第12章：关注-Flask Web 开发(第2版)

# 使用 Flask-SQLAlchemy 定义多对多关联关系

# 关联表
registrations = db.Table('registrations',
    db.Column('student_id', db.Integer, db.ForeignKey('students.id')),
    db.Column('class_id', db.Integer, db.ForeignKey('classes.id'))
)

# 学生
class Student(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String)
    classes = db.relationship('Class',
                              secondary=registrations,
                              backref=db.backref('students', lazy='dynamic'),
                              lazy='dynamic')

# 课程
class Class(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String)

>>> s.classes.append(c)
>>> db.session.add(s)

>>> s.classes.all()
>>> c.students.all()

>>> s.classes.remove(c)

# 示例 12-1. app/models.py: 使用模型类定义“关注”关联表
class Follow(db.Model):
    __tablename__ = 'follows'
    follower_id = db.Column(db.Integer, db.ForeignKey('users.id'),
                            primary_key=True)
    followed_id = db.Column(db.Integer, db.ForeignKey('users.id'),
                            primary_key=True)
    timestamp = db.Column(db.DateTime, default=datetime.utcnow)

# 示例 12-2. app/models.py: 使用两个一对多关系实现一个多对多关系
class User(UserMixin, db.Model):
    # ...
    followed = db.relationship('Follow',
                               foreign_keys=[Follow.follower_id],
                               backref=db.backref('follower', lazy='joined'),
                               lazy='dynamic',
                               cascade='all, delete-orphan')
    followers = db.relationship('Follow',
                                foreign_keys=[Follow.followed_id],
                                backref=db.backref('followed', lazy='joined'),
                                lazy='dynamic',
                                cascade='all, delete-orphan')

# 示例 12-3. app/models.py: 关注功能的辅助方法
class User(db.Model):
    # ...
    def follow(self, user):
        if not self.is_following(user):
            f = Follow(follower=self, followed=user)
            db.session.add(f)

    def unfollow(self, user):
        f = self.followed.filter_by(followed_id=user.id).first()
        if f:
            db.session.delete(f)

    def is_following(self, user):
        if user.id is None:
            return False
        return self.followed.filter_by(
            followed_id=user.id).first() is not None

    def is_followed_by(self, user):
        if user.id is None:
            return False
        return self.followers.filter_by(
            follower_id=user.id).first() is not None

<!-- 示例 12-4. app/templates/user.html: 使用关注功能增加用户资料页面-->
{% if current_user.can(Permission.FOLLOW) and user != current_user %}
    {% if not current_user.is_following(user) %}
    <a href="{{ url_for('.follow', username=user.username) }}"
        class="btn btn-primary">关注</a>
    {% else %}
    <a href="{{ url_for('.unfollow', username=user.username) }}"
        class="btn btn-default">取消关注</a>
    {% endif %}
{% endif %}
<a href="{{ url_for('.followers', username=user.username) }}">
    已关注: <span class="badge">{{ user.followers.count() }}</span>
</a>
<a href="{{ url_for('.followed_by', username=user.username) }}">
    被关注: <span class="badge">{{ user.followed.count() }}</span>
</a>
{% if current_user.is_authenticated and user != current_user and
    user.is_following(current_user) %}
| <span class="label label-default">关注了你</span>
{% endif %}

# 示例 12-5. app/main/views.py: “关注”的路由和视图函数
@main.route('/follow/<username>')
@login_required
@permission_required(Permission.FOLLOW)
def follow(username):
    user = User.query.filter_by(username=username).first()
    if user is None:
        flash('非法用户.')
        return redirect(url_for('.index'))
    if current_user.is_following(user):
        flash('你已经关注过该用户了.')
        return redirect(url_for('.user', username=username))
    current_user.follow(user)
    db.session.commit()
    flash('你已成功关注 %s.' % username)
    return redirect(url_for('.user', username=username))

# 示例 12-6. app/main/views.py: “已关注”路由和视图函数
@main.route('/followers/<username>')
def followers(username):
    user = User.query.filter_by(username=username).first()
    if user is None:
        flash('非法用户.')
        return redirect(url_for('.index'))
    page = request.args.get('page', 1, type=int)
    pagination = user.followers.paginate(
        page, per_page=current_app.config['FLASKY_FOLLOWERS_PER_PAGE'],
        error_out=False)
    follows = [{'user': item.follower, 'timestamp': item.timestamp}
               for item in pagination.items]
    return render_template('followers.html', user=user, title="已关注",
                           endpoint='.followers', pagination=pagination,
                           follows=follows)

SELECT p.id AS id, p.author_id, p.body, f.follower_id, f.followed_id
FROM posts AS p
INNER JOIN follows AS f
ON p.author_id = f.followed_id
WHERE f.follower_id = 2

return db.session.query(Post).select_from(Follow).\
    filter_by(follower_id=self.id).\
    join(Post, Follow.followed_id == Post.author_id)

return Post.query.join(Follow, Follow.followed_id == Post.author_id)\
    .filter(Follow.follower_id == self.id)

# 示例 12-7. app/models.py: 获取被关注者发表的博文
class User(db.Model):
    # ...
    @property
    def followed_posts(self):
        return Post.query.join(Follow, Follow.followed_id == Post.author_id)\
            .filter(Follow.follower_id == self.id)

# 示例 12-8. app/main/views.py: 显示所有博文或只显示被关注者的博文
@main.route('/', methods = ['GET', 'POST'])
def index():
    # ...
    show_followed = False
    if current_user.is_authenticated:
        show_followed = bool(request.cookies.get('show_followed', ''))
    if show_followed:
        query = current_user.followed_posts
    else:
        query = Post.query
    pagination = query.order_by(Post.timestamp.desc()).paginate(
        page, per_page=current_app.config['FLASKY_POSTS_PER_PAGE'],
        error_out=False)
    posts = pagination.items
    return render_template('index.html', form=form, posts=posts,
                           show_followed=show_followed, pagination=pagination)

# 示例 12-9. app/main/views.py: 所有博文或已关注用户博文的选择
@main.route('/all')
@login_required
def show_all():
    resp = make_response(redirect(url_for('.index')))
    resp.set_cookie('show_followed', '', max_age=30*24*60*60)  # 30 days
    return resp

@main.route('/followed')
@login_required
def show_followed():
    resp = make_response(redirect(url_for('.index')))
    resp.set_cookie('show_followed', '1', max_age=30*24*60*60)  # 30 days
    return resp

# 示例 12-10. app/models.py: 在创建用户的时候，将自己设为自己的关注者
class User(UserMixin, db.Model):
    # ...
    def __init__(self, **kwargs):
        # ...
        self.follow(self)

# 示例 12-11. app/models.py: 将用户设置为自己的关注者
class User(UserMixin, db.Model):
    # ...
    @staticmethod
    def add_self_follows():
        for user in User.query.all():
            if not user.is_following(user):
                user.follow(user)
                db.session.add(user)
                db.session.commit()
    # ...

(venv) $ flask shell
>>> User.add_self_follows()