NHibernate 2 Beginner's Guide Review

Wednesday, June 9, 2010

NHibernate 2 Beginner's Guide

OK, here's the review I promised a while ago.

This is a beginner's introduction to NHibernate, so if you have already some experience with NHibernate, you will notice it lacks a lot of concepts and information.

It starts with a good description of NHibernate and why would we use it. It goes on describing basic mapping scenarios having primary keys generated with the HiLo or Identity algorithms, without actually explaining why would we choose one over the other.

As for mapping, the book talks about XML mappings and provides a simple example of Fluent NHibernate, comparing it to its XML counterpart.

When it comes to relations, it covers one-to-many/many-to-one and many-to-many, not one-to-one relations, but only talks briefly about lazy loading, which is, IMO, an important concept. Only Bags are described, not any of the other collection types.

The log4net configuration description gets it's own chapter, which I find excessive.

The chapter on configuration merely lists the most common properties for configuring NHibernate, both in XML and in code.

Querying only talks about loading by ID (using Get, not Load) and using Criteria API, on which a paging example is presented as well as some common filtering options (property equals/like/between to, no examples on conjunction/disjunction, however).

There's a chapter fully dedicated to ASP.NET, which explains how we can use NHibernate in web applications. It basically talks about ASP.NET concepts, though. Following it, another chapter explains how we can build our own ASP.NET providers using NHibernate (Membership, Role).

The available entity generators for NHibernate are referred and evaluated on a chapter of their own, the list is fine (CodeSmith, nhib-gen, AjGenesis, Visual NHibernate, MyGeneration, NGen, NHModeler, Microsoft T4 (?) and hbm2net), examples are provided whenever possible, however, I have some problems with some of the evaluations: for example, Visual NHibernate scores 5 out of 5 on Visual Studio integration, which simply does not exist! I suspect the author means to say that it can be launched from inside Visual Studio, but then, what can't?

Finally, there's a chapter I really don't understand. It seems like a bag where a lot of things are thrown in, like NHibernate Burrow (which actually isn't explained at all), Blog.Net components, CSS template conversion and web.config settings related to the maximum request length for file uploads and ending with XML comments, with the help of GhostDoc.

Like I said, the book is only good for absolute beginners, it does a fair job in explaining the very basics, but lack a lot of not-so-basic concepts. Among other things, it lacks:

Inheritance mapping strategies (table per class hierarchy, table per class, table per concrete class)
Load versus Get usage
Other usefull ISession methods
First level cache (Identity Map pattern)
Other collection types other that Bag (Set, List, Map, IdBag, etc
Fetch options
User Types
Filters
Named queries
LINQ examples
HQL examples