python – SQLAlchemy可以在不查询数据库的情况下填充外键关系吗

A key feature to enable management of a large collection is the so-called “dynamic” relationship. This is an optional form of relationship() which returns a Query object in place of a collection when accessed. filter() criterion may be applied as well as limits and offsets,either explicitly or via array slices:

示例表：

class Parent(Base):
    __tablename__ = 'parent'
    id = Column(Integer,primary_key=True)
    children = relationship("Child",lazy="dynamic")

class Child(Base):
    __tablename__ = 'child'
    id = Column(Integer,primary_key=True)
    parent_id = Column(Integer,ForeignKey('parent.id'))

加载Parent对象时,不会加载子对象;相反,将在其位置加载Query对象,如果需要,可以使用它来访问子对象.

p = session.query(Parent).first() # children will not be loaded here
print(type(p.children)) # <class 'sqlalchemy.orm.dynamic.AppenderQuery'>
all_children = p.children.all() # conduct a query on the children query object
print(all_children) # [<__main__.Child object at 0x10ba3f908>,<__main__.Child object at 0x10ba3f978>]