Re: JSON type caster

> Uhm... but what about a new function? To be called
>
>      psycopg2.extras.register_default_json(globally=True, loads=loads)
>
> or
>      conn = psycopg2.connect(...)
>      psycopg2.extras.register_default_json(conn, loads=loads)
>

+1 for that:

it provides a simple to use interface for the use case "PG >=9.2 and
global custom json"


>> Another thing that's probably inconvenient: psycopg2.extras.Json
>> forwards kwargs for customization, but there is no trivial way
>> of using a different "json" implementation altogether
>
> What I didn't like reviewing the two sides is the asymmetry: adapter
> taking **kwargs and typecaster taking loads function. I'm thinking
> about passing a dumps function instead of the **kwargs. It could be:
>
>      class Json(object):
>          def __init__(self, adapted, dumps=None):
>              self.adapted = adapted
>              self._dumps = dumps is None and json.dumps or dumps
>
>          def dumps(self):
>              return self._dumps(self.adapted)
>
>          def getquoted(self):
>              s = self.dumps()
>              return QuotedString(s).getquoted()
>
> This way customization can be performed either functional-style via a closure:
>
>      def CustomJson(adapted):
>          return Json(adapted,
>              dumps=lambda x: simplejson.dumps(x, parse_float=Decimal))
>
> or oo-style via subclassing:
>
>      class CustomJson(Json):
>          def dumps(self)
>              return simplejson.dumps(self.adapted, parse_float=Decimal)
>

+1 for that also ..adding dump argument and dropping kwargs forwarding,
because customizing via kwargs on a per Json-instance basis is probably
the less likely case compared to "I want to use one custom loads/dumps
everywhere".

Probably the default dumps used within Json (when no specific dumps arg
was given) could even come via register_default_json i.e. when doing

psycopg2.extras.register_default_json(
globally = True,
loads = simplejson.loads,
dumps = simplejson.dumps)

which would make the symmetry accessible from 1 function.

The provided dumps would need to be stored at module level somewhere to
be accessible within Json

self._dumps = dumps is None and psycopg2.extras._dumps or dumps

Again, the argument would be that a likely use case is PG>=9.2 and
wanting to install global json loads/dumps used everywhere.

The simpler the API for that, the better. IMHO.

Wait, a problem with above: in the "per-connection variant"

psycopg2.extras.register_default_json(
conn,
loads = simplejson.loads,
dumps = simplejson.dumps)

where to store dumps so that Json instances can access it?

Mmh. There is still some asymmetry: loads is configured
globally or per connection, dumps is configured "per argument instance"
(Json instance) ..



> Thank you for the review. Comments?
>
> -- Daniele
>