平面实施
你可以使用如下形式：

from sqlalchemy.ext.declarative import DeclarativeMeta

class AlchemyEncoder(json.JSONEncoder):

    def default(self, obj):
        if isinstance(obj.__class__, DeclarativeMeta):
            # an SQLAlchemy class
            fields = {}
            for field in [x for x in dir(obj) if not x.startswith('_') and x != 'metadata']:
                data = obj.__getattribute__(field)
                try:
                    json.dumps(data) # this will fail on non-encodable values, like other classes
                    fields[field] = data
                except TypeError:
                    fields[field] = None
            # a json-encodable dict
            return fields

        return json.JSONEncoder.default(self, obj)

然后使用以下命令转换为JSON：

c = YourAlchemyClass()
print json.dumps(c, cls=AlchemyEncoder)

它将忽略不可编码的字段（将它们设置为“无”）。

它不会自动展开关系（因为这可能导致自我引用，并永远循环）。

递归的非循环实现
但是，如果你希望永久循环，则可以使用：

from sqlalchemy.ext.declarative import DeclarativeMeta

def new_alchemy_encoder():
    _visited_objs = []

    class AlchemyEncoder(json.JSONEncoder):
        def default(self, obj):
            if isinstance(obj.__class__, DeclarativeMeta):
                # don't re-visit self
                if obj in _visited_objs:
                    return None
                _visited_objs.append(obj)

                # an SQLAlchemy class
                fields = {}
                for field in [x for x in dir(obj) if not x.startswith('_') and x != 'metadata']:
                    fields[field] = obj.__getattribute__(field)
                # a json-encodable dict
                return fields

            return json.JSONEncoder.default(self, obj)

    return AlchemyEncoder

然后使用以下代码编码对象：

print json.dumps(e, cls=new_alchemy_encoder(), check_circular=False)

这将对所有子项，所有子项以及所有子项进行编码。基本上，可能对整个数据库进行编码。当它到达之前已编码的内容时，会将其编码为“无”。

递归（可能是循环的）选择性实现
另一种可能更好的选择是能够指定要扩展的字段：

def new_alchemy_encoder(revisit_self = False, fields_to_expand = []):
    _visited_objs = []

    class AlchemyEncoder(json.JSONEncoder):
        def default(self, obj):
            if isinstance(obj.__class__, DeclarativeMeta):
                # don't re-visit self
                if revisit_self:
                    if obj in _visited_objs:
                        return None
                    _visited_objs.append(obj)

                # go through each field in this SQLalchemy class
                fields = {}
                for field in [x for x in dir(obj) if not x.startswith('_') and x != 'metadata']:
                    val = obj.__getattribute__(field)

                    # is this field another SQLalchemy object, or a list of SQLalchemy objects?
                    if isinstance(val.__class__, DeclarativeMeta) or (isinstance(val, list) and len(val) > 0 and isinstance(val[0].__class__, DeclarativeMeta)):
                        # unless we're expanding this field, stop here
                        if field not in fields_to_expand:
                            # not expanding this field: set it to None and continue
                            fields[field] = None
                            continue

                    fields[field] = val
                # a json-encodable dict
                return fields

            return json.JSONEncoder.default(self, obj)

    return AlchemyEncoder

你现在可以通过以下方式调用它：

print json.dumps(e, cls=new_alchemy_encoder(False, ['parents']), check_circular=False)

例如，仅扩展名为“父母”的SQLAlchemy字段。