I have 2 tables Person (id, name) & Employee (id, salary) and every
Employee 'isa' Person, so employee.id == person.id. I am trying to use
the Concrete Inheritance (i.e. ' pjoin) example provided in the
documentation. My mapping looks as follows.
person_table = Table("persons", __meta__,
Column("id", Integer, primary_key=True),
Column("name", String(80))
)
employee_table = Table("empys", __meta__,
Column("id", Integer, ForeignKey("persons.id"),
primary_key=True),
Column("salary", Integer),
)
class Person (object): pass
class Employee(Person): pass
pjoin = polymorphic_union({
'person':person_table,
'employee':employee_table
}, 'type', 'pjoin')
person_mapper = mapper(Person, person_table, select_table=pjoin, \
polymorphic_on=pjoin.c.type,
polymorphic_identity='person')
emp_mapper = mapper(Employee, employee_table, inherits=person_mapper,
\
concrete=True, polymorphic_identity='employee')
I want to now add a New employee to the system with the following
snippet.
e = Employee()
e.name = 'TestEmpl'
e.salary = 100
session.save(e)
session.commit()
Problem is when it tries to save employee, sqlalchemy raises the
following error
"""
sqlalchemy.exceptions.ProgrammingError: (ProgrammingError) relation
"empys_id_seq" does not exist
'select nextval(\'"empys_id_seq"\')' None
"""
Since all id's in employees table map directly to Person table (which
has the correct sequence), I would think alchemy would first store the
"Person" part and then store the "employee" part. Any clues on how to
correct this ??.
I also tried adding a Sequence to employee forcing it to use the same
one as person table...
employee_table = Table("empys", __meta__,
Column("id", Integer, ForeignKey("persons.id"),
Sequence("person_id_seq") primary_key=True),
Column("salary", Integer),
)
But now it raises a constraint violation because its trying to insert
a row in employees table without inserting anything in person first..
Any ideas how I can fix this?.. I would greatly appreciate any help in
this regard.. Thanks
Partha
Here is the full program.. Thanks..
from sqlalchemy import create_engine, MetaData, Table, Column, types,
Sequence
from sqlalchemy import Table, Column, Integer, String, DECIMAL,
Numeric, ForeignKey, DateTime, Boolean, CHAR
from sqlalchemy.orm import mapper,sessionmaker, relation,
polymorphic_union
__meta__ = MetaData()
person_table = Table("persons", __meta__,
Column("id", Integer, primary_key=True),
Column("name", String(80))
)
employee_table = Table("empys", __meta__,
Column("id", Integer, ForeignKey("persons.id"),
primary_key=True),
Column("salary", Integer),
)
class Person (object): pass
class Employee(Person): pass
pjoin = polymorphic_union({
'person':person_table,
'employee':employee_table
}, 'type', 'pjoin')
person_mapper = mapper(Person, person_table, select_table=pjoin, \
polymorphic_on=pjoin.c.type,
polymorphic_identity='person')
emp_mapper = mapper(Employee, employee_table, inherits=person_mapper,
\
concrete=True, polymorphic_identity='employee')
engine = create_engine('postgres:///test?user=postgres&password=foo',
echo=True)
session = sessionmaker(autoflush=True, bind = engine,
transactional=True)()
def refresh(engine = engine):
__meta__.drop_all(engine)
__meta__.create_all(engine)
def main():
refresh()
e = Employee()
e.name = 'TestEmpl'
e.salary = 100
session.save(e)
session.commit()
if __name__ == '__main__':
main()
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