Re: [sqlalchemy] override relationship in subclass
On Feb 11, 2014, at 9:38 PM, Eric Atkin eat...@certusllc.us wrote:
Hi,
I want to override a relationship in a subclass to relate to a subclass of
the base attributes' related class. Perhaps an example of how I thought it
should work:
{{{
class Load(Base):
__tablename__ = 'load'
__mapper_args__ = {
'polymorphic_identity':'load',
'polymorphic_on':'polymorphic_type',
}
id = Column(Integer, primary_key=True)
polymorphic_type = Column(Text, nullable=False)
source_id = Column(Integer, ForeignKey('source.id'))
source = relationship('Source')
class Production_Load(Load):
__tablename__ = 'production_load'
__mapper_args__ = { 'polymorphic_identity':'production_load' }
id = Column(Integer, ForeignKey('load.id'), primary_key=True)
source_id = Column(Integer, ForeignKey('measured_source.id'))
source = relationship('Measured_Source')
class Source(Base):
__tablename__ = 'source'
__mapper_args__ = {
'polymorphic_identity':'source',
'polymorphic_on':'polymorphic_type',
}
id = Column(Integer, primary_key=True)
polymorphic_type = Column(Text, nullable=False)
class Measured_Source(Source):
__tablename__ = 'measured_source'
__mapper_args__ = { 'polymorphic_identity':'measured_source' }
id = Column(Integer, ForeignKey('source.id'), primary_key=True)
}}}
As you can see, we have Load.source - Source and I want
Production_Load.source - Measured_Source, but when I import the models, I
get the following warning:
{...}/env/lib/python2.7/site-packages/sqlalchemy/orm/properties.py:1028:
SAWarning: Warning: relationship 'source' on mapper
'Mapper|Production_Load|production_load' supersedes the same relationship on
inherited mapper 'Mapper|Load|load'; this can cause dependency issues during
flush
and when I try to use Production_Load.source (class level attr) in a query, I
get the following error:
AttributeError: Neither 'InstrumentedAttribute' object nor 'Comparator'
object associated with Production_Load.source has an attribute 'conversion'
Is such a thing possible, even with a re-factor of the models?
“conversion” sounds like an attribute name on your end, but generally being
able to supersede a relationship like that when the inheritance is not
“concrete” is not supported. you’d need to name it to something else.
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Re: [sqlalchemy] override relationship in subclass
Couldn't it be handled with a mixin?
{{{
class _LoadCore(Base):
whatever you want for both classes here
pass
class Load(_LoadCore):
__tablename__ = 'load'
__mapper_args__ = {
'polymorphic_identity':'load',
'polymorphic_on':'polymorphic_type',
}
id = Column(Integer, primary_key=True)
polymorphic_type = Column(Text, nullable=False)
source_id = Column(Integer, ForeignKey('source.id'))
source = relationship('Source')
class Production_Load(_LoadCore):
__tablename__ = 'production_load'
__mapper_args__ = { 'polymorphic_identity':'production_load' }
id = Column(Integer, ForeignKey('load.id'), primary_key=True)
source_id = Column(Integer, ForeignKey('measured_source.id'))
source = relationship('Measured_Source')
}}
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Re: [sqlalchemy] override relationship in subclass
Yeah sorry I missed that. conversion is an attribute on Measured_Source.
So the intent is that a Production_Load is a Load with its own additional
attributes over Load as well as a constraint that its source is a
Measured_Source which has its own attribute extensions over Source. One of
the goals here is to add that constraint enforcement. I was able to make it
work with the following hybrid_method and hybrid_method.expression, but the
isinstance(Production_Load.source, Measured_Source) enforcement is missing.
