Lviv .Net User Group. NHibernate

NHibernateby Andriy Buday

Outline Q1: What is NHibernate? Q2: Why do I need it? Q3: How does it look like?

Concepts DEMO 1: Hello World!

Q4: How can I proceed with it? Queries More about mapping, querying, usage patterns DEMO 2: Customer-Orders-Products

http://andriybuday.blogspot.com/

Let see… will we get what we want!

Q1: What is NHibernate?NHibernate is… ORM New level of Abstraction


Paradigm mismatch

Q2: Why Do I need it?Because…


Development speed increases Reducing database work Optimizes access to DB, so could even perform better

than plain ADO.NET You think in terms of business model, not database More time for real programming

Q2: Why Do I need it?Why do I like NHibernate?


Mature Free & Open Source Good community support Flexible

Allows you do Domain Driven Design You asked for comparison with other ORM…

LINQ to SQL doesn’t really lead you to good models Entity Framework has better Linq and it is Microsoft Visit http://ormbattle.net/ for performance numbers Google.Search(string.Format“Nhibernate vs. {0}”, yourORM);

http://ormbattle.net/

Q3: How does it look like?Concepts: Unit of Work


Kind of “workspace” within which you can do anything you want

A Unit Of Work either success or fails as a unit Conceptually like database transactions

In NHibernate we have ISession which does the same Conceptually we have the same for in ADO.NET as

DataSet

Q3: How does it look like?Concepts: ISession


Open a session We get it from the session factory

We do some work Session.Add(…) Session.Delete(…)

Commit the session Session.Flush(…)

Q3: How does it look like?Concepts: ISessionFactory


We are getting our session through this class Very expensive to create One per database or application

Q3: How does it look like?Concepts: Summary


Configuration Class builds Session Factory Session Factory builds Session Session is used as Unit Of Work to interaction with

objects and persist to underlying database

var sessionFactory = new Configuration().Configure().BuildSessionFactory();

using (var session = sessionFactory.OpenSession())

{

var customer = new Customer();

session.SaveOrUpdate(customer);

session.Flush();

}

Q3: How does it look like?Architecture: and look from inside?


Q3: How does it look like?DEMO: Hello World!


Just basics… to refresh our minds

Q4: How can I proceed with it? More on Query API


Criteria API Object oriented querying ICriteria chaining Easy to write Hard to read

HQL API String based Parameterized Similar to SQL Speak in terms of Objects More flexible

“from Customer c wherec.FirstName = :firstName”

session.CreateCriteria(typeof(Customer)) .Add(Restrictions.Eq("FirstName", "Hello"))

Q4: How can I proceed with it? Mapping


<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" default-lazy="true" assembly="LearningNHibernate" namespace="LearningNHibernate">

<class name="Customer" table="Customer" xmlns="urn:nhibernate-mapping-2.2">

<id name="CustomerId" column="CustomerId" type="Int32">

<generator class="identity" />

</id>

<property name="FirstName" column="Firstname" length="50" type="String">

<column name="Firstname" />

</property>

<property name="LastName" column="Lastname" length="50" type="String">

<column name="Lastname" />

</property>

</class>

</hibernate-mapping>

public class CustomerMap : ClassMap<Customer>

{

public CustomerMap()

{

WithTable("Customer");

Id(x => x.CustomerId);

Map(x => x.FirstName, "Firstname");

Map(x => x.LastName, "Lastname").WithLengthOf(50);

}

}

Q4: How can I proceed with it? Fetch strategies


Lazy loading Default for all collections Members are loaded from database when assessed Usually good for performance Session has to stay OPEN

Eager Fetching Use when you sure you’ll use data OUTER joins

Q4: How can I proceed with it? Caching, batching, concurrency


First level cache Following will run only one SELECT

Second level cache Within two sessions you still run one SELECT It is needed to explicitly turn it on everywhere

Batch processing <property name="adonet.batch_size">250</property>

Concurrency <version name="Version" column="Version"/>

var customer1 = session.Get<Customer>(5);

var customer2 = session.Get<Customer>(5);

Q4: How can I proceed with it?


Use FluentNhibernate to do not bore developers with XML

Create wrappers to have NHibernateRepository Implement UnitOfWork VS projects Two ways for kick-off

From database to Objects From objects to Database

DEMO 2: Mapping, Querying, LazyLoad, etc..


Damn it! Let’s write some code again!

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@andriybuday


http://dotnetug-lviv.blogspot.com/

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Links


My blog: http://andriybuday.blogspot.com

Lviv .NET User Group: http://dotnetug-lviv.blogspot.com/

NHibernate: Home Page: http://nhibernate.com/ Reference: http://www.nhforge.org/doc/nh/en/index.html

Great series of screencasts on NHibernate: http://www.summerofnhibernate.com/

ORM with NHibernate screen cast (2 hours) http://www.flux88.com/uploads/ORMWithNHibernateScreenCast.wmv

Tools: Profiler: http://nhprof.com/ Fluent NHibernate: http://fluentnhibernate.org/ MyGeneration: http://www.mygenerationsoftware.com/



http://nhibernate.com/

http://www.nhforge.org/doc/nh/en/index.html

http://www.summerofnhibernate.com/

http://www.flux88.com/uploads/ORMWithNHibernateScreenCast.wmv

http://nhprof.com/

http://fluentnhibernate.org/

http://www.mygenerationsoftware.com/

Technology

Lviv .Net User Group. NHibernate