hey there.
The warnings go away entirely by making Parent.children viewonly=True, which
for this type of mapping is recommended:
class Parent(Base):
__tablename__ = "left"
id = Column(Integer, primary_key=True)
children = relationship(
"Child", secondary=Association.__table__, backref="parents",
viewonly=True
)
you wouldn't want to append new records to Parent.children because that would
create invalid Association rows (missing extra_data).
The warning box at the end of
https://docs.sqlalchemy.org/en/14/orm/basic_relationships.html#association-object
discusses this situation and the desirability of making the relationship which
includes "secondary" as viewonly=True.
hope this helps
On Wed, Mar 9, 2022, at 8:09 PM, Michael Merickel wrote:
> Sorry for the rambling, it's been difficult for me to figure out what
> question to ask because I'm so confused. Below is the minimum viable example
> that produces no warnings with respect to the overlaps flags and I cannot
> explain hardly any of them. For example, why does Child.parents require
> "child_links,parent,child"? 3 values that seem to be somewhat unrelated and
> are at the very least definitely on different models?
>
> class Association(Base):
> __tablename__ = 'association'
> left_id = Column(ForeignKey('left.id'), primary_key=True)
> right_id = Column(ForeignKey('right.id'), primary_key=True)
> extra_data = Column(String(50))
>
> parent = relationship('Parent', back_populates='child_links')
> child = relationship('Child', back_populates='parent_links')
>
> class Parent(Base):
> __tablename__ = 'left'
> id = Column(Integer, primary_key=True)
>
> children = relationship(
> 'Child',
> secondary=Association.__table__,
> back_populates='parents',
> overlaps='child,parent',
> )
> child_links = relationship(
> 'Association',
> back_populates='parent',
> overlaps='children',
> )
>
> class Child(Base):
> __tablename__ = 'right'
> id = Column(Integer, primary_key=True)
>
> parents = relationship(
> 'Parent',
> secondary=Association.__table__,
> back_populates='children',
> overlaps='child_links,parent,child',
> )
> parent_links = relationship(
> 'Association',
> back_populates='child',
> overlaps='children,parents',
> )
>
>
> On Wed, Mar 9, 2022 at 4:50 PM Michael Merickel <[email protected]> wrote:
>> I think ultimately I want the overlaps config but reading through
>> https://docs.sqlalchemy.org/en/14/errors.html#relationship-x-will-copy-column-q-to-column-p-which-conflicts-with-relationship-s-y
>> it doesn't make any sense to me what the values in the overlaps= argument
>> are referring to. For example in last snippet that was simpler, what is
>> overlaps='parent' referring to? Neither the Parent object, nor the Child
>> object has something named "parent" so other than blinding trusting the
>> warning I'm unclear how to see what the mapper is building that conflicts
>> here.
>>
>> On Wed, Mar 9, 2022 at 4:33 PM Michael Merickel <[email protected]> wrote:
>>> It's probably worth noting I can narrow it down to a single warning with
>>> the following snippet and it's still unclear to me how to resolve this:
>>>
>>> class Association(Base):
>>> __tablename__ = 'association'
>>> left_id = Column(ForeignKey('left.id'), primary_key=True)
>>> right_id = Column(ForeignKey('right.id'), primary_key=True)
>>> extra_data = Column(String(50))
>>>
>>> parent = relationship('Parent')
>>>
>>> class Parent(Base):
>>> __tablename__ = 'left'
>>> id = Column(Integer, primary_key=True)
>>> children = relationship('Child', secondary=Association.__table__)
>>>
>>> class Child(Base):
>>> __tablename__ = 'right'
>>> id = Column(Integer, primary_key=True)
>>>
>>>> foo.py:24: SAWarning: relationship 'Parent.children' will copy column
>>>> left.id to column association.left_id, which conflicts with
>>>> relationship(s): 'Association.parent' (copies left.id to
>>>> association.left_id). If this is not the intention, consider if these
>>>> relationships should be linked with back_populates, or if viewonly=True
>>>> should be applied to one or more if they are read-only. For the less
>>>> common case that foreign key constraints are partially overlapping, the
>>>> orm.foreign() annotation can be used to isolate the columns that should be
>>>> written towards. To silence this warning, add the parameter
>>>> 'overlaps="parent"' to the 'Parent.children' relationship. (Background on
>>>> this error at: https://sqlalche.me/e/14/qzyx)
>>>
>>> On Wed, Mar 9, 2022 at 4:31 PM Michael Merickel <[email protected]> wrote:
>>>> I have looked at the couple examples in the docs (many-to-many, and
>>>> association table) and have noticed that my codebase has a slightly
>>>> different pattern which is causing warnings when upgrading to 1.4. I'm
>>>> trying to figure out the best pattern to accomplish what I've been doing
>>>> which doesn't match the docs exactly.
>>>>
>>>> In the below example you can see that there are backrefs on all of the
>>>> links, and that there are backrefs from the link table to the related
>>>> objects, as well as a secondary link from Parent to Child via
>>>> Parent.children and Child.parents.
