查询一对多关系 SQLAlchemy

Question

I am trying to query the users based upon their skills from these tables.

class User(UserMixin, db.Model):
    __tablename__ = 'users'

    id = db.Column(db.Integer, primary_key=True)
    email = db.Column(db.String(64), unique=True, index=True)
    username = db.Column(db.String(64), unique=True, index=True)
    skills = db.relationship('Skill', backref='author', lazy='dynamic')

---

class Skill(db.Model):
    __tablename__ = 'skills'

    id = db.Column(db.Integer, primary_key=True)
    skill = db.Column(db.String(64), index=True)
    author_id = db.Column(db.Integer, db.ForeignKey('users.id'))

i tried this in User table and got this error.

@classmethod
def users_by_skill(cls, skill):
    return User.query.join(Skill).filter(skill.skill).all()

---

AttributeError: 'str' object has no attribute 'skill'

Where i am missing badly?

Answer 1

You define the following class method:

@classmethod
def users_by_skill(cls, skill):
    return User.query.join(Skill).filter(skill.skill).all()

You are probably expecting to use this function like so:

users = Users.users_by_skill('nunchuk')

That means the skill argument in users_by_skill is a string. Then, you try to use skill.skill , which essentially is like doing 'nunchuk'.skill . Python does not have a skill attribute on the string class, hence the error.

The filter function actually takes a Criteria object. In other words, you don't pass it a value like "filter" , you instead pass it a criterion that represents the notion of "the skill column on the Skill table must equal 'nunchuk'". You can do this using syntax like the following:

@classmethod
def users_by_skill(cls, skill_name):
    return User.query.join(Skill).filter(Skill.skill == skill_name).all()