On Fri, Oct 20, 2017 at 2:40 PM, Sven <[email protected]> wrote:
> Thank you for your answer.
>
> I'm sorry, I have not been clear enough regarding the "__abstract__ = True".
>
> I suppose that I will have to add this to a lot of classes for the following
> reasons :
> 1) because it will allow me to persist the classes one by one and still be
> able to run and test the project (i will not have all the errors because
> there is no table name and no primary key). So, I would have to delete the
> "__abstract__" when I begin to work on the persistence of a new class.
> 2) because I thought that the best solution in this case is to map only the
> concrete classes. So, in my example, I would have to map "Player" and "NPC",
> but not "Character". So only the classes at the bottom of the hierarchy
> would have to be mapped. That's still a lot of classes but probably easier
> to implement.
OK, so I see you are looking to add something like "Mappable" or
similar only to those classes that are concrete.
how about this?
from sqlalchemy.ext.declarative import declarative_base, DeclarativeMeta
from sqlalchemy import Column, Integer
class MetaBase(type):
def __init__(cls, nom, bases, contenu):
type.__init__(cls, nom, bases, contenu)
print("Init MetaBase")
pass
class DeclMetaBase(MetaBase, DeclarativeMeta):
def __init__(cls, nom, bases, contenu):
super(MetaBase, cls).__init__(nom, bases, contenu)
print("Init DeclMetaBase")
Base = declarative_base(metaclass=DeclMetaBase)
class Stockable(metaclass=MetaBase):
def __init__(self):
print("Init Stockable")
class Character(Stockable, Base):
__tablename__ = 'characters'
id = Column(Integer, primary_key=True)
def __init__(self, name):
self.name = name
print("Init character")
print(repr(Character.__table__))
jean = Character("Jean")
print(jean.name)
>
> But I have to say that this is not absolutely clear for me for now. This is
> the first time I use SQLAlchemy. Do you think that this method is possible
> and is the right way to proceed ?
Whether or not it "works" involves mostly the database schema that
gets created and how reasonable this schema is from a relational /
database performance / complexity perspective. This depends a lot on
how these class hierarchies are organized and how they interact with
each other, so it's difficult to say.
>
> Le vendredi 20 octobre 2017 20:02:40 UTC+2, Mike Bayer a écrit :
>>
>>
>> CONTINUING ! sorry
>>
>>
>> On Fri, Oct 20, 2017 at 11:55 AM, Sven Dumay <[email protected]> wrote:
>>>
>>>
>>> I tried other things and I found the following solution :
>>>
>>> from sqlalchemy.ext.declarative import declarative_base, DeclarativeMeta
>>> from sqlalchemy import Column, Integer
>>>
>>> class MetaBase(DeclarativeMeta):
>>>
>>> def __init__(cls, nom, bases, contenu):
>>> super(MetaBase, cls).__init__(nom, bases, contenu)
>>> print("Init MetaBase")
>>>
>>> Base = declarative_base(metaclass = MetaBase)
>>>
>>> class Stockable(Base):
>>>
>>> __abstract__ = True
>>>
>>> def __init__(self):
>>> print("Init Stockable")
>>>
>>> class Character(Stockable):
>>>
>>> __tablename__ = 'characters'
>>> id = Column(Integer, primary_key=True)
>>>
>>> def __init__(self, name):
>>> self.name = name
>>> print("Init character")
>>>
>>>
>>> jean = Character("Jean")
>>> print(jean.name)
>>>
>>>
>>
>> this seems like roughly the correct approach.
>>
>>>
>>> It seems to work. I get the following result :
>>>
>>> >>>
>>> Init MetaBase
>>> Init MetaBase
>>> Init MetaBase
>>> Init compte
>>> Jean
>>> >>>
>>>
>>> However, the problem with this method is that I have to add "__abstract__
>>> = True" to every class which is inherited by Stockable... so, about 400
>>> classes.
>>
>>
>> I don't see why that is. If these classes are mapped to tables (which, if
>> they are persisted, they are), then there is no reason to add
>> "__abstract__". As in my previous email, how these 400 classes link
>> to tables is what needs to be answered and then we can formulate the correct
>> calling style.
>>
>>
>>>
>>> It is not very clean. Is it possible to avoid that by using something
>>> similar to my first code ? It would be great !
>>>
>>> Thank you very much.
>>>
>>> Sven
>>>
>>> --
>>> SQLAlchemy -
>>> The Python SQL Toolkit and Object Relational Mapper
>>>
>>> http://www.sqlalchemy.org/
>>>
>>> To post example code, please provide an MCVE: Minimal, Complete, and
>>> Verifiable Example. See http://stackoverflow.com/help/mcve for a full
>>> description.
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>>
>>
> --
> SQLAlchemy -
> The Python SQL Toolkit and Object Relational Mapper
>
> http://www.sqlalchemy.org/
>
> To post example code, please provide an MCVE: Minimal, Complete, and
> Verifiable Example. See http://stackoverflow.com/help/mcve for a full
> description.
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--
SQLAlchemy -
The Python SQL Toolkit and Object Relational Mapper
http://www.sqlalchemy.org/
To post example code, please provide an MCVE: Minimal, Complete, and Verifiable
Example. See http://stackoverflow.com/help/mcve for a full description.
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