>>>>
>>>> There seem to be several options and I'm struggling to figure out what the
>>>> solution should be to maintain the behavior with all of the following
>>>> relationships working:
>>>>
>>>> - Parent.children
>>>> - Parent.child_links
>>>> - Child.parents
>>>> - Child.parent_links
>>>> - Association.parent
>>>> - Association.child
>>>>
>>>> Code and warnings are below:
>>>>
>>>> from sqlalchemy import Column, ForeignKey, String, Integer
>>>> from sqlalchemy.orm import configure_mappers, relationship
>>>> from sqlalchemy.ext.declarative import declarative_base
>>>>
>>>> Base = declarative_base()
>>>>
>>>> class Association(Base):
>>>> __tablename__ = 'association'
>>>> left_id = Column(ForeignKey('left.id'), primary_key=True)
>>>> right_id = Column(ForeignKey('right.id'), primary_key=True)
>>>> extra_data = Column(String(50))
>>>>
>>>> parent = relationship('Parent', backref='child_links')
>>>> child = relationship('Child', backref='parent_links')
>>>>
>>>> class Parent(Base):
>>>> __tablename__ = 'left'
>>>> id = Column(Integer, primary_key=True)
>>>> children = relationship('Child', secondary=Association.__table__,
>>>> backref='parents')
>>>>
>>>> class Child(Base):
>>>> __tablename__ = 'right'
>>>> id = Column(Integer, primary_key=True)
>>>>
>>>> configure_mappers()
>>>>
>>>>> foo.py:25: SAWarning: relationship 'Child.parents' will copy column
>>>>> right.id to column association.right_id, which conflicts with
>>>>> relationship(s): 'Association.child' (copies right.id to
>>>>> association.right_id), 'Child.parent_links' (copies right.id to
>>>>> association.right_id). If this is not the intention, consider if these
>>>>> relationships should be linked with back_populates, or if viewonly=True
>>>>> should be applied to one or more if they are read-only. For the less
>>>>> common case that foreign key constraints are partially overlapping, the
>>>>> orm.foreign() annotation can be used to isolate the columns that should
>>>>> be written towards. To silence this warning, add the parameter
>>>>> 'overlaps="child,parent_links"' to the 'Child.parents' relationship.
>>>>> (Background on this error at: https://sqlalche.me/e/14/qzyx)
>>>>> configure_mappers()
>>>>> foo.py:25: SAWarning: relationship 'Child.parents' will copy column
>>>>> left.id to column association.left_id, which conflicts with
>>>>> relationship(s): 'Association.parent' (copies left.id to
>>>>> association.left_id), 'Parent.child_links' (copies left.id to
>>>>> association.left_id). If this is not the intention, consider if these
>>>>> relationships should be linked with back_populates, or if viewonly=True
>>>>> should be applied to one or more if they are read-only. For the less
>>>>> common case that foreign key constraints are partially overlapping, the
>>>>> orm.foreign() annotation can be used to isolate the columns that should
>>>>> be written towards. To silence this warning, add the parameter
>>>>> 'overlaps="child_links,parent"' to the 'Child.parents' relationship.
>>>>> (Background on this error at: https://sqlalche.me/e/14/qzyx)
>>>>> configure_mappers()
>>>>> foo.py:25: SAWarning: relationship 'Parent.children' will copy column
>>>>> left.id to column association.left_id, which conflicts with
>>>>> relationship(s): 'Association.parent' (copies left.id to
>>>>> association.left_id), 'Parent.child_links' (copies left.id to
>>>>> association.left_id). If this is not the intention, consider if these
>>>>> relationships should be linked with back_populates, or if viewonly=True
>>>>> should be applied to one or more if they are read-only. For the less
>>>>> common case that foreign key constraints are partially overlapping, the
>>>>> orm.foreign() annotation can be used to isolate the columns that should
>>>>> be written towards. To silence this warning, add the parameter
>>>>> 'overlaps="child_links,parent"' to the 'Parent.children' relationship.
>>>>> (Background on this error at: https://sqlalche.me/e/14/qzyx)
>>>>> configure_mappers()
>>>>> foo.py:25: SAWarning: relationship 'Parent.children' will copy column
>>>>> right.id to column association.right_id, which conflicts with
>>>>> relationship(s): 'Association.child' (copies right.id to
>>>>> association.right_id), 'Child.parent_links' (copies right.id to
>>>>> association.right_id). If this is not the intention, consider if these
>>>>> relationships should be linked with back_populates, or if viewonly=True
>>>>> should be applied to one or more if they are read-only. For the less
>>>>> common case that foreign key constraints are partially overlapping, the
>>>>> orm.foreign() annotation can be used to isolate the columns that should
>>>>> be written towards. To silence this warning, add the parameter
>>>>> 'overlaps="child,parent_links"' to the 'Parent.children' relationship.
>>>>> (Background on this error at: https://sqlalche.me/e/14/qzyx)
>>>>> configure_mappers()
>>>>
>>>> Thanks!
>>>>
>>>> --
>>>>
>>>> Michael
>>>
>>>
>>> --
>>>
>>> Michael
>>
>>
>> --
>>
>> Michael
>
>
> --
>
> Michael
>
>
> --
> SQLAlchemy -
> The Python SQL Toolkit and Object Relational Mapper
>
> http://www.sqlalchemy.org/
>
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SQLAlchemy -
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http://www.sqlalchemy.org/
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