Eric
{{{
class Production_Load(Load):
__tablename__ = 'production_load'
__mapper_args__ = { 'polymorphic_identity':'production_load' }
id = Column(Integer, ForeignKey('load.id'), primary_key=True)
top = Column(Numeric, nullable=False)
bottom = Column(Numeric, nullable=False)
@hybrid_method
def delta(self):
return (self.top-self.bottom)*self.source.conversion if self.source
else None
@gdelta.expression
def delta(self):
# not sure about the performance here
return
(self.top-self.bottom)*select([Measured_Source.conversion]).where(Measured_Source.id==self.source_id).label('delta')
}}}
On Wednesday, February 12, 2014 7:17:08 AM UTC-7, Michael Bayer wrote:
On Feb 11, 2014, at 9:38 PM, Eric Atkin eat...@certusllc.us javascript:
wrote:
Hi,
I want to override a relationship in a subclass to relate to a subclass
of the base attributes' related class. Perhaps an example of how I thought
it should work:
{{{
class Load(Base):
__tablename__ = 'load'
__mapper_args__ = {
'polymorphic_identity':'load',
'polymorphic_on':'polymorphic_type',
}
id = Column(Integer, primary_key=True)
polymorphic_type = Column(Text, nullable=False)
source_id = Column(Integer, ForeignKey('source.id'))
source = relationship('Source')
class Production_Load(Load):
__tablename__ = 'production_load'
__mapper_args__ = { 'polymorphic_identity':'production_load' }
id = Column(Integer, ForeignKey('load.id'), primary_key=True)
source_id = Column(Integer, ForeignKey('measured_source.id'))
source = relationship('Measured_Source')
class Source(Base):
__tablename__ = 'source'
__mapper_args__ = {
'polymorphic_identity':'source',
'polymorphic_on':'polymorphic_type',
}
id = Column(Integer, primary_key=True)
polymorphic_type = Column(Text, nullable=False)
class Measured_Source(Source):
__tablename__ = 'measured_source'
__mapper_args__ = { 'polymorphic_identity':'measured_source' }
id = Column(Integer, ForeignKey('source.id'), primary_key=True)
}}}
As you can see, we have Load.source - Source and I want
Production_Load.source - Measured_Source, but when I import the models, I
get the following warning:
{...}/env/lib/python2.7/site-packages/sqlalchemy/orm/properties.py:1028:
SAWarning: Warning: relationship 'source' on mapper
'Mapper|Production_Load|production_load' supersedes the same relationship
on inherited mapper 'Mapper|Load|load'; this can cause dependency issues
during flush
and when I try to use Production_Load.source (class level attr) in a
query, I get the following error:
AttributeError: Neither 'InstrumentedAttribute' object nor 'Comparator'
object associated with Production_Load.source has an attribute 'conversion'
Is such a thing possible, even with a re-factor of the models?
“conversion” sounds like an attribute name on your end, but generally
being able to supersede a relationship like that when the inheritance is
not “concrete” is not supported. you’d need to name it to something else.
--
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Re: [sqlalchemy] override relationship in subclass
@gdelta.expression is a typo. Should be @delta.expression.
On Wednesday, February 12, 2014 11:53:05 AM UTC-7, Eric Atkin wrote:
Yeah sorry I missed that. conversion is an attribute on Measured_Source.
So the intent is that a Production_Load is a Load with its own additional
attributes over Load as well as a constraint that its source is a
Measured_Source which has its own attribute extensions over Source. One of
the goals here is to add that constraint enforcement. I was able to make it
work with the following hybrid_method and hybrid_method.expression, but the
isinstance(Production_Load.source, Measured_Source) enforcement is missing.
Eric
{{{
class Production_Load(Load):
__tablename__ = 'production_load'
__mapper_args__ = { 'polymorphic_identity':'production_load' }
id = Column(Integer, ForeignKey('load.id'), primary_key=True)
top = Column(Numeric, nullable=False)
bottom = Column(Numeric, nullable=False)
@hybrid_method
def delta(self):
return (self.top-self.bottom)*self.source.conversion if
self.source else None
@gdelta.expression
def delta(self):
# not sure about the performance here
return
(self.top-self.bottom)*select([Measured_Source.conversion]).where(Measured_Source.id==self.source_id).label('delta')
}}}
On Wednesday, February 12, 2014 7:17:08 AM UTC-7, Michael Bayer wrote:
On Feb 11, 2014, at 9:38 PM, Eric Atkin eat...@certusllc.us wrote:
Hi,
I want to override a relationship in a subclass to relate to a subclass
of the base attributes' related class. Perhaps an example of how I thought
it should work:
{{{
class Load(Base):
__tablename__ = 'load'
__mapper_args__ = {
'polymorphic_identity':'load',
'polymorphic_on':'polymorphic_type',
}
id = Column(Integer, primary_key=True)
