是否有一种简单的方法来遍历列名和值对?
我的SQLAlchemy版本是0.5.6
下面是我尝试使用dict(row)的示例代码:
import sqlalchemy
from sqlalchemy import *
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker
print "sqlalchemy version:",sqlalchemy.__version__
engine = create_engine('sqlite:///:memory:', echo=False)
metadata = MetaData()
users_table = Table('users', metadata,
Column('id', Integer, primary_key=True),
Column('name', String),
)
metadata.create_all(engine)
class User(declarative_base()):
__tablename__ = 'users'
id = Column(Integer, primary_key=True)
name = Column(String)
def __init__(self, name):
self.name = name
Session = sessionmaker(bind=engine)
session = Session()
user1 = User("anurag")
session.add(user1)
session.commit()
# uncommenting next line throws exception 'TypeError: 'User' object is not iterable'
#print dict(user1)
# this one also throws 'TypeError: 'User' object is not iterable'
for u in session.query(User).all():
print dict(u)
在我的系统输出上运行这段代码:
Traceback (most recent call last):
File "untitled-1.py", line 37, in <module>
print dict(u)
TypeError: 'User' object is not iterable
我对使用(太多?)字典的看法:
def serialize(_query):
#d = dictionary written to per row
#D = dictionary d is written to each time, then reset
#Master = dictionary of dictionaries; the id Key (int, unique from database) from D is used as the Key for the dictionary D entry in Master
Master = {}
D = {}
x = 0
for u in _query:
d = u.__dict__
D = {}
for n in d.keys():
if n != '_sa_instance_state':
D[n] = d[n]
x = d['id']
Master[x] = D
return Master
使用flask(包括jsonify)和flask_sqlalchemy将输出打印为JSON。
使用jsonify(serialize())调用该函数。
与我迄今为止尝试过的所有SQLAlchemy查询一起工作(运行SQLite3)
如OP所述，调用dict初始化器会引发一个异常，消息为“User”对象不可迭代。所以真正的问题是如何使一个SQLAlchemy模型可迭代?
We'll have to implement the special methods __iter__ and __next__, but if we inherit directly from the declarative_base model, we would still run into the undesirable "_sa_instance_state" key. What's worse, is we would have to loop through __dict__.keys() for every call to __next__ because the keys() method returns a View -- an iterable that is not indexed. This would increase the time complexity by a factor of N, where N is the number of keys in __dict__. Generating the dict would cost O(N^2). We can do better.
我们可以实现自己的基类，它实现所需的特殊方法，并存储可以通过索引访问的列名列表，从而降低生成O(N)字典的时间复杂性。这有一个额外的好处，我们可以定义一次逻辑，并在任何时候从基类继承，我们希望我们的模型类是可迭代的。
class IterableBase(declarative_base()):
__abstract__ = True
def _init_keys(self):
self._keys = [c.name for c in self.__table__.columns]
self._dict = {c.name: getattr(self, c.name) for c in self.__table__.columns}
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
self._init_keys()
def __setattr__(self, name, value):
super().__setattr__(name, value)
if name not in ('_dict', '_keys', '_n') and '_dict' in self.__dict__:
self._dict[name] = value
def __iter__(self):
self._n = 0
return self
def __next__(self):
if self._n >= len(self._keys):
raise StopIteration
self._n += 1
key = self._keys[self._n-1]
return (key, self._dict[key])
现在User类可以直接从IterableBase类继承。
class User(IterableBase):
__tablename__ = 'users'
id = Column(Integer, primary_key=True)
name = Column(String)
您可以确认，以User实例作为参数调用dict函数将返回所需的字典，没有"_sa_instance_state"。你可能已经注意到在IterableBase类中声明的__setattr__方法。这确保在初始化后属性发生变化或设置时更新_dict。
def main():
user1 = User('Bob')
print(dict(user1))
# outputs {'id': None, 'name': 'Bob'}
user1.id = 42
print(dict(user1))
# outputs {'id': 42, 'name': 'Bob'}
if __name__ == '__main__':
main()
我是一个新晋的Python程序员，遇到了使用join表获取JSON的问题。使用这里的答案中的信息，我构建了一个函数，将合理的结果返回到JSON，其中包括表名，避免使用别名或字段冲突。
简单地传递会话查询的结果:
test = Session()。查询(VMInfo、客户). join(客户).order_by (VMInfo.vm_name) .limit (50) .offset (10)
json = sqlAl2json（test）
def sqlAl2json(self, result):
arr = []
for rs in result.all():
proc = []
try:
iterator = iter(rs)
except TypeError:
proc.append(rs)
else:
for t in rs:
proc.append(t)
dict = {}
for p in proc:
tname = type(p).__name__
for d in dir(p):
if d.startswith('_') | d.startswith('metadata'):
pass
else:
key = '%s_%s' %(tname, d)
dict[key] = getattr(p, d)
arr.append(dict)
return json.dumps(arr)
