Clear, if all packages are in the same project that is......
and what if in a.py I want to inherit some class mapped with b.py ....
mixin does not allways work as a solution subclassing (DeclarativeMeta) is an
option, not sure
Once I do a base=declarative_base(metadata=BaseB)
every class x(Base) gets the Columns in BaseB to it ......?
I have been setting up some tests and one way or the other I need to know how
Session is using Base, if I can have multiple declarative_base instances and
how Session relates to that.
Consider this:
Base = Declarative_base()
class a(Base):
....
....
....
def create_table(engine):
b=a()
metadata = b.metadata
metadata.create_all(engine)
Base = None # IMPORTANT IS Sessionmaker using intropsection to find out an
instance of Declarative base?
engine = ....
Session = SessionMaker(bind=engine)
would this or a similar approach work?
On Feb 8, 2011, at 9:12 PM, Michael Bayer wrote:
> the idea is like this:
>
> myproject/
> myproject/__init__.py
> myproject/meta.py
> myproject/somepackage/__init__.py
> myproject/somepackage/a.py
> myproject/someotherpackage/__init__.py
> myproject/someotherpackage/b.py
>
> myproject/__init__.py:
>
> from myproject.somepackage import a
> from myproject.someotherpackage import b
>
> meta.py:
>
> Base = declarative_base()
>
> a.py:
>
> from myproject.meta import Base
>
> b.py:
>
> from myproject.meta import Base
>
>
>
>
>
>
>
>
>
>
> On Feb 8, 2011, at 2:25 PM, Martijn Moeling wrote:
>
>> Michael,
>>
>> Do you ever sleep?
>>
>> I am not sure I get your point. How do I set up a common "Base".
>>
>> I could do Base= Declarative_base()
>>
>> from a import A (or * not sure how this differs in this case)
>> from b import B (or *)
>>
>> If I do not declare Base in module "a" I get an Import Error on class
>> A(Base), the same for importing b.
>>
>> This gets even more complicated when Base should be build from classes
>> defined across modules.
>>
>> at the end there is one main.py importing all modules and this should be
>> able to define the "Main Base".
>>
>> Any suggestions on how to tackle this. I know have multiple modules and am
>> glueing everything together. This even gets more problematic with
>> Inheritance.
>>
>> one solution could be..
>>
>> from a import A, BaseA
>> from b import B, BaseB
>>
>> Base = declarative_base()
>>
>> metadata - BaseA.metadata + BaseB.metadata
>> metadata.create_all(engine)
>>
>> What I do not get is how the mapper is configured. Normally with declarative
>> Base it is not used in "Production fase" for as far as I can see.....
>> The mapper is part of the Class right? and session does not use Base at all?
>> but gets it when needed -> Session.query(A)..... ?
>> Or am I totally wrong on this?
>>
>> Can I something like this:
>>
>> from a import * (imports class A and the declarative_base BaseA)
>>
>> Base = declarative_base()
>>
>> class C(Base):
>> .......
>>
>> BaseForB = declarative_base(metadata=BaseA)
>> class B(BaseForB)
>>
>>
>> Mixin classes are of type object so there is no issue since @declared_attr
>> etc works....
>>
>> class D(Base,mixinclass) works without a Base at all so there is no Issue....
>>
>> Am I right? in understanding your comments on my first mail in this topic?
>>
>> Martijn
>>
>>
>>
>>
>>
>>
>>
>> On Feb 8, 2011, at 7:46 PM, Michael Bayer wrote:
>>
>>>
>>> On Feb 8, 2011, at 1:19 PM, Martijn Moeling wrote:
>>>
>>>> Hi,
>>>>
>>>> I am having a small issue with multiple python modules and declarative...
>>>>
>>>> I might miss something but....
>>>>
>>>> Consider:
>>>>
>>>> a.py:
>>>>
>>>> 8<-------------------------------
>>>> Base = declarative_base()
>>>>
>>>> class A(Base):
>>>> ...
>>>> 8<-------------------------------
>>>>
>>>> b.py
>>>> Base = declarative_base()
>>>>
>>>> class B(Base):
>>>> ...
>>>> 8<-------------------------------
>>>>
>>>> c.py
>>>> Base = declarative_base()
>>>>
>>>> class C(Base):
>>>> ...
>>>> 8<-------------------------------
>>>>
>>>> d.py
>>>>
>>>> Base = declarative_base()
>>>>
>>>> from A import * # imports base....
>>>> from B import * # imports base....
>>>> from C import * # imports base....
>>>>
>>>> Class D1(Base)
>>>> ...
>>>>
>>>> Class D2(A)
>>>> ...
>>>>
>>>>
>>>> in d.py I want to create:
>>>>
>>>> def create_tables(engine):
>>>> metadata= Base.metadata
>>>> metadata.create_all(engine)
>>>>
>>>>
>>>> Is there any way to properly "add" the metadata from the imported modules
>>>> in d.py to the Base.metadata during the import......?
>>>> Think of modules a,b,c and d are together in a package and d is imported
>>>> with similar packages into something bigger....
>>>
>>> Usually the convention is that all modules in an application share the same
>>> declarative base object (i.e. Base). If you wanted multiple Base objects
>>> but have them share a common MetaData, you can declare the MetaData up
>>> front, then create each Base using declarative_base(metadata=my_metadata).
>>> Otherwise if you're really looking to merge together multiple MetaData
>>> objects, that's not really in the API right now in a clean way, you'd
>>> perhaps call .tometadata() on each Table object but that's really not what
>>> I would do here - it copies the whole Table object and isn't really for a
>>> use case like this. If you can at least have a common MetaData object, or
>>> better a common Base object, that would be the best way to go.
>>>
>>>
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>>>
>>
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>
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