On Fri, Oct 5, 2018 at 11:02 AM Victor Reichert <vfr...@gmail.com> wrote:
>
> Hi,
>
> I have a mixin like:
>
> class BasicSqlClass(object):
>
> @declared_attr
> def __tablename__(cls):
> return convert(cls.__name__) + 's
>
>
> The mixin declares the table name and does other stuff.
>
> Hover, there is a class where I wanted to overwrite the mixed-in
> __tablename__ by declaring the __tablename__ for the class like.
>
> class SpecialClass(BasicSqlClass, db.Model):
>
> __tablename__ = 'other_table_name'
>
>
> However, that didn't work. the mixed-in __tablename__ was still used.
cannot reproduce, see MCVE below
> I also tried writing a declared attribute for the SpecialClass, but that
> didn't overwrite the mixin either.
can't reproduce that either, see below
>
> class SpecialClass(BasicSqlClass, db.Model):
>
> @declared_attr
> def __tablename__(cls):
> return 'other_table_name'
>
>
> I ended up making a special mixin to overwrite the __tablename__.
>
> class OverwriteTableName(object):
> #I needed to make a class to overwrite the table name
>
> __tablename__ = 'other_table_name'
>
>
> class SpecialClass(OverwriteTableName, BasicSqlClass, db.Model):
>
>
>
> The special mixin worked, though I was surprised I was not able to overwrite
> the mixed-in __tablename__ like a regular inherited attribute.
>
> Any thoughts on this? If the behavior is expected or intended, If perhaps a
> warning about this behavior could be added to the documentation that would be
> great. I've written a comment below, but I don't know how to propose it's
> addition to the documentation.
full MCVE, see if this script passes for you and if you can show how it fails:
from sqlalchemy import inspect, create_engine, Column, Integer
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.ext.declarative import declared_attr
Base = declarative_base()
class BasicSqlClass(object):
@declared_attr
def __tablename__(cls):
return cls.__name__ + 's'
class NormalClass(BasicSqlClass, Base):
id = Column(Integer, primary_key=True)
# mixin works
assert NormalClass.__table__.name == 'NormalClasss'
class SpecialClass(BasicSqlClass, Base):
__tablename__ = 'other_table_name'
id = Column(Integer, primary_key=True)
# regular attr overrides
assert SpecialClass.__table__.name == 'other_table_name'
class SpecialClassWDeclared(BasicSqlClass, Base):
@declared_attr
def __tablename__(cls):
return 'other_table_name_declared'
id = Column(Integer, primary_key=True)
# declared attr overrides
assert SpecialClassWDeclared.__table__.name == 'other_table_name_declared'
e = create_engine("sqlite://", echo=True)
Base.metadata.create_all(e)
# just to make sure
assert \
set(inspect(e).get_table_names()) == {
"NormalClasss", "other_table_name",
"other_table_name_declared"}
>
> <div class="admonition note">
> <p class="first admonition-title">Note</p>
> <p class="last">
> Mixed-In declared attributes can only be overridden by other mixins. A
> declared attribute inherited from a mixed-in class cannot be overridden
> directly. For example, a class has a __tablename__ attribute inherited from
> a mixin where __tablename__ is defined as a declared attribute. Just adding
> __tablename__ to the class is insufficient to overwrite the __tablename__
> inherited from the mixin for the class. A second mixin with the
> __tablename__ attribute must be declared and added to the class with
> inheritance priority over the mixin.
> </p>
> </div>
>
> I'm thinking it would go at:
>
> https://docs.sqlalchemy.org/en/latest/orm/extensions/declarative/mixins.html
> https://docs.sqlalchemy.org/en/latest/orm/extensions/declarative/api.html#sqlalchemy.ext.declarative.declared_attr
>
>
> Thanks!
>
> ~Victor
>
>
>
>
> --
> 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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