from sqlalchemy.ext.declarative import DeclarativeMeta
from flask import json

class AlchemyEncoder(json.JSONEncoder):
  def default(self, o):
    if isinstance(o.__class__, DeclarativeMeta):
      data = {}
      fields = o.__json__() if hasattr(o, '__json__') else dir(o)
      for field in [f for f in fields if not f.startswith('_') and f not in ['metadata', 'query', 'query_class']]:
        value = o.__getattribute__(field)
        try:
          json.dumps(value)
          data[field] = value
        except TypeError:
          data[field] = None
      return data
    return json.JSONEncoder.default(self, o)