如何查询多个多态继承表的关系？

Question

假设您有以下简化示例模式,它使用SQLAlchemy加入表多态继承.Engineer和Analyst模特有Role关系.该Intern模型没有.

class Role(db.Model):

    __tablename__ = 'role'

    id = db.Column(db.Integer, primary_key=True)

    name = db.Column(db.String(16), index=True)

class EmployeeBase(db.Model):

    __tablename__ = 'employee_base'

    id = db.Column(db.Integer, primary_key=True)

    some_attr = db.Column(db.String(16))
    another_attr = db.Column(db.String(16))

    type = db.Column(db.String(50), index=True)

    __mapper_args__ = {
        'polymorphic_identity': 'employee',
        'polymorphic_on': type
    }

class Engineer(EmployeeBase):

    __tablename__ = 'engineer'

    id = db.Column(db.Integer, db.ForeignKey('employee_base.id'), primary_key=True)

    role_id = db.Column(db.Integer, db.ForeignKey('role.id'), index=True)
    role = db.relationship('Role', backref='engineers')

    __mapper_args__ = {
        'polymorphic_identity': 'engineer',
    }

class Analyst(EmployeeBase):

    __tablename__ = 'analyst'

    id = db.Column(db.Integer, db.ForeignKey('employee_base.id'), primary_key=True)

    role_id = db.Column(db.Integer, db.ForeignKey('role.id'), index=True)
    role = db.relationship('Role', backref='analysts')

    __mapper_args__ = {
        'polymorphic_identity': 'analyst',
    }

class Intern(EmployeeBase):

    __tablename__ = 'intern'

    id = db.Column(db.Integer, db.ForeignKey('employee_base.id'), primary_key=True)

    term_ends = db.Column(db.DateTime, index=True, nullable=False)

    __mapper_args__ = {
        'polymorphic_identity': 'intern',
    }

如果我想找到Employees一个Role name在名称中有"石油"的地方,我会怎么做呢？

我尝试了很多很多方法.我最接近的是这个,它只返回Analyst匹配:

employee_role_join = with_polymorphic(EmployeeBase, 
    [Engineer, Analyst])
results = db.session.query(employee_role_join).join(Role).filter(Role.name.ilike('%petroleum%'))

如果我尝试做这样的事情,我得到一个AttributeError,因为我正在搜索连接Role表的属性:

employee_role_join = with_polymorphic(EmployeeBase, 
    [Engineer, Analyst])
results = db.session.query(employee_role_join).filter(or_(
    Engineer.role.name.ilike('%petroleum%'),
    Analyst.role.name.ilike('%petroleum%')))

Answer 1

您可以尝试显式指定 join ON 子句，因为第一个查询的问题似乎是Role仅在列上联接analyst.role_id：

employee_role_join = with_polymorphic(EmployeeBase, [Engineer, Analyst])
results = session.query(employee_role_join).join(Role).filter(Role.name.ilike('%petroleum%'))
print(str(results))

SELECT employee_base.id AS employee_base_id,
    employee_base.some_attr AS employee_base_some_attr,
    employee_base.another_attr AS employee_base_another_attr,
    employee_base.type AS employee_base_type,
    engineer.id AS engineer_id,
    engineer.role_id AS engineer_role_id,
    analyst.id AS analyst_id,
    analyst.role_id AS analyst_role_id
FROM employee_base
LEFT OUTER JOIN engineer ON employee_base.id = engineer.id
LEFT OUTER JOIN analyst ON employee_base.id = analyst.id
JOIN role ON role.id = analyst.role_id 
WHERE lower(role.name) LIKE lower(?)

employee_role_join是一个AliasedClass同时公开Analyst和 的Engineer，然后我们可以使用它来创建一个 join-ON 子句，如下所示：

results = session.query(employee_role_join)\
        .join(Role, or_(  \
            employee_role_join.Engineer.role_id==Role.id,  \
            employee_role_join.Analyst.role_id==Role.id  \
        ))\
        .filter(Role.name.ilike('%petroleum%'))

这会将生成的 SQL 更改为JOIN role ON engineer.role_id = role.id OR analyst.role_id = role.id