AttributeError: Neither 'QueryableAttribute' object nor 'Comparator' object has an attribute '__visit_name__'

[Dane K Barney]

I am using SQLAlchemy 1.4.2 and have been encountering this strange error message which I've managed to boil down to this minimal example:

import sqlalchemy as sa

from sqlalchemy.orm import declarative_base, relationship

Base = declarative_base()

class Parent(Base):

    __tablename__ = "parent"

    id = sa.Column(sa.Integer, primary_key=True)

class Child(Base):

    __tablename__ = "child"

    id = sa.Column(sa.Integer, primary_key=True)

    parent_id = sa.Column(sa.Integer, sa.ForeignKey("parent.id"))

    parent = relationship("Parent")

statement = sa.select([Child.id]).join(Child.parent).where(Parent.id == sa.bindparam("id"))

statement = statement.params(id=10)

The call to statement.params(...) is throwing the following stacktrace. Can anyone tell me what I'm doing wrong?

Traceback (most recent call last):

  File "test_sqlalchemy_error.py", line 20, in <module>

    statement = statement.params(id=10)

  File ".venv/lib/python3.7/site-packages/sqlalchemy/sql/elements.py", line 346, in params

    return self._replace_params(False, optionaldict, kwargs)

  File ".venv/lib/python3.7/site-packages/sqlalchemy/sql/elements.py", line 363, in _replace_params

    return cloned_traverse(self, {}, {"bindparam": visit_bindparam})

  File ".venv/lib/python3.7/site-packages/sqlalchemy/sql/visitors.py", line 742, in cloned_traverse

    obj = clone(obj, deferred_copy_internals=deferred_copy_internals)

  File ".venv/lib/python3.7/site-packages/sqlalchemy/sql/visitors.py", line 735, in clone

    newelem._copy_internals(clone=clone, **kw)

  File ".venv/lib/python3.7/site-packages/sqlalchemy/sql/selectable.py", line 5208, in _copy_internals

    clone=clone, omit_attrs=("_from_obj",), **kw

  File ".venv/lib/python3.7/site-packages/sqlalchemy/sql/traversals.py", line 718, in _copy_internals

    result = meth(attrname, self, obj, **kw)

  File ".venv/lib/python3.7/site-packages/sqlalchemy/sql/traversals.py", line 777, in visit_setup_join_tuple

    for (target, onclause, from_, flags) in element

  File ".venv/lib/python3.7/site-packages/sqlalchemy/sql/traversals.py", line 777, in <genexpr>

    for (target, onclause, from_, flags) in element

  File ".venv/lib/python3.7/site-packages/sqlalchemy/sql/visitors.py", line 736, in clone

    meth = visitors.get(newelem.__visit_name__, None)

  File ".venv/lib/python3.7/site-packages/sqlalchemy/orm/attributes.py", line 308, in __getattr__

    replace_context=err,

  File ".venv/lib/python3.7/site-packages/sqlalchemy/util/compat.py", line 198, in raise_

    raise exception

AttributeError: Neither 'QueryableAttribute' object nor 'Comparator' object associated with Child.parent has an attribute '__visit_name__'

[Mike Bayer]

hi -

that's a bug!    The .params() method is kind of forgotten.     https://github.com/sqlalchemy/sqlalchemy/issues/6124 is added, however this is not a regression since this is using new functionality on select().   I think I have a fairly straightforward fix for this however it won't be in SQLAlchemy 1.4.3, which needs to go out very soon.

For now I would advise sending the params directly to the session.execute() method.

--

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The Python SQL Toolkit and Object Relational Mapper

 

http://www.sqlalchemy.org/

 

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