sqlalchemy.exc.InvalidRequestError：SQL表達式，列，或映射實體預期

Question

我遇到了這個sqlachemy錯誤，我一直無法理解：

sqlalchemy.exc.InvalidRequestError: SQL expression, column, or mapped entity expected - got '<class '__main__.JobRecord'>' 

這個錯誤是什麼意思？什麼是可能的原因？

這是觸發錯誤的方法：

@classmethod 
def find_job_record_from_pk(cls, pk): 
    ''' 
    return the job record with the given pk 
    ''' 
    job_record = MlcDb.get_session().query(cls).filter(cls.pk == pk).first() 
    return job_record 

映射：

@classmethod 
def define_mapping(cls): 
    ''' 
    SQLAlchemy mapping definition 
    ''' 
    cls.mapper = mapper(cls, cls.table, 
     polymorphic_on = cls.table.c.item_type, 
     properties = { 
     'item_type': synonym('_JobRecord__item_type', map_column=True), 
     'version': synonym('_JobRecord__version', map_column=True), 
     'state': synonym('_JobRecord__state', map_column=True), 
     'date_created' : synonym('_JobRecord__date_created', map_column=True) } 
    ) 

Answer 1

嘗試filter_by(pk = pk)代替