A Look At .NET ORMs - Part 2

September 09, 2010

Persistor.NET Express

www.persistor.net

Persistor is a commercial ORM but features a community edition like many commercial software tools do now. I tried it out but didn’t bother writing any CRUD code with it, or querying as its free version was really too restrictive to be any use to anyone except the complete ASP.NET beginner doing their first website.

The Pros

Works with zero configuration with SQL Express, defines and creates the schema for you
As with db4o, this makes automated testing a lot easier
Good documentation
As it’s commercial it has regular updates

The Cons

(Free edition) SQL Server Express only
Uses a very strange way of storing objects - doesn’t just map tables to classes and columns to properties, but seems to use SQL in a non-relational way.
Doesn’t use joins for its schema - relationships are added as columns on the table, e.g. Employee.Person.Name would be stored as a column called Employee.Person.Name.
Doesn’t work with existing databases
Doesn’t support nullable types
(Free edition) no lazy loading or retrieving objects by id.
Not as flexible as other ORMs
Forum is a ghost town
Seems to store POCOs (plain old CLR objects) definitions in the database too.

Example

	[Serializable]
	public class Person
	{
	public Guid Id { get; set; }
	public string Name { get; set; }
	public string Email { get; set; }
	}

	public class PersonManager
	{
	public static void Example()
	{
	// Doesn't require app.config/web.config settings
	Persistor persistor = new Persistor();

	// Save example
	Person person = new Person();
	person.Id = Guid.NewGuid();
	person.Name = "John";
	person.Email = "john@aol.com";
	persistor.Save(person);

	// A simple load
	IList<Person> list = persistor.Retrieve<Person>();

	// Filtered loading
	list = persistor.Retrieve<Person>( delegate(Person p){ return p.Name == "John" } );
	}
	}

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Paladin

www.codeplex.com/paladin

I’ve used Paladin previously for some mid-sized projects. It works in the way the Entity Framework works, by having a generator create your entity classes for you, it differs though as it uses the Active Record pattern approach, where you save on the domain objects themselves, e.g Person person = new Person(); person.Save();

The codeplex project doesn’t link to the forums but they can be found here: community.sgdotnet.org/forums/50.aspx and the documentation at community.sgdotnet.org/forums/t/3332.aspx.

The framework was available from this site before it reached codeplex in 2007. It seems to be a dead project now so it wouldn’t be advisable for anything except to play around with, and pros and cons seem a bit useless as it doesn’t compete with the other ORMs really, I just thought I’d give it a mention.

NPersist

www.codeplex.com/PuzzleNPersist
www.puzzleframework.com

NPersist is one of the contenders for NHibernate/ActiveRecord in my view, and has a lot of features that sell an ORM to me. The main of these is querying via linq, comprehensive documentation and being able to specify relationships in attributes or XML. Unfortunately the forum seems to be a bit dead since February 2008 and all the examples are locked inside a doc file instead of on the website. This can make finding details via search engines difficult.

All operations in NPersist work via a session, or context (facade class). Unlike the Entity framework though, this doesn’t appear to lose its scope but does mean you end up passing the context around outside the “business layer” if you need to perform tasks in other worker classes (for example, if you had namespace that performed all crawling of websites in a search engine).

The Pros

Supports XML entity definition files, and also attributes
Thorough documentation - 200 page manual
Impressive feature list
Has its own query language NPath, just like SQL and also linq.
Includes validation
All new objects are created via a factory class, making object identity confusion less messy.

The Cons

Only 3 contributors (though this isn’t really a small amount)
Last updated in February and quiet forums
No web-based help, it’s all inside a large Word document.
All new objects are created via a factory, making “offline” creation hard, or meaning the context has to be passed around.
As with the Entity Framework, NPersist’s context model means all the object belong to the context they were created in, although it’s not as restrictive (i.e. doesn’t have the one context only bug) as the EF one.

