modernize and repair inheritance examples

remarkably, the examples for concrete and single were still
using classical mappings.    Ensure all three examples use
modern declarative patterns, each illustrate the identical set
of query operations.  Use back_populates, flat=True for joins,
etc. ensure flake8 linting, correct links and add a link back
from newly reworked inheritance documentation.

Change-Id: I8465a9badbb0eda804f457ccac599f051ee3c27c

1 files changed, 140 insertions, 53 deletions

diff --git a/examples/inheritance/concrete.py b/examples/inheritance/concrete.py
index f9bdc81b4..258f41025 100644
--- a/examples/inheritance/concrete.py
+++ b/examples/inheritance/concrete.py
@@ -1,74 +1,161 @@
-"""Concrete (table-per-class) inheritance example."""
+"""Concrete-table (table-per-class) inheritance example."""
 
-from sqlalchemy import create_engine, MetaData, Table, Column, Integer, \
-    String
-from sqlalchemy.orm import mapper, sessionmaker, polymorphic_union
+from sqlalchemy import Column, Integer, String, \
+    ForeignKey, create_engine, inspect, or_
+from sqlalchemy.orm import relationship, Session, with_polymorphic
+from sqlalchemy.ext.declarative import declarative_base
+from sqlalchemy.ext.declarative import ConcreteBase
 
-metadata = MetaData()
 
-managers_table = Table('managers', metadata,
-    Column('employee_id', Integer, primary_key=True),
-    Column('name', String(50)),
-    Column('manager_data', String(40))
-)
+Base = declarative_base()
 
-engineers_table = Table('engineers', metadata,
-    Column('employee_id', Integer, primary_key=True),
-    Column('name', String(50)),
-    Column('engineer_info', String(40))
-)
 
-engine = create_engine('sqlite:///', echo=True)
-metadata.create_all(engine)
+class Company(Base):
+    __tablename__ = 'company'
+    id = Column(Integer, primary_key=True)
+    name = Column(String(50))
 
+    employees = relationship(
+        "Person",
+        back_populates='company',
+        cascade='all, delete-orphan')
 
-class Employee(object):
-    def __init__(self, name):
-        self.name = name
     def __repr__(self):
-        return self.__class__.__name__ + " " + self.name
+        return "Company %s" % self.name
 
-class Manager(Employee):
-    def __init__(self, name, manager_data):
-        self.name = name
-        self.manager_data = manager_data
-    def __repr__(self):
-        return self.__class__.__name__ + " " + \
-                    self.name + " " +  self.manager_data
 
-class Engineer(Employee):
-    def __init__(self, name, engineer_info):
-        self.name = name
-        self.engineer_info = engineer_info
+class Person(ConcreteBase, Base):
+    __tablename__ = 'person'
+    id = Column(Integer, primary_key=True)
+    company_id = Column(ForeignKey('company.id'))
+    name = Column(String(50))
+
+    company = relationship("Company", back_populates="employees")
+
+    __mapper_args__ = {
+        'polymorphic_identity': 'person',
+    }
+
     def __repr__(self):
-        return self.__class__.__name__ + " " + \
-                    self.name + " " +  self.engineer_info
+        return "Ordinary person %s" % self.name
+
+
+class Engineer(Person):
+    __tablename__ = 'engineer'
+    id = Column(Integer, primary_key=True)
+    name = Column(String(50))
+    company_id = Column(ForeignKey('company.id'))
+    status = Column(String(30))
+    engineer_name = Column(String(30))
+    primary_language = Column(String(30))
 
+    company = relationship("Company", back_populates="employees")
 
-pjoin = polymorphic_union({
-    'manager':managers_table,
-    'engineer':engineers_table
-}, 'type', 'pjoin')
+    __mapper_args__ = {
+        'polymorphic_identity': 'engineer',
+        'concrete': True
+    }
 
-employee_mapper = mapper(Employee, pjoin, polymorphic_on=pjoin.c.type)
-manager_mapper = mapper(Manager, managers_table,
-                        inherits=employee_mapper, concrete=True,
-                        polymorphic_identity='manager')
-engineer_mapper = mapper(Engineer, engineers_table,
-                         inherits=employee_mapper, concrete=True,
-                         polymorphic_identity='engineer')
+    def __repr__(self):
+        return (
+            "Engineer %s, status %s, engineer_name %s, "
+            "primary_language %s" %
+            (
+                self.name, self.status,
+                self.engineer_name, self.primary_language)
+        )
+
+
+class Manager(Person):
+    __tablename__ = 'manager'
+    id = Column(Integer, primary_key=True)
+    name = Column(String(50))
+    company_id = Column(ForeignKey('company.id'))
+    status = Column(String(30))
+    manager_name = Column(String(30))
+
+    company = relationship("Company", back_populates="employees")
+
+    __mapper_args__ = {
+        'polymorphic_identity': 'manager',
+        'concrete': True
+    }
+
+    def __repr__(self):
+        return "Manager %s, status %s, manager_name %s" % (
+            self.name, self.status, self.manager_name)
+
+
+engine = create_engine('sqlite://', echo=True)
+Base.metadata.create_all(engine)
+
+session = Session(engine)
+
+c = Company(name='company1', employees=[
+    Manager(
+        name='pointy haired boss',
+        status='AAB',
+        manager_name='manager1'),
+    Engineer(
+        name='dilbert',
+        status='BBA',
+        engineer_name='engineer1',
+        primary_language='java'),
+    Person(name='joesmith'),
+    Engineer(
+        name='wally',
+        status='CGG',
+        engineer_name='engineer2',
+        primary_language='python'),
+    Manager(
+        name='jsmith',
+        status='ABA',
+        manager_name='manager2')
+])
+session.add(c)
+
+session.commit()
 
+c = session.query(Company).get(1)
+for e in c.employees:
+    print(e, inspect(e).key, e.company)
+assert set([e.name for e in c.employees]) == set(
+    ['pointy haired boss', 'dilbert', 'joesmith', 'wally', 'jsmith'])
+print("\n")
 
-session = sessionmaker(engine)()
+dilbert = session.query(Person).filter_by(name='dilbert').one()
+dilbert2 = session.query(Engineer).filter_by(name='dilbert').one()
+assert dilbert is dilbert2
 
-m1 = Manager("pointy haired boss", "manager1")
-e1 = Engineer("wally", "engineer1")
-e2 = Engineer("dilbert", "engineer2")
+dilbert.engineer_name = 'hes dilbert!'
 
-session.add(m1)
-session.add(e1)
-session.add(e2)
 session.commit()
 
-print(session.query(Employee).all())
+c = session.query(Company).get(1)
+for e in c.employees:
+    print(e)
+
+# query using with_polymorphic.
+eng_manager = with_polymorphic(Person, [Engineer, Manager])
+print(
+    session.query(eng_manager).
+    filter(
+        or_(
+            eng_manager.Engineer.engineer_name == 'engineer1',
+            eng_manager.Manager.manager_name == 'manager2'
+        )
+    ).all()
+)
+
+# illustrate join from Company
+eng_manager = with_polymorphic(Person, [Engineer, Manager])
+print(
+    session.query(Company).
+    join(
+        Company.employees.of_type(eng_manager)
+    ).filter(
+        or_(eng_manager.Engineer.engineer_name == 'engineer1',
+            eng_manager.Manager.manager_name == 'manager2')
+    ).all())
 
+session.commit()