On Sat, 2010-10-23 at 14:56 -0200, Luciano Ramalho wrote:
> I've been very intrigued by Colander, and thinking of ways I could use
> it to migrate bibliographic data from legacy ISIS databases to
> CouchDB.
>
> But here is a problem: Colander deals with missing data by generating
> nodes with a marker value, or some specified default. What we need
> when serializing bibliographic data is the option to skip the node
> altogether, and so far I have been unable to see how to specify that.
>
> For example, if an article record does not have an "institutional
> author", we don't want this serialized value:
>
> {"title": "Onthology is overrated", 'institutional_author' = colander.null}
>
> and neither this:
>
> {"title": "Onthology is overrated", 'institutional_author' = ''}
>
> This is what we need:
>
> {"title": "Onthology is overrated"}
>
> >From the documentation, I haven't seen how to make colander behave as
> described. Is there a way?
The best way to do this would be to create a subclass of
colander.Mapping which:
- omits values from the appstruct created during deserialization if
they don't exist in the input cstruct.
- omits values from the cstruct created during serialization if they
don't exist in the input appstruct.
This is mostly a matter of subclassing colander.Mapping and overriding
its "_impl" method. Let's say that subclass is called
"ForgivingMapping". Once that's done, you can do:
class ForgivingSchema(colander.Schema):
schema_type = ForgivingMapping
Then when you create schemas, you can do:
class MySchema(ForgivingSchema):
attr1 = colander.SchemaNode(...)
attr2 = colander.SchemaNode(...)
(IOW, always use ForgivingSchema to represent mappings rather than
colander.Schema).
- C
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