sqlalchemy.ext.declarative.ConcreteBase

A helper class for 'concrete' declarative mappings.

.ConcreteBase will use the .polymorphic_union function automatically, against all tables mapped as a subclass to this class. The function is called via the __declare_last__() function, which is essentially a hook for the .after_configured event.

.ConcreteBase produces a mapped table for the class itself. Compare to .AbstractConcreteBase, which does not.

Example:

from sqlalchemy.ext.declarative import ConcreteBase

class Employee(ConcreteBase, Base):
    __tablename__ = 'employee'
    employee_id = Column(Integer, primary_key=True)
    name = Column(String(50))
    __mapper_args__ = {
                    'polymorphic_identity':'employee',
                    'concrete':True}

class Manager(Employee):
    __tablename__ = 'manager'
    employee_id = Column(Integer, primary_key=True)
    name = Column(String(50))
    manager_data = Column(String(40))
    __mapper_args__ = {
                    'polymorphic_identity':'manager',
                    'concrete':True}

The name of the discriminator column used by .polymorphic_union defaults to the name type. To suit the use case of a mapping where an actual column in a mapped table is already named type, the discriminator name can be configured by setting the _concrete_discriminator_name attribute:

class Employee(ConcreteBase, Base):
    _concrete_discriminator_name = '_concrete_discriminator'