Hey Matt. Class hinting was a json-rpc 1.0 feature, subsequently dropped in 1.1. But that's a nit.
The real problem, though is reconstituing those hints -- the machinery for reinstantiating those objects has to come from somewhere, and that somewhere is going to your code -- there is no magic "just add water and reconstitute" my object built into Python. If you really want to get into writing your own deserialization, you're already heading in the right direction: simplejson and cjson (and maybe others) -- have hooks to plug in your own serialization and deserialization code. I've used them both to do something almost exactly like this to serialize and deserialize JS dates, which normally can't be sent in JSON. You'll find that the built-in serialization works for *most* Python objects, especially for basic types like str(), int(), etc., but most certainly not *all* Python objects. > I don't really want to store JSON in the DB, but just use it as a > serialization format for sqlalchemy objects. We want our frontend to > render data from the same type of object with a couple different > possible backend sources. One being the database through the > sqlalchemy ORM and another being some sort of JSON/XML interface that > we can backend from whatever... Your best bet is going to be to deserialize the JSON to some intermediate object and then construct the SqlAlchemy instance. Re-implementing pickle with a JSON storage format is going to be a huge job, and really won't give you anything that you don't already get from pickle -- what other app besides you own is ever going to understand those heavily class-hinted JSON files? On 12/20/07, Matt <[EMAIL PROTECTED]> wrote: > > > On Dec 20, 5:04pm, "Rick Morrison" <[EMAIL PROTECTED]> wrote: > > You're not going to be able to serialize Python class instances in JSON: > > json strings are simple object literals limited to basic Javascript > types. > > Pickle does some pretty heavy lifting to serialize and reconstitute > class > > instances. > > I've already figured this out -- you can use class "hinting" as > outlined in this page: > > http://json-rpc.org/wiki/specification > > So a datetime using this format and converted to JSON might look like: > > "modification_time": {"__jsonclass__": ["datetime.datetime", [2007, > 12, 19, 23, 3, 2, 2]]} > > My deserialization routine loads the datetime module, then gets the > datetime attribute (which in this case is a type, but could be a > function too), and calls that with the arguments in the list. This > sort of thing works for generic classes too using the pickle > __reduce__ hooks. The JSON part I'm actually handling through cjson > or simplejson -- my serialization/deserialization is working all on > python objects. > > > Easiest way to store JSON in the database is to limit the type of data > you > > store in JSON strings to straightforward objects that only use primitive > JS > > types, and then serialize back and forth to Python dictionaries. That's > what > > libraries like SimpleJSON or cJSON do. Using Sqlalchemy, you can then > store > > those JSON strings in database VARCHARS, TEXT and so on fields. > > I don't really want to store JSON in the DB, but just use it as a > serialization format for sqlalchemy objects. We want our frontend to > render data from the same type of object with a couple different > possible backend sources. One being the database through the > sqlalchemy ORM and another being some sort of JSON/XML interface that > we can backend from whatever... > > > --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To post to this group, send email to sqlalchemy@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~----------~----~----~----~------~----~------~--~---
