Single table inheritance attributes are not hidden correctly when mixed with joined table inheritance

[Jack Zhou]

When mixing single table inheritance and joined table inheritance like this:

class Person(Base):
    __tablename__ = "person"

    id = Column(Integer, primary_key=True)
    type = Column(String)

    __mapper_args__ = {
        "polymorphic_on": type,
    }


class Contractor(Person):
    contractor_field = Column(String)

    __mapper_args__ = {
        "polymorphic_identity": "contractor",
    }


class Employee(Person):
    __tablename__ = "employee"

    id = Column(Integer, ForeignKey(Person.id), primary_key=True)


class Engineer(Employee):
    __mapper_args__ = {
        "polymorphic_identity": "engineer",
    }

instances of Engineer has access to contractor_field:

try:
    Employee().contractor_field
except AttributeError:
    pass  # correctly raises
else:
    assert False
try:
    Engineer().contractor_field
except AttributeError:
    pass
else:
    assert False  # doesn't raise!

[Mike Bayer]

it looks like this is handled in declarative

diff --git a/lib/sqlalchemy/ext/declarative/base.py b/lib/sqlalchemy/ext/declarative/base.py
index 16cb05e..7d97c1c 100644
--- a/lib/sqlalchemy/ext/declarative/base.py
+++ b/lib/sqlalchemy/ext/declarative/base.py
@@ -492,8 +492,11 @@ class _MapperConfig(object):

             if 'exclude_properties' not in mapper_args:
                 mapper_args['exclude_properties'] = exclude_properties = \
-                    set([c.key for c in inherited_table.c
-                         if c not in inherited_mapper._columntoproperty])
+                    set(
+                    [c.key for c in inherited_table.c
+                     if c not in inherited_mapper._columntoproperty]
+                ).union(inherited_mapper.exclude_properties or ())
+
                 exclude_properties.difference_update(
                     [c.key for c in self.declared_columns])

if mapping w/ classical mappings, the "contractor_field" will leak into Person if not added to exclude_properties explicitly because it needs to be in the Table that you map to Person, and there's no indication that contractor_field is only for Contractor and not Person otherwise, so the whole "properties are excluded automatically" thing is a declarative feature.

[Mike Bayer]

https://gerrit.sqlalchemy.org/301

[Mike Bayer]

Union the exclude_properties of the inheriting mapper in declarative

Fixed bug where the "automatic exclude" feature of declarative that ensures a column local to a single table inheritance subclass does not appear as an attribute on other derivations of the base would not take effect for multiple levels of subclassing from the base.

Change-Id: Ibf67b631b4870dd1bd159f7d6085549d299fffe0 Fixes: #3895

→ <<cset 9a5943bf76cd>>