polymorphic_type = Column(Text, nullable=False)
source_id = Column(Integer, ForeignKey('source.id'))
source = relationship('Source')
class Production_Load(Load):
__tablename__ = 'production_load'
__mapper_args__ = { 'polymorphic_identity':'production_load' }
id = Column(Integer, ForeignKey('load.id'), primary_key=True)
source_id = Column(Integer, ForeignKey('measured_source.id'))
source = relationship('Measured_Source')
class Source(Base):
__tablename__ = 'source'
__mapper_args__ = {
'polymorphic_identity':'source',
'polymorphic_on':'polymorphic_type',
}
id = Column(Integer, primary_key=True)
polymorphic_type = Column(Text, nullable=False)
class Measured_Source(Source):
__tablename__ = 'measured_source'
__mapper_args__ = { 'polymorphic_identity':'measured_source' }
id = Column(Integer, ForeignKey('source.id'), primary_key=True)
}}}
As you can see, we have Load.source - Source and I want
Production_Load.source - Measured_Source, but when I import the models, I
get the following warning:
{...}/env/lib/python2.7/site-packages/sqlalchemy/orm/properties.py:1028:
SAWarning: Warning: relationship 'source' on mapper
'Mapper|Production_Load|production_load' supersedes the same relationship
on inherited mapper 'Mapper|Load|load'; this can cause dependency issues
during flush
and when I try to use Production_Load.source (class level attr) in a
query, I get the following error:
AttributeError: Neither 'InstrumentedAttribute' object nor 'Comparator'
object associated with Production_Load.source has an attribute 'conversion'
Is such a thing possible, even with a re-factor of the models?
“conversion” sounds like an attribute name on your end, but generally
being able to supersede a relationship like that when the inheritance is
not “concrete” is not supported. you’d need to name it to something else.
--
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Re: [sqlalchemy] override relationship in subclass
On Feb 12, 2014, at 1:53 PM, Eric Atkin eat...@certusllc.us wrote: Yeah sorry I missed that. conversion is an attribute on Measured_Source. So the intent is that a Production_Load is a Load with its own additional attributes over Load as well as a constraint that its source is a Measured_Source which has its own attribute extensions over Source. One of the goals here is to add that constraint enforcement. I was able to make it work with the following hybrid_method and hybrid_method.expression, but the isinstance(Production_Load.source, Measured_Source) enforcement is missing. well you’d make two relationships and your hybrid method would make the choice between which one is being accessed. signature.asc Description: Message signed with OpenPGP using GPGMail
[sqlalchemy] override relationship in subclass
Hi,
I want to override a relationship in a subclass to relate to a subclass of
the base attributes' related class. Perhaps an example of how I thought it
should work:
{{{
class Load(Base):
__tablename__ = 'load'
__mapper_args__ = {
'polymorphic_identity':'load',
'polymorphic_on':'polymorphic_type',
}
id = Column(Integer, primary_key=True)
polymorphic_type = Column(Text, nullable=False)
source_id = Column(Integer, ForeignKey('source.id'))
source = relationship('Source')
class Production_Load(Load):
__tablename__ = 'production_load'
__mapper_args__ = { 'polymorphic_identity':'production_load' }
id = Column(Integer, ForeignKey('load.id'), primary_key=True)
source_id = Column(Integer, ForeignKey('measured_source.id'))
source = relationship('Measured_Source')
class Source(Base):
__tablename__ = 'source'
__mapper_args__ = {
'polymorphic_identity':'source',
'polymorphic_on':'polymorphic_type',
}
id = Column(Integer, primary_key=True)
polymorphic_type = Column(Text, nullable=False)
class Measured_Source(Source):
__tablename__ = 'measured_source'
__mapper_args__ = { 'polymorphic_identity':'measured_source' }
id = Column(Integer, ForeignKey('source.id'), primary_key=True)
}}}
As you can see, we have Load.source - Source and I want
Production_Load.source - Measured_Source, but when I import the models, I
get the following warning:
{...}/env/lib/python2.7/site-packages/sqlalchemy/orm/properties.py:1028:
SAWarning: Warning: relationship 'source' on mapper
'Mapper|Production_Load|production_load' supersedes the same relationship
on inherited mapper 'Mapper|Load|load'; this can cause dependency issues
during flush
and when I try to use Production_Load.source (class level attr) in a query,
I get the following error:
AttributeError: Neither 'InstrumentedAttribute' object nor 'Comparator'
object associated with Production_Load.source has an attribute 'conversion'
Is such a thing possible, even with a re-factor of the models?
Thanks,
Eric
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