On Fri, Oct 20, 2017 at 3:15 PM, Mike Bayer <[email protected]> wrote:
> 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")
actually like this:
class DeclMetaBase(MetaBase, DeclarativeMeta):
def __init__(cls, nom, bases, contenu):
MetaBase.__init__(cls, nom, bases, contenu)
DeclarativeMeta.__init__(cls, 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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>>>> For more options, visit https://groups.google.com/d/optout.
>>>
>>>
>> --
>> 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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