NHibernate for the Lazies

I don't know about you, but sometimes if you want to learn a new framework, you want to see results right away. Most of the time, it never happens that way. Let's take nHibernate as an example. For somebody that is very new, you go to tutorials, how to create one and hope it works. One thing that pissed me off when I was learning NH back in the days, was writing those .hbm files.

Don't you wish there was an easy way to learn nHibernate, learn how to use sessions, transactions, unit of work, and all that good stuff? Ofcourse we have fluent-nhibernate as a good way to start up. But what if (1)you're using .net 2.0? (2)you don't like how integrated the mapping is with your application?

One day, I decided to spike a generator that generates your .hbm on the fly based on your domain objects.

Word of caution. I just used this as a spike, not a solution - More like a fast way of developing a small app without the pain of .hbm.xml files. Also, this exercise shows that you can have a domain model, totally ignorant how stuff is being saved to some kind of a persistance layer - hence mapping files. And finally it's totally doable to generate a mapping file on the fly based on your domain object.

Now let's talk code. The way this exercise was done, I was taking advantage of the Chain of responsibilty pattern to build the mapping files.

Before we go with any code, lets follow the basic rules:

1. Every .net data types are property elements
2. Every custom objects are many-to-one elements
3. Every IList<> are bag items

The Model
<br />public class Task<br />{<br /> public virtual int Id { get; set; }<br /> public virtual User User { get; set; }<br /> public virtual Priority Priority { get; set; }<br /> public virtual string Description { get; set; }<br /> public virtual string Status { get; set; }<br /> public virtual IList<comment> Comments { get; set; }<br /> public virtual DateTime CreatedDate { get; set; }<br /> public virtual DateTime? CompletedDate { get; set; }<br />}<br />

The Test
<br />[TestFixture]<br />public class HbmFilesSuckTest<br />{<br /> private readonly string expected =<br /> @"<hibernate-mapping xmlns="'urn:nhibernate-mapping-2.2'" namespace="'ezed.workstuff.domain'" assembly="'ezed.workstuff.domain'"><class name="'Task'" table="'dbo.[Task]'"><id name="'Id'" type="'Int32'"><generator class="'identity'"></id><property name="'Description'"><property name="'Status'"><property name="'CreatedDate'"><property name="'CompletedDate'"><many-to-one name="'User'" column="'UserId'" class="'ezed.workstuff.domain.User'"><many-to-one name="'Priority'" column="'PriorityId'" class="'ezed.workstuff.domain.Priority'"><bag name="'Comments'"><key column="'TaskId'"><one-to-many class="'ezed.workstuff.domain.Comment'"></bag></class></hibernate-mapping>"<br /> .Replace(@"'", @"""");<br /><br /> [Test]<br /> public void ShouldCreateValidHbmFile()<br /> {<br /> var actual = HbmFilesSuck.CreateMappingFileFrom<task>();<br /> Assert.That(actual, Is.EqualTo(expected));<br /> try<br /> {<br /> var configuration = new Configuration();<br /> configuration.Configure();<br /> configuration.AddXmlString(HbmFilesSuck.CreateMappingFileFrom<task>());<br /> configuration.AddAssembly(typeof (Task).Assembly);<br /> }<br /> catch (Exception e)<br /> {<br /> Assert.Fail(string.Format("Your hbm file is sooo wrong! {0}", e));<br /> }<br /> }<br />}<br />

The IHandler Interface
<br />public interface IHandler<br />{<br /> void HandleRequest<itemtype>(XmlDocument xml, ItemType itemType);<br />}<br />

The Mapping File Builder
<br />public class HbmFilesSuck<br />{<br /> private static readonly IHandler hibernateMappingHandler;<br /><br /> static HbmFilesSuck()<br /> {<br /> hibernateMappingHandler = new HibernateMappingHandler(<br /> new ClassNameHandler(<br /> new IdHandler(<br /> new PropertyHandler(<br /> new ManyToOneHandler(<br /> new BagHandler())))));<br /> }<br /><br /> public static string CreateMappingFileFrom<t>()<br /> {<br /> var mappingFile = new XmlDocument();<br /> hibernateMappingHandler.HandleRequest(mappingFile, Activator.CreateInstance<t>());<br /><br /> return mappingFile.OuterXml;<br /> }<br />}<br />

