There has been much debate over Microsoft’s first major Object Relational Mapper (ORM) called LINQ (Language-Integrated Query). Microsoft has released a several flavors of LINQ suitable for different purposes, most notably LINQ-to-SQL and LINQ-to-Entities. Most developers use LINQ-to-SQL given that LINQ-to-Entities is brand new and most info available online is about LINQ-to-SQL, so for the purposes of this article (and in most people’s minds), “LINQ” == “LINQ-to-SQL”. [Yes, I know LINQ is really an expression language and not an ORM, but let's not get technical on a technology blog. :-)]
LINQ has been met with mixed reactions from the development community. Some are enthralled that Microsoft has finally built their own “supported” ORM. Some love the ease-of-use in being able to drag tables onto a designer surface in Visual Studio 2008 (reminiscent of TableAdapters). Others like the (usually) clean and efficient SQL queries generated by the ORM.
To me, the best feature of LINQ is the integration of a strongly-typed data query language built into .NET. Gone are the days of query building from strings. Even an impressive ORM like NHibernate with its own query language (HQL) suffers from the lack of a strongly-typed query language (leading to hybrid attempts like LINQ-to-NHibernate). Altogether, it is a powerful and efficient system of data access when you understand it and use it properly.
Of course, LINQ is not without its problems and critics. I’ve heard a lot of complaints about “lack of support” for implementing dynamic queries, that is, creating queries with joins and other non-comparison criteria at runtime. There are some solutions for this like the LINQ Dynamic Query Library or Predicate Builder.
One of the biggest concerns from enterprise-level developers is that LINQ is a “black box” and the Visual Studio designer writes a ton of “hidden code” to map the entities to the database. Bear in mind that all ORMs are a black box to some degree. Even though NHibernate is open-source, most developers use a DLL from a release and never tinker with its inner workings. NHibernate extensions like Castle ActiveRecord even hide the XML column mappings from the developer. But in all honesty, LINQ-to-SQL is very bad at allowing the developer open access to the mysterious column mapping code and has a number of issues when you make changes to the underlying database schema.
A couple of months ago, I decided to try out LINQ-to-SQL on one of my pet projects. It took some getting used to, but after pulling some hair out, learning some important lessons and finding some handy tools, it worked pretty well. I even found that I can usually avoid many dynamic query issues by chaining sub-queries together to execute a single query thanks to Deferred Execution.
My biggest gripes centered around the creation and maintenance of the entity mappings in the DBML file. Microsoft’s O/R Designer documentation openly admits:
…the designer is a one-way code generator. This means that only changes that you make to the designer surface are reflected in the code file. Manual changes to the code file are not reflected in the O/R Designer. Any changes that you make manually in the code file are overwritten when the designer is saved and code is regenerated.
More than that, when you make changes to your database schema, you either need to manually update the entity through the O/R Designer or you need to delete and re-add the entity, losing any customizations you’ve made (including entity relationships). Suddenly the code-generation time savings doesn’t make up for customization frustration.
Enter “Professional LINQ to Objects,” a.k.a. PLINQO, a code generation tool for LINQ that does what you want. I’ve used other ORM frameworks from CodeSmith before, particularly NetTiers. I believe in the value of code-generation when it’s implemented properly. One of the most important attributes of a good code-gen tool is that it lets you re-generate code without overwriting your customizations. PLINQO delivers intelligent regeneration to LINQ-to-SQL.
PLINQO works by generating your DBML file for you, but surprisingly this doesn’t break Visual Studio’s O/R Designer. In fact, you can still open and modify the .dbml file with the Designer and your changes will not be overwritten next time you generate. You can also modify many aspects of the entities via code (including validation attributes) and your code customizations will be untouched by re-generation. Sweet!
Some other benefits of PLINQO (as noted on their site):
- Generates one file per entity instead of one massive [DBML] file.
- Generates partial classes where custom code can be written and won’t be overwritten.
- Generated entity files are added to the project as code behind files to their corresponding custom entity files.
- Adds customizable business rules engine to enforce entity validation, business and security rules.
- Generation of entity manager classes… Provides access to common queries based on primary keys, foreign keys, and indexes.
- Ability to automatically remove object prefix and suffixes (ie. tbl and usp) [based on RegEx].
Another nice bonus is that you configure and execute the code generation right inside VS 2008. CodeSmith Pro has Visual Studio integration that lets you add a .csp (CodeSmith Project) file inside your VS project and manage all the settings from Solution Explorer. Just right-click your .csp and select “Generate Output” and your .dbml, entities, managers and query classes appear in your solution.
If you’ve been hesitant to try LINQ because of “black box” or code re-generation concerns, now is the time to give it a shot. Download a trial of CodeSmith and try the PLINQO 2.0 release or latest development trunk. Happy coding!