-----Original Message----- >> As such writing / >> changing mapping files everytime the codebase changes is unacceptable; >> likewise marking up the code with meta-data (which another tool like xdoclet >> could use to generate a map) is also unacceptable. > > Mhh. Xdoclet is a very elegant mechanism and imposes only minimal > intrusion into the source code. I would at least think about it...
Xdoclet could be extremely elegant and impose very little BUT still be fundamentally unacceptable. The way I see it is: any such impositions are "invisible" (don't expect a compiler or any other standard tool to tell you that you're out of sync), burdensome (every programmer has to keep all the areas to sync up in mind, and any change on relevant data objects necessitates new mappings or meta-data...), and a maintenance nightmare, what if someone fails to update the mapping for a class that is sometimes (but seldom) saved off, the bug could go unnoticed (unless you have perfect testing) for a long time. Right now there's a plethora of tools (to improve on Java's serialization) but most of the ones that seem to have a good community (OJB, Castor, Hibernate) have this mapping issue. There are also a number of commercial solutions, BUT, the market seems rather fragmented and (as such) I find it dubious that the commercial solutions are really turn-key (as many claim to be). > If want to use a standardized mechanism your code must stick to some > conventions. Otherwise you need AI :-) I certainly hope it doesn't go as far as AI (but then again AI is pretty nebulous). It looks like a difficult problem but one that probably does have some reliable algorithms (rather than flaky heuristics) to solve it. The collection "mess" is one of the most difficult issues (what to do with amorphous collections like Vector). What I'm hoping for is to create an "automatic mapping" standalone, and this could be configured to make different mapping behaviors/assumptions. Given the number of solutions like OJB, Castor, and Hibernate is there some way that a hybrid community could be made (I've seen people take stabs at this auto-mapping problem before, it doesn't look like I'm the only one who is concerned with it) to implement the "other half" (an auto-mapping program, which takes an input meta-map that defines the structure and assumptions for mapping). > You can allow to Reflection to access everything. Ok, that's going to be my approach. > IMO these are all viable solutions. > But you always face some tough questions to answer: Most aren't so tough for me, but if I want to contribute to a mapping program that can help others (OJB, Castor, Hibernate,....... future tools) I need to make this flexible and configurable. > 3. how to handle collection attributes? > java collections are not typed. that is you don't know the element > type of a collection! How will you tell OJB which element-class a given > collection-descriptor will have?! That is the UGLY issue. Aside from Collections the other problems (such as arbitrary classes with inner and anon classes...) seem like they should have a solid solution (even if it is some really annoying recursion...) > 4. how to identify foreign key elements if there are multiple > associations between classes?! > Say class A holds two collections of B elements. B will then have two > foreignkey attributes. one for the first collection, one for the second. > How can you know which FK to use for which collection?! This is another possibly painful problem. > etc. etc. > Without answering these questions you are lost. IMO the only viable > solution is to have clear code-conventions that allow automated > detection of the mentioned stuff. That would be ideal, but proposing to rewrite all our code (and 3rd party code) to fit some nice convention, would never fly at this company (or most other ones). Real codebases always have some "ugliness" factor. My feeling is that things like data serialization need to be near automatic (not imposing maps or meta data), and general (not imposing a coding convention) to be truly useful. Thanks for your thoughtful input. Again, does anyone have an idea for how to build a community for working this problem out? I am thinking along the lines of something like OJB, Castor, Hibernate- an open source solution with multiple participants. A flexible mapping tool could (potentially) be plugged into all three of these code/storage solutions (as well as others). cheers, Thomas > --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
