<http://stackoverflow.com/questions/19716518/sqlalchemy-many-to-many-table-with-multiple-foreign-key-entires#>
I'm new with sqlalchemy and I want to do this as simply as possible, yet
correctly. I want to track domain use across multiple companies on a
monthly basis, so I set up the following tables:
class Company(Base):
__tablename__ = 'company'
id = Column(Integer, primary_key = True)
name = Column('name', String)
class Domains(Base):
__tablename__ = 'domains'
id = Column(Integer, primary_key=True)
name = Column('name', String, unique=True)
class MonthlyUsage(Base):
'''
Track domain usage across all
companies on a monthly basis.
'''
__tablename__ = 'monthlyusage'
month = Column(DateTime)
company_id = Column(Integer, ForeignKey('company.id'))
domain_id = Column(Integer, ForeignKey('domains.id'))
# <...other columns snipped out...>
company = relationship('Company', backref='company_assoc')
domain = relationship('Domains', backref='domain_assoc')
This works fine, until I add usage details for the second month. Then I get
duplicate key value errors:
*sqlalchemy.exc.IntegrityError: (IntegrityError) duplicate key value
violates unique constraint "monthlyusage_pkey"*
Does this mean I have to split out the "monthlyusage" into another m2m
table? That seems unnecessarily complicated, since all that needs to be
unique is the month, company_id, and domain_id fields.
Any suggestions for my layout here, to keep it as simple as possible, yet
still correct?
Thanks!
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