Another View of Code Generation

Karl on WPF posted this on code generators.


Karl appears to be largely talking about issues within existing MS code generation tools. The underlying problem, is that Microsoft does not have a code generation group that understands code generation from an application perspective and acts as a core resource to demand standard metadata, force Visual Studio support, explore problems like the attribute issue Karl raises and a host of other issues. There’s certainly a team around the CodeDOM, but it is entirely inappropriate for our use. And there’s one around DSL, but it’s not language neutral and it’s not incorporated by teams.

For the seven years I’ve been doing code generation and talking about it outside Microsoft I have never found a single person inside Microsoft that understands code generation the way Karl, Steele, Miguel, and the dozens of other people that actually fight through using code generation understand it. While I think I’ve had a few important ideas, the overwhelming majority of what I’ve thought and written is the same thing almost anyone who spent as much time as I have with code generating real applications would come to. This is NOT magic; it’s NOT core research anymore. It’s a well known discipline with well known problems and it’s about jolly time Microsoft stopped playing at the edges and got serious about it.

Metadata is my second core principal and the lack of standard metadata that Karl talks about is a real problem. If I a genie gave me three wishes, I would stop world hunger, turn half the teachers in elementary schools into men, and poof! create a rich robust standard metadata structure. OK, maybe I’d pick my priorities a little different if the genie actually shows up.

We sort of have standard metadata now. The problem is its too wimpy and it was designed without an extensibility model. The standard metadata is the Entity Framework edmx, and it’s a huge step. The problem is the combination of wimpiness and lack of extensibility model. As soon as we add something simple like plurals, you and I do it differently and the metadata is no longer standard.

You and I will have some extreme side cases, but 99% of our metadata will be the same content and must use the same approach. For example, Karl wants to put the “pull-down” data in the table (the high school graduated from in the college student table). I think he’s wrong. Foreign keys are always combo boxes or another lookup style and the primary key table (the high school table) should be responsible for telling the outside world what it needs to display:

· I’m a static lookup – you can cache me

· The short name for each row is in this field

· The long name for each row is in these fields concatenated like this

· I have about x records so you know what style of UI makes sense to you

· I can be filtered on these fields (optional- country/region problem)

This illustrates that metadata always looks simpler at first blush than when you spend years with it. But there are a dozen people in this country that could come together and crate a metadata standard that we could live with for a very long time. And it wouldn’t look like the gobbledygook that OMG created. Simple clear rich metadata as the bar we all reach and metadata would never be the same. Tools would quickly arise to fill that structure – including UI tools and storage models for the parts of it you can’t extract from databases. The only way this can happen is for Microsoft to get serious about the problem, call a summit, then be willing for the result to differ markedly from anything they currently have leaving a lot of work for all of us to do.

As a side effect, this would open the door for model driven (as opposed to database driven) design.We’re using databases as our prime source because a) we know how to make them and b) it’s the only structure we can guarantee will have meaning in five or ten years. No metadata structure today has that guarantee. Standard metadata would remove that major hurdle in improving the overall we create applications. Code generation is one little cog – but since its broken the whole machine doesn’t work. Fixing it will expose the next cog that’s broken, but there is a sane way to develop applications and writing 2 million lines, or even 10,000 lines of semi-static code is not it.

In the meantime, look for the GenDotNet generator to isolate metadata in a separate pluggable layer to allow use with a variety of metadata formats. This insulates you from many types of metadata changes. It’s the best we can do today.

Hopefully I’ve finally found a puppy and I am desperately trying to tie up loose ends to drive to Ogallala Nebraska so I’m putting this post up without my usual edits. Please let me know if I garbled any of it.

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