python - Polymorphic identity + history_mapper -

i used history_meta extension (http://docs.sqlalchemy.org/en/latest/_modules/examples/versioned_history/history_meta.html) sqlalchemy.

the problem not seem work polymorphic identity, @ least when using multiple tables so:

class baseversion(versioned, base):     __tablename__ = 'base_version'     id = column(integer, primary_key=true)     ...     __mapper_args__ = {         'polymorphic_identity':'base_version',         'polymorphic_on':type,     } 

(note baseversion uses versioned mixin defined in history_meta)

then there's class inherits baseversion:

class unspecifiedversion(baseversion):     __tablename__ = 'unspecified_version'     id = column(integer, foreignkey('base_version.id'), primary_key=true)     related_base_version_id = column(integer, foreignkey('base_version.id'), index=true)     related_base_version = relationship('baseversion', uselist=false, foreign_keys=[related_base_version_id])     __mapper_args__ = {         'polymorphic_identity':'unspecified_version',         'inherit_condition':(related_base_version_id==baseversion.id)     } 

backend db postgres.

trying produce history table ends error:

sqlalchemy.exc.programmingerror: (psycopg2.programmingerror) there no unique constraint matching given keys referenced table "base_version_history"        [sql: ' create table unspecified_version_history (         id integer not null,         related_base_version_id integer,         version integer not null,         changed timestamp without time zone,         changed_by varchar,         primary key (id, version),         foreign key(id, related_base_version_id, version) references base_version_history (id, id, version) )  '] 

now that's weird because base_version_history table has id , version columns.

i got through same error similar. issue appears composite primary keys , composite foreign keys being generated, seen in these last 2 lines of sql:

primary key (id, version), foreign key(id, related_base_version_id, version) references base_version_history (id, id, version) 

composite foreign keys need find matching composite unique keys (basically). if table created two-column primary key, chances other 1 did too, , foreign key looking three-column unique key. also, same column twice looks wrong: (id, id, version). don't know extension working can't tell how fix it.