I am writing a multimedia archive database backend and I want to use joined table inheritance. I am using Python with SQLAlchemy with the declarative extension. The table holding the media record is as follows:
_Base = declarative_base()
class Record(_Base):
__tablename__ = 'records'
item_id = Column(String(M_ITEM_ID), ForeignKey('items.id'))
storage_id = Column(String(M_STORAGE_ID), ForeignKey('storages.id'))
id = Column(String(M_RECORD_ID), primary_key=True)
uri = Column(String(M_RECORD_URI))
type = Column(String(M_RECORD_TYPE))
name = Column(String(M_RECORD_NAME))
The column type
is a discriminator. Now I want to define the child class A
udioRecord from the Record
class, but I don't how to setup the polymorphic mapper using the declarative syntax . I am looking for an equivalent for the following code (from SQLAlchemy documentation):
mapper(Record, records, polymorphic_on=records.c.type, polymorphic_identity='record')
mapper(AudioRecord, audiorecords, inherits=Record, polymorphic_identity='audio_record')
How can I pass the polymorphic_on
, polymorphic_identity
and inherits
keywords to the mapper created by the declarative extension?
Thank you Jan
I finally found the answer in the manual.
http://www.sqlalchemy.org/docs/05/reference/ext/declarative.html#joined-table-inheritance
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