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Christian Simms's Software R&D, Generative Programming and other R&D.

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Evaluation of 3 Python Tools to Develop Apps with Postgresql
No, these aren't just Object Relational mapping tools. After doing applications that use O-R for several years now, I've decided that you can't completely hide the relational features from the object interface, so don't try. I looked at the following tools:

• Roundup issue tracker This is an issue tracker whose design is so good you can build an application on it. It's basically a Python app server.
  • Clever Features
    • Really simple way to specify schema. Below creates 2 tables where second table has foreign key to first:

      						 project = Class(db,"project", name=String(), creationDate=Date())
      						 task = Class(db,"task", name=String(), project=Link("project"))
      					  

      The above causes 2 main tables to be created, plus 2 shadow audit tables, plus integer primary keys. Plus it creates indexes for the foreign keys.
    • Works out of the box: just cd to its directory and run "python demo.py" and you have a fully functional bug tracking system.
    • Automatic schema upgrader -- when app server starts up, it compares current python model (as defined above) with database's schema (stored in one row of special table schema which contains a repr()'ed dictionary of information about each Class that maps to a table
    • Mail integration - has a mail filter to receive bug reports through email. This filter also archives email-based bug discussions, attaching the discussion to the appropriate bug. Wow this is a killer feature for a bug-tracking system.
  • Flaws
    • Instead of db-level triggers, it has app-level triggers -- changes made through python are stored in audit tables, but those directly through db are not.
    • Inflexible naming - for class project, it creates tables: _project and project__journal.
    • Hardcoded to use psycopg postgresql db driver (minor flaw).
• Modeling (Object-Relational Bridge for python) This is a heavy-weight modelling tool, this is what a committee would design. Reminds me of EMF (Eclipse Modelling Framework) which is just as heavyweight. If you think the way to start app development is to write a big UML model, then this is for you!
  • Clever Features
    • Has a Zope product which lets you edit your model through Zope. This sounded cool to me, but when I tried it out, it's basically a thin client data entry app -- sorry I don't need that, I like having my model defined in a text file that I can version and use in text editors.
    • Really flexible - let's you specify lots of details about each object and field, either in XML or python model. Also supports run-time APIs or generated code APIs.
  • Flaws
    • Heavyweight and complex. For instance, instead of writing SQL queries, it has its own SQL-like (but not SQL!) language.
• Twisted Enterprise ROW (R)elational (O)bject (W)rapper. A really simple way to do twisted programming against an existing db schema (yes it doesn't create the schema for you). It requires you to write a class for each table, and in this class write out how to map db columns + their types to python attributes, including PK and FK relationships.
  • Clever Features
    • Maps to whatever your existing db schema is.
  • Flaws
    • Does not create schema for you.

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