如何查询多个多态继承表上的关系?

时间:2018-07-12 15:32:32

标签: sqlalchemy flask-sqlalchemy

假设您有以下简化的示例架构,该架构使用SQLAlchemy联接表多态继承。 EngineerAnalyst模型具有Role关系。 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 Role的{​​{1}}名称中有“石油”的地方,我该怎么做?

我尝试了很多方法。我最接近的是这个,它只会返回name个匹配项:

Analyst

如果我尝试执行类似的操作,则会得到employee_role_join = with_polymorphic(EmployeeBase, [Engineer, Analyst]) results = db.session.query(employee_role_join).join(Role).filter(Role.name.ilike('%petroleum%')) ,因为我正在搜索联接的AttributeError表的属性:

Role

2 个答案:

答案 0 :(得分:3)

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analyst.role_id列上连接:

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_joinAliasedClass,它同时公开AnalystEngineer,然后我们可以使用它们来创建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%'))

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

答案 1 :(得分:2)

role_id上定义EmployeeBase。即使Intern没有回到role表的关系,在这种情况下该字段也可以为null。

我将EmployeeBase更改为此:

class EmployeeBase(db.Model):

    __tablename__ = 'employee_base'

    id = db.Column(db.Integer, primary_key=True)
    role_id = db.Column(db.Integer, db.ForeignKey('role.id'), index=True)

    given_name = db.Column(db.String(16))
    surname = db.Column(db.String(16))

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

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

并从所有其他员工模型中删除了role_id列定义。

db.create_all()

petrolium_engineer = Role(name='Petrolium Engineer')
geotech_engineer = Role(name='Geotech Engineer')
analyst_petrolium = Role(name='Analyst of Petrolium')

db.session.add(petrolium_engineer)
db.session.add(geotech_engineer)
db.session.add(analyst_petrolium)

db.session.add(
    Intern(given_name='Joe', surname='Blogs', term_ends=datetime.now())
)
db.session.add(
    Engineer(given_name='Mark', surname='Fume', role=petrolium_engineer)
)
db.session.add(
    Engineer(given_name='Steve', surname='Rocks', role=geotech_engineer)
)
db.session.add(
    Analyst(given_name='Cindy', surname='Booker', role=analyst_petrolium)
)

db.session.commit()

petrolium_roles = db.session.query(EmployeeBase).join(Role).\
                    filter(Role.name.contains('Petrolium')).all()

for emp in petrolium_roles:
    print(f'{emp.given_name} {emp.surname} is {emp.role.name}')

# Mark Fume is Petrolium Engineer
# Cindy Booker is Analyst of Petrolium