How to deserialise SQLAlchemy JSON to Decimal using Flask-SQLAlchemy

Question

I have got my code working to serialise an object which has Decimal and store in JSON in my PostgreSQL utilising this post here , i am using Flask-SQLAlchemy so have created my own custom apply_driver_hacks method to pass in a json_serializer which will serialise Decimal objects - so all good so far.

However on pulling the data back out , the deserializer loads these values as float. I've searched high and low but can't seem to find any way to reload as Decimal - i can pass in a custom json_deserializer as an option to Flask-SQLAlchemy but cant find a way to pass in any value such as use_decimal=True which is what I would use if using simplejson to load up Json with Decimal .

Any help greatly appreciated !

@IljaEverilä - Thank you very much! - that does indeed work and solves my problem which just a couple of lines of code, really appreciated for the insight! — W. Enzo
– W. Enzo, Commented May 25, 2018 at 10:49

Ilja Everilä · Accepted Answer · 2018-05-25 11:12:09Z

1

Pass a callable that passes parse_float=decimal.Decimal to json.loads() as json_deserializer. A simple function such as

def json_deserializer(*args, **kwgs):
    return json.loads(*args, parse_float=decimal.Decimal, **kwgs)

should do.

answered May 25, 2018 at 11:12

Ilja Everilä

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