語法使用ORM中的關系查詢另一個表？

Question

該模型是這樣的（在SQLAlchemy中）：

Class Cell(Base):
    __tablename__ = "cell"
    id = Column(Integer)
    name = Column(String)

Class Sample(Base):
    __tablename__ =  "cell"
    id = Column(Integer)
    factor_id = Column(Integer, ForeignKey("cell.id"))
    cell = relationship(Cell, backref = 'sample', order_by = "Cell.id")

當我執行這樣的查詢時：

DBSession.query(Sample).filter(Sample.cell.name == "a_string")

它將引發如下異常：

File "build/bdist.linux-x86_64/egg/sqlalchemy/orm/attributes.py", line 139, in __getattr__
key)
AttributeError: Neither 'InstrumentedAttribute' object nor 'Comparator' object has an attribute  'name'

似乎Sample類中的cell字段沒有名為name的字段。 然后，如何在帶有cell字段的Sample類中查詢Cell.name ？ 有人對此有想法嗎？

謝謝！

Answer 1

有多種方法可以實現：

1.使用join（...）-我會選擇這種情況

qry = session.query(Sample).join(Cell).filter(Cell.name == "a_string")

>> SELECT sample.id AS sample_id, sample.factor_id AS sample_factor_id
>> FROM sample JOIN cell ON cell.id = sample.factor_id
>> WHERE cell.name = :name_1

2.使用any / has（...）-這將使用子查詢

qry = session.query(Sample).filter(Sample.cell.has(Cell.name == "a_string"))

>> SELECT sample.id AS sample_id, sample.factor_id AS sample_factor_id
>> FROM sample
>> WHERE EXISTS (SELECT 1
>> FROM cell
>> WHERE cell.id = sample.factor_id AND cell.name = :name_1)