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我有以下3個SQL鍊金術車型如何在SQLAlchemy中查詢這些外鍵關係?
class MyModelA(db.Model):
a_id = db.Column(db.Integer, nullable=False, primary_key=True)
my_field1 = db.Column(db.String(1024), unique=True)
class MyModelB(db.Model):
b_id = db.Column(db.Integer, nullable=False, primary_key=True)
my_field2 = db.Column(db.String(1024), nullable=True)
def my_method(self, arg_my_field1):
pass # what goes here??
class MyModelC(db.Model, Timestamp):
c_id = db.Column(db.Integer, nullable=False, primary_key=True)
a_id = db.Column(db.Integer, db.ForeignKey(MyModelA.a_id), default=lambda: MyModelA.query.filter(MyModelA.my_field1 == 'XYZ').one().a_id)
a = db.relationship('MyModelA', backref=db.backref('my_model_c'))
b_id = db.Column(db.Integer, db.ForeignKey(MyModelB.b_id), nullable=False)
b = db.relationship('MyModelB', backref=db.backref('my_model_c'))
my_field3 = db.Column(db.String(1024), unique=True)
__table_args__ = (db.UniqueConstraint('a_id', 'b_id', name='unique_constraint_aid_bid'),)
在該方法中my_method
,我想回到的MyModelC
實例的my_field3
字段(指向self
並指向具有my_field1
的情況下,MyModelA
- 敏感匹配arg_my_field1
)。應該有最多一個這樣的例子。如果不存在這樣的MyModelC
實例,則返回None
。
我應該在my_method
中寫什麼SQLAlchemy查詢以實現該結果?