The Handlers
<br />public class HibernateMappingHandler : IHandler<br />{<br /> private readonly IHandler successor;<br /><br /> public HibernateMappingHandler(IHandler successor)<br /> {<br /> this.successor = successor;<br /> }<br /><br /> public void HandleRequest<itemtype>(XmlDocument xml, ItemType itemType)<br /> {<br /> var element = xml.CreateElement("hibernate-mapping")<br /> .WithAttribute("xmlns", "urn:nhibernate-mapping-2.2")<br /> .WithAttribute("namespace", itemType.GetType().Namespace)<br /> .WithAttribute("assembly", itemType.GetType().Assembly.GetName().Name);<br /> xml.AppendChild(element);<br /><br /> successor.HandleRequest(xml, itemType);<br /> }<br />}<br /><br />public class ClassNameHandler : IHandler<br />{<br /> private readonly IHandler successor;<br /><br /> public ClassNameHandler(IHandler successor)<br /> {<br /> this.successor = successor;<br /> }<br /><br /> public void HandleRequest<itemtype>(XmlDocument xml, ItemType itemType)<br /> {<br /> xml.DocumentElement.WithElement("class")<br /> .WithAttribute("name", itemType.GetType().Name)<br /> .WithAttribute("table", string.Format("dbo.[{0}]", itemType.GetType().Name));<br /> successor.HandleRequest(xml, itemType);<br /> }<br />}<br /><br />public class IdHandler : IHandler<br />{<br /> private readonly IHandler successor;<br /><br /> public IdHandler(IHandler successor)<br /> {<br /> this.successor = successor;<br /> }<br /><br /> public void HandleRequest<itemtype>(XmlDocument xml, ItemType itemType)<br /> {<br /> var idElement = xml.DocumentElement.WithElement("id").WithAttribute("name", "Id").WithAttribute("type", "Int32");<br /> idElement.WithElement("generator").WithAttribute("class", "identity");<br /><br /> xml.SelectSingleNode(@"/hibernate-mapping/class").AppendChild(idElement);<br /><br /> successor.HandleRequest(xml, itemType);<br /> }<br />}<br /><br />public class PropertyHandler : IHandler<br />{<br /> private readonly IHandler successor;<br /> public static readonly List<type> AllowedTypes;<br /><br /> static PropertyHandler()<br /> {<br /> AllowedTypes = new List<type><br /> {<br /> typeof (int),<br /> typeof (int?),<br /> typeof (bool),<br /> typeof (decimal),<br /> typeof (DateTime),<br /> typeof (DateTime?),<br /> typeof (string)<br /> };<br /> }<br /><br /> public PropertyHandler(IHandler successor)<br /> {<br /> this.successor = successor;<br /> }<br /><br /> public void HandleRequest<itemtype>(XmlDocument xml, ItemType itemType)<br /> {<br /> foreach (var property in itemType.GetType().GetProperties())<br /> {<br /> var getMethod = property.GetGetMethod();<br /> if (string.Compare(property.Name, "Id", true) == 0) continue;<br /> if (!AllowedTypes.Exists(t => t.Equals(getMethod.ReturnType))) continue;<br /><br /> var propertyElement = xml.DocumentElement.WithElement("property").WithAttribute("name", property.Name);<br /> xml.SelectSingleNode(@"/hibernate-mapping/class").AppendChild(propertyElement);<br /> }<br /> successor.HandleRequest(xml, itemType);<br /> }<br />}<br /><br />public class ManyToOneHandler : IHandler<br />{<br /> private readonly IHandler successor;<br /><br /> public ManyToOneHandler(IHandler successor)<br /> {<br /> this.successor = successor;<br /> }<br /><br /> public void HandleRequest<itemtype>(XmlDocument xml, ItemType itemType)<br /> {<br /> foreach (var property in itemType.GetType().GetProperties())<br /> {<br /> var getMethod = property.GetGetMethod();<br /> if (string.Compare(property.Name, "Id", true) == 0) continue;<br /> var returnType = getMethod.ReturnType;<br /> if (PropertyHandler.AllowedTypes.Exists(t => t.Equals(returnType))) continue;<br /> if (IsGenericCollection(returnType)) continue;<br /><br /> var propertyElement = xml.DocumentElement.WithElement("many-to-one")<br /> .WithAttribute("name", property.Name)<br /> .WithAttribute("column", string.Format("{0}Id", property.Name))<br /> .WithAttribute("class", returnType.FullName);<br /> xml.SelectSingleNode(@"/hibernate-mapping/class").AppendChild(propertyElement);<br /> }<br /> successor.HandleRequest(xml, itemType);<br /> }<br /><br /> public static bool IsGenericCollection(Type type)<br /> {<br /> return type.IsGenericType &&<br /> typeof(ICollection<>).MakeGenericType(type.GetGenericArguments()).IsAssignableFrom(type);<br /> }<br />}<br /><br />public class BagHandler : IHandler<br />{<br /><br /> public void HandleRequest<itemtype>(XmlDocument xml, ItemType itemType)<br /> {<br /> foreach (var property in itemType.GetType().GetProperties())<br /> {<br /> var returnType = property.GetGetMethod().ReturnType;<br /> if (!ManyToOneHandler.IsGenericCollection(returnType)) continue;<br /> var bagElement = xml.DocumentElement.WithElement("bag").WithAttribute("name", property.Name);<br /> bagElement.WithElement("key").WithAttribute("column", string.Format("{0}Id", itemType.GetType().Name));<br /> bagElement.WithElement("one-to-many").WithAttribute("class", returnType.GetGenericArguments()[0].FullName);<br /><br /> xml.SelectSingleNode(@"/hibernate-mapping/class").AppendChild(bagElement);<br /> }<br /><br /> }<br />}<br />


The Implementation
<br />public class SessionManager<br />{<br /> private static ISessionFactory sessionFactory;<br /><br /> private static ISessionFactory SessionFactory<br /> {<br /> get<br /> {<br /> if (sessionFactory != null) return sessionFactory;<br /><br /> var configuration = new Configuration();<br /> configuration.Configure();<br /> configuration.AddXmlString(HbmFilesSuck.CreateMappingFileFrom<task>());<br /> configuration.AddAssembly(typeof (Task).Assembly);<br /> sessionFactory = configuration.BuildSessionFactory();<br /><br /> return sessionFactory;<br /> }<br /> }<br /><br /> public static ISession OpenSession()<br /> {<br /> return SessionFactory.OpenSession();<br /> }<br />}<br />