Configuring NHibernate in a Multiple Project Layout

I recently had to setup NHibernate in a multiple project c#, asp.net MVC solution. Since most of the tutorials and books only show a basic single project layout I thought I would post an example of how to configure NHiberate with a multi-project solution.

The main problem I had was that my model objects or entity objects were in a separate project than my database access code which contained the .hbm.xml mapping files. When I tried to configure NHibernate with the basic examples I was getting an “NHibernate.MappingException : No persister for: YourClass” exception. I was still getting that exception even after changing the .hbm.xml files to be an “Embedded Resource”. I finally figured out that my .hbm.xml files needed to reference the ModelLayer assebmly and my NHibernate.Cfg.Configuration.AddAssembly() needed to reference the DataAccessLayer assebmly. See screen shots and code examples below for more details.

Solution layout

Model objects Car.cs and CarLot.cs

using System.ComponentModel.DataAnnotations;
namespace MvcAgain.Models {
    public class Car {
        [Required]
        public virtual int Id {get; set;}
        [StringLength(35), Required]
        public virtual string Manufacturer {get; set;}
        [StringLength(35), Required]
        public virtual string Model {get; set;}
        public virtual CarLot Lot {get; set;}
    }
}//end of Car.cs

using Iesi.Collections;
using System.ComponentModel.DataAnnotations;
namespace MvcAgain.Models {
    public class CarLot {
        [Required]
        public virtual int Id { get; protected set; }
        [StringLength(35), Required]
        public virtual string Name { get; protected set; }
        public virtual ISet Cars { get; protected set; }
    }
}//end of CarLot.cs

Car.hbm.xml and CarLot.hbm.xml

These .hbm.xml files are in the DataAccessLayer project, but they reference the ModelLayer assembly.

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
                   assembly="ModelLayer"
                   namespace="MvcAgain.Models">
  <class name="MvcAgain.Models.Car" lazy="false" table="cars">
    <id name="Id">
      <generator class="native"/>
    </id>
    <property name="Model"/>
    <property name="Manufacturer"/>
    <many-to-one name="Lot" class="CarLot" column="lotid" not-null="true">
    </many-to-one>
  </class>
</hibernate-mapping>

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
                   assembly="ModelLayer"
                   namespace="MvcAgain.Models">
  <class name="MvcAgain.Models.CarLot" lazy="false" table="carlots">
    <id name="Id">
      <generator class="native"/>
    </id>
    <property name="Name"/>
    <set name="Cars" inverse="true">
        <key column="lotid"/>
        <one-to-many class="Car"/>
    </set>
  </class>
</hibernate-mapping>

NHibernateSessionFactory.cs (NHibernate configuration code)

using NHibernate.Cfg;
using NHibernate;
namespace MvcAgain.DataAccessLayer {

    public class NHibernateSessionFactory {

        private static ISessionFactory sessionFactory = null;

        private static ISessionFactory SessionFactory {
            get {
                if(sessionFactory == null) {
                    Configuration configuration = new Configuration();
                    configuration.Configure();
                    //note: you must use the name of the assembly
                    //that contains the .hbm.xml mapping files.
                    //For this example NHibernate will load all .hbm.xml files it
                    //finds in the DataAccessLayer assembly
                    configuration.AddAssembly("DataAccessLayer");
                    sessionFactory = configuration.BuildSessionFactory();
                }
                return sessionFactory;
            }
        }

        public static ISession OpenSession() {
            return SessionFactory.OpenSession();
        }
    }//end of class
}//end of namespace

ModelLayer assembly name in the properties pane.

ASP.Net MVC Book Review and musings

ASP.Net MVC musings

• ASP.Net MVC is a CoC MVC framework, it’s not a “full stack” framework. You still need to implement some type of database layer.
• Traditional ASP.net web forms attempts to hide the core parts of web development HTML, JS, CSS. ASP.Net MVC does not.
• Learning a pattern like MVC in web framework that allows developers to be aware of HTML, JS, CSS will only benefit you as a web developer.
  • If you actually understand how web pages work it makes you a better debugger and a more well rounded programmer. You are able to more easily apply your knowledge and skill set to other languages/platforms. I know that some web form developers do know the details of web development, but in my opinion most do not.
• The fact that ASP.Net MVC makes it easier to test will not appeal to people who have never written a unit test in their life. You have to convince such people by showing a real world example demonstrating how test coverage can save you loads of time and money in the maintenance phase of application development. But at that point you will only get architects and project managers to buy in, the lazy developers that fear learning anything new will still avoid ASP.Net MVC like the swine flu.
• The fact that the MVC pattern is a common pattern among other web development environments such as Java and PHP will also not appeal to most Microsoft developers. However the really smart ones will realize that more common knowledge will only help if you ever have to do any type of development other than microsoft development

Book Review – Pro ASP.Net MVC Framework – Steven Sanderson

Book on Amazon I am a Java, PHP, and .Net developer which may make my opinion worthless to some Microsoft zealots but I thought I would type up my thoughts on this book anyway. Overall I found this book to be a great way to learn ASP.Net MVC. It has great examples and enough background material to bring people new to the MVC pattern up to speed. Below are my pros and cons along with notes on chapters 1-13.

Note about the cover.

One thing I found interesting is that the cover says “Discover the biggest innovation in Microsoft web development since asp.net 1.0″. I find it amusing that something as old as MVC web frameworks can be called an innovation for asp.net development since MVC frameworks are nothing new to web development. Heck they are not even new to ASP.Net development. See MonoRail .

Pros

• Provides good definition of MVC and explains why you want to use it
• Overall all the examples are clear and concise
• Gives examples of how to test every part of ASP.Net MVC
• Moves quick enough for someone with MVC experience and slow enough for someone with no MVC experience
• Great chapter on web site security
• Book often demonstrates C# 3 language features

Cons

• Database examples use LINQ to SQL.
  • As many have noted this isn’t a major con. It was probably used to keep the examples shorter. Whether you like LINQ to SQL or not that is a good thing.
• No mention of Mono project or any hints of how to get ASP.Net working with Mono.
• Book examples are for the “real” version of VS2008 not the free VWDE2008.
• Does not provide a good example of using a validation utility such as XVal or Data Annotations

Chapter 1

• An adequate history lesson for those unfamiliar with MVC.

Chapter 2

• A great chapter that quickly and easily shows you the basics of ASP.Net MVC

Chapter 3

Book on Amazon

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