[Grok-dev] Dolmen and its releases

Martin Aspeli optilude+lists at gmail.com
Thu Oct 22 11:22:10 EDT 2009

Souheil CHELFOUH wrote:
> This is one thing. The most interesting part is that we effectively
> respect the interface, providing the default, respecting the readonly,
> etc.
> For the __parent__ thing, i need to work on it more closely. I'll
> probably return a containment proxy instead.

Just a couple of suggestions from someone who's recently been working on 
very similar things (plone.namedfile, plone.app.textfield):

  - avoid proxies if you can; they cause confusion and another layer of 
  - if you need a proxy, there's the one from zope.location
  - ask yourself why it needs to know the __parent__ - avoid if you can
  - setting immutable 'value' object is better than having a mutable 
value object. You almost never need to change it, and making them 
mutable means you have to worry about persistence
  - a 'value' object probably shouldn't derive from Persistent, since it 
means you're getting a new ZODB p_jar for each one in addition to the 
parent object; you want to be in the same jar as the parent most of the 
time (or in a blob)
  - field properties that do readonly, default (mmm, you probably want 
missing_value) etc sound neat, but are less useful in practice. There's 
FieldProperties in the ZTK of course that basically do most of what you 
are doing except the __praent__ thing


Author of `Professional Plone Development`, a book for developers who
want to work with Plone. See http://martinaspeli.net/plone-book

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