Example

	[ClassMap(Table = "People")]
	public class Person
	{
	[PropertyMap(Columns = "EmployeeId", IsIdentity = true, IsAssignedBySource = true)]
	public virtual Guid Id { get; set; }
	[PropertyMap(Columns = "Name")]
	public virtual string Name { get; set; }
	[PropertyMap(Columns = "Email")]
	public virtual string Email { get; set; }
	}

	// These are required in your assemblyinfo
	[assembly: DomainMap(Source = "HelloWorldSource")]
	[assembly: SourceMap(Compute = true, Name = "HelloWorldSource")]

	public class PersonManager
	{
	public static void Example()
	{
	using (IContext context = GetContext())
	{
	// app.config/web.config settings would be used in GetContext()
	Person person = (Person)context.CreateObject(typeof(Person));
	person.Id = Guid.NewGuid(); // This might not be needed
	person.Name = "John";
	person.Email = "john@aol.com";
	context.Commit();
	Person person = (Person)context.GetObjectById(Guid.NewGuid()); // this would be a proper guid
	IList<Person> list = context.GetObjects(typeof(Employee));

	// Filtered loading, basically SQL
	NPathQuery query = new NPathQuery("Select * from Person Where Name=?", typeof(Person));
	query.Parameters.Add(new QueryParameter(DbType.AnsiString, "John"));
	list = context.GetObjectsByNPath(query);
	}
	}

	private IContext GetContext()
	{
	IContext context = new Context(this.GetType().Assembly);
	context.SetConnectionString("server=(local);uid=xxx;pwd=xxx;database=yourdb;");
	return context;
	}
	}

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Subsonic

www.codeplex.com/subsonic

Update:
Version 3 is now available, and is a complete rewrite. It has some nice new features including T3 templates, LINQ support and a SimpleRepository that allows you to persist basic classes (no relationships are supported) with the need for attribute decoration.

The information and code below is based on Subsonic 2.

Subsonic is a kind of amalgamation of the Entity framework and ActiveRecord with no custom querying language. The whole package is very slick and friendly to use. I was put off by the generator and reams of code that it produced, even though it was very quick to get going. It has the clever facility for working with the web 2.0 style web apps (appdata folder style) via its own build provider, though this style of project isn’t something I use and have never liked the appdata etc. model.

The Pros

Uses the Active Record pattern
9 Contributors
Good documentation howtos and active forums
Last update August 2009
Well marketed so there’s plenty of guides for getting started and performing tasks
Bundled with a useful winforms app for editing data with.
Intuitive and fast to use
Querying is performed using method names for SQL actions - .InnerJoin() and so on.

The Cons

Relies on the generator to produce your entity classes, doing it manually is like the Entity framework - lots of work is involved.
“Subsonic <3”, “All your database belong to us” - The Conservative world of enterprise middle tier just isn’t ready for the netspeak!
I had problems with the SQL parser (Ansi92 generator), it suffered from null reference exceptions doing a 3 table joins. But being open source atleast I could find the bug

Example

	// This class is autogenerated for you by SubSonic, so it's a lot larger than this.
	public class Person
	{
	public Guid Id { get; set; }
	public string Name { get; set; }
	public string Email { get; set; }
	}

	public class PersonManager
	{
	public static void Example()
	{
	// Requires app.config/web.config settings (a SubSonicService node)
	int page = 1;
	int itemsPerPage = 10;

	// Save example
	Person person = new Person();
	person.Id = Guid.NewGuid();
	person.Name = "John";
	person.Email = "john@aol.com";
	person.Save();

	// Number of records
	int count = new Select().From(Person.Schema).GetRecordCount();

	// All items
	IList<Person> list = Select().From(Person.Schema).OrderAsc("Name").ExecuteTypedList<Person>();

	// Paging
	SubSonic.SqlQuery q = new Select().From(Person.Schema).InnerJoin(Address.Schema);

	// You can append predicates like below
	q = q.Where(Address.StreetColumn).IsEqualTo("Long Road");
	list = q.Paged(page, itemsPerPage).ExecuteTypedList<FeedItem>();
	}
	}

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Part 3 >>

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I'm Chris Small, a software engineer working in London. This is my tech blog. Find out more about me via Github, Stackoverflow, Resume