persistent class - any class that will be persisted (e.g. Person, Address) entity class - a persistent class with an ID

entity - an instance of an entity class POCO - Plain Old CLR Object –POCOs are objects not burdened with inheritance or attributes needed for specific frameworks all entity classes should be persistence ignorant –strongly held design decisions in NHibernate Id property - primary key value from the db persistent object identifier (POID)

Approaches to begin developing an NH application model-first –create model -> map the model -> generate our database tables from the model and mappings configuration-first database-first

Non-insert POID generators assign an identity to a persistent object without writing the object's data to the db hilo guid guid.comb guid.native uuid.hex, uuid.string counter, increment sequence, seqhilo

Post-insert POID generators require data to be persisted to the database for an ID to be generated - strongly discouraged identity select (uses natural id) sequence-identity trigger-identity native

table-per-class hierarchy data for our entire hierarchy is stored in a single table discriminator column ProductType –distinguish among products, books, and movies –by default, the contains the class name –Eg.Core.Product, Eg.Core.Book, or Eg.Core.Movie subclass properties as must be nullable suggested method for mapping class hierarchies

table-per-class properties of the base class in a shared table each subclass gets its own table joined-subclass element –key element to name the primary key column

table-per-concrete class each class gets its own table containing columns for all properties of the class and the base class there is no duplication of data union-subclass element

one-to-many relationship relate one entity to another

Lazy loading collections data isn't loaded from the database until it is required by the application 1.fetch Movie (Id, Name, Description, UnitPrice, and Director, but no Actors) 2.creates an instance of the Movie object 3.sets the properties of the Movie object with the data from the db 4.creates a special lazy loading object that implements IList, and sets the Actors property 5.returns Movie

foreach (var actor in movie.Actors) Console.WriteLine(actor.Actor); lazy loading object is initialized loads the associated ActorRole data disable lazy loading by adding the attribute lazy="false" to the list element

Lazy loading proxies supports lazy loading through the use of proxy objects public class ActorRole : Entity { public virtual string Actor { get; set; } public virtual string Role { get; set; } public virtual Movie Movie { get; set; } } proxy object is a subclass of Movie – requirements Movie cannot be a sealed class Movie must have a protected or public constructor without parameters All public members of Movie must be virtual. This includes methods

choices for the creation of these proxy objects –traditional choice DynamicProxy, part of the Castle –LinFu –Spring.NET –build your own lazy="false" on the class element of our Movie mapping to disable

Collections DuplicatesOrderType BagYesNoIList SetNo Iesi.Collections.ISet ListYes IList Map (Dictionary)Keys unique, Values noNoIDictionary most common types all collections may also use the ICollection type custom NHibernate.UserType.IuserCollection

Setting up a base entity class NH relies on the Equals() to determine equality application should not be aware of proxy objects Product instance with an ID of 8 should be equal to a different Product instance or Product proxy with an ID of 8 transient object is an object that has not been persisted to the db

Versioning and concurrency optimistic and pessimistic concurrency version element UPDATE Product SET Version = 2 */, Name = 'Junk' */, Description = 'Cool' */, UnitPrice = 100 */ WHERE Id = '764de11e-1fd0-491e db8015f9be5' */ AND Version = 1 */ If no rows updated StaleStateException the entity in memory is stale, or out of sync with the db

DateTime-based version fields –Datetime, DateTime2, timestamp attribute optimistic-lock –

Other mappings options Fluent Nhibernate public ProductMapping() { Id(p => p.Id).GeneratedBy.GuidComb(); DiscriminateSubClassesOnColumn("ProductType"); Version(p => p.Version); NaturalId().Not.ReadOnly().Property(p => p.Name); Map(p => p.Description); Map(p => p.UnitPrice).Not.Nullable(); }

ConfORM –convention-based mappings –mapper outputs an HbmMapping object built from our conventions –ConfORM uses conventions and patterns to build a mapping directly from the model –Customizable

Bidirectional one-to-many class relationships ORMs are designed to overcome the impedance mismatch between the object model and the relational model inverse attribute - determine which end of the relationship controls the foreign key we must keep both sides of relationship in sync

Mappings enumerations improperly mapped enumeration can lead to unnecessary updates by default, NH will map an enumeration to an int –AcctType = AccountTypes.Corporate –AcctType database field = 2 –int doesn't describe the business meaning store the name of the enumeration value –AcctType database field „Corporate“ type attribute –we tell NHibernate to use a custom class for conversion between.NET types and the database

Configuring NHibernate with App.config proxyfactory.factory_class –specifies the proxy framework we'll use dialect –specifies a dialect class that NHibernate uses to build SQL syntax connection.connection_string_name –references our connection string adonet.batch_size –group SQL DML statements in a single ADO.NET command mapping - where NHwill search for our mappings

components of NH app session represents a unit of work –NH session tracks changes to entities and writes those changes back to the database all at once –transactional write-behind

Dialects and drivers Microsoft SQL Server –CE, 7, 2000, 2005, 2008 Oracle –Lite, 8i, 9i, 10g MySql –MySql, MySql5 PostgreSQL, DB2, Informix, Sybase, Firebird, SQLite, Ingres

Configuring NHibernate with hibernate.cfg.xml separate xml configuration file