Django可以很好地自动序列化从DB返回到JSON格式的ORM模型.
如何将SQLAlChemy查询结果序列化为JSON格式？
我try 了jsonpickle.encode，但它对查询对象本身进行了编码.
TypeError: <Product('3', 'some name', 'some desc')> is not JSON serializable
将SQLAlchemy ORM对象序列化为JSON/XML真的很难吗？没有默认的序列化程序吗？将ORM查询结果序列化是当今非常常见的任务.
我只需要返回SQLAlChemy查询结果的JSON或XML数据表示.
javascript数据网格(JQGrid http://www.trirand.com/blog/)中需要使用JSON/XML格式的SQLAlchemy对象查询结果
你可以用这样的方法:
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(将其设置为"无").
它不会自动扩展关系(因为这可能会导致自引用，并永远循环).
但是，如果您希望永远循环，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
然后使用以下命令对对象进行编码:
print json.dumps(e, cls=new_alchemy_encoder(), check_circular=False)
这将对所有的子元素，他们的子元素，他们的子元素进行编码...基本上，可以对整个数据库进行编码.当它到达之前编码的东西时，它会将其编码为"无".
另一种可能更好的替代方法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
现在，您可以通过以下方式进行调用:
print json.dumps(e, cls=new_alchemy_encoder(False, ['parents']), check_circular=False)
例如，仅扩展名为"parents"的SQLAlchemy字段.