join, the query will not find anything to join for the NULL and return blank for theParentName...
__tablename__ ='parent'id= Column(Integer, primary_key=True) children = relationship("Child", uselist=False, backref='parent')# 在父表类中通过 relationship() 方法来引用子表的类集合classChild(Base): __tablename__ ='child'id= Column(Integer, primary_key=True) parent_id = Column(Integer...
REFERENCES parent-table-name (,column-namePERIODBUSINESS_TIME)ON DELETERESTRICTNO ACTIONCASCADESET NULLENFORCEDNOT ENFORCED ENABLE QUERY OPTIMIZATION check-constraint: CONSTRAINTconstraint-name CHECK ( check-condition) partitioning-clause: (,partition-expression)(,partition-element) partition-expression: ...
backref 只需要在 Parent 类中声明 children,Child.parent 会被动态创建。 back_populates 必须在两个类中显式地使用 back_populates,更显繁琐,理解更直观 relationship 使用 relationship 函数是 sqlalchemy对关系之间提供的一种便利的调用方式, backref参数则对关系提供反向引用的声明。 from sqlalchemy.ext.declarativ...
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In the EMP_DEPT_CHECK trigger (see "Foreign Key Trigger for Child Table"), the row that contains the referenced parent key value is locked to guarantee that it remains for the duration of the transaction; if the parent key is updated or deleted, referential integrity would be violated....
backref 只需要在 Parent 类中声明 children,Child.parent 会被动态创建。 back_populates 必须在两个类中显式地使用 back_populates,更显繁琐,理解更直观 relationship 使用 relationship 函数是 sqlalchemy对关系之间提供的一种便利的调用方式, backref参数则对关系提供反向引用的声明。
classChild(Base):__tablename__='child'id=Column(Integer,primary_key=True)parent_id=Column(Integer,ForeignKey('parent.id'))parent=relationship("Parent",back_populates="children")# 子表类中附加一个 relationship() 方法# 并且在(父)子表类的 relationship() 方法中使用 relationship.back_populates ...
Parent/childWhen you use the parent/child approach, each row contains a reference to the parent. The following table defines a typical table used to contain the parent and the child rows in a parent/child relationship:SQL კოპირება ...
Specifies what action happens to rows in the table created, if those rows have a referential relationship and the referenced row is deleted from the parent table. The default is NO ACTION. NO ACTION The Database Engine raises an error and the delete action on the row in the parent table ...