[Sqlalchemy-tickets] Issue #3531: bind param replacement in join_condition() doesn't work for type_coerce (zzzeek/sqlalchemy)

[Mike B. <iss...@bi...>]

New issue 3531: bind param replacement in join_condition() doesn't work for type_coerce
https://bitbucket.org/zzzeek/sqlalchemy/issues/3531/bind-param-replacement-in-join_condition

Mike Bayer:

type_coerce makes its decision about the thing it is processing when created.  if a bindparam, the type is changed.  otherwise, a label() is produced.  

However this fails for this :


```
#!python

from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()


class CastToIntegerType(TypeDecorator):
    impl = String

    def column_expression(self, col):
        return cast(col, Integer)

    def bind_expression(self,col):
        return cast(col, String)

class Person(Base):
    __tablename__ = 'person'
    id = Column('id_string', CastToIntegerType, primary_key=True)

    pets = relationship('Pets',
        primaryjoin='foreign(Pets.person_id)==type_coerce(Person.id, Integer)')

class Pets(Base):
    __tablename__ = 'pets'
    id = Column('id', Integer, primary_key=True)
    person_id = Column('person_id', Integer, ForeignKey('person.id_string'), primary_key=True)


e = create_engine("sqlite://", echo=True)
Base.metadata.create_all(e)

s = Session(e)
s.add_all([Person(id="5", pets=[Pets(id="1")])])
s.commit()

p1 = s.query(Person).first()
p1.pets

```

because we are creating bindparam after the fact - there's no actual TypeCoerce construct here so when we see that Label, we don't know anything that there was a type coerce.  We'd need to build some new construct.