一个具有不同数据类型的字段[SQLAlchemy] [英] one field with different data types [SQLAlchemy]
问题描述
#declarative
class MyClass(Base)
#id和其他列
_value_str =列(String(100))
_value_int =列(整数)
_value_float =列(Float)
def __init __(self,...,value):
self._value_str = value if isinstance(value,(str,unicode))else None
self._value_int = value if isinstance(value,int)else None
self._value_float = value if isinstance(value,float)else None
,我想做这样的事情:
>> ; value ='text'
>>> my_class = MyClass(value,...)
>>> my_class.value
>>> 'text'
>>> session.add(my_class)
>>> session.commit()
#specialy this
>>> result = session.query(Myclass).filter(Myclass.value =='text')。one()
>>> print result.value
>>> 'text'
也许我有一个设计问题,我接受任何好主意
我是SQLAlchemy中的新朋友
谢谢
可能是一个设计问题 - 你的数据库和Python之间的一个不匹配。在SQL变量(列)中有一个类型,而在python值中有类型。
一种可能是使用单个列(字符串)存储之前的价值。
这可以通过 sqlalchemy自定义类型。
沿着以下行的某些东西(使用 jsonpickle 进行转换而不是cpickle):
import sqlalchemy.types as types
import jsonpickle
from copy import deepcopy
class JsonType(types.MutableType,types.TypeDecorator):
impl = types.Unicode
def process_bind_param(self,value,engine):
return unicode(jsonpickle.encode(value))
def process_result_value ,value,engine):
如果值:
rv = jsonpickle.decode(value)
return rv
else:
return无
def copy_value(self,value):
return deepcopy(value)
def compare_values(self,x,y):
return x == y
然后使用它如下:
code> class MyClass(base):
value =列(JsonType())
I have a value that can be integer, float or string, and I created different columns:
#declarative
class MyClass(Base):
#id and other Columns
_value_str = Column(String(100))
_value_int = Column(Integer)
_value_float = Column(Float)
def __init__(self,...,value):
self._value_str = value if isinstance(value,(str,unicode)) else None
self._value_int = value if isinstance(value,int) else None
self._value_float = value if isinstance(value,float) else None
and i would like to do something like this:
>>> value = 'text'
>>> my_class = MyClass(value, ...)
>>> my_class.value
>>> 'text'
>>> session.add(my_class)
>>> session.commit()
#specialy this
>>> result = session.query(Myclass).filter(Myclass.value == 'text').one()
>>> print result.value
>>> 'text'
Maybe i have a design problem, i accept any good idea
I'm newbe in SQLAlchemy
Thanks
Probably a design problem - a bit of a mismatch between your DB and Python. In SQL variables (columns) have a type, whereas in python values have the type.
One possibility would be to use a single column (a string), but pickle the value before you store it.
This can be accomplished automatically with a sqlalchemy custom type.
Something along the lines of the following (uses jsonpickle to do the conversion rather than cpickle):
import sqlalchemy.types as types
import jsonpickle
from copy import deepcopy
class JsonType(types.MutableType, types.TypeDecorator):
impl = types.Unicode
def process_bind_param(self, value, engine):
return unicode(jsonpickle.encode(value))
def process_result_value(self, value, engine):
if value:
rv = jsonpickle.decode(value)
return rv
else:
return None
def copy_value(self, value):
return deepcopy(value)
def compare_values(self, x, y):
return x == y
And then use it as follows:
class MyClass(base):
value = Column(JsonType())
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