Flask-WTF进阶和WTForms扩展

Posted 2021-04-13 Python开发者

来源：孤独的自我

链接：https://segmentfault.com/a/1190000004502589

Flask-WTF和Flask-SQLAlchemy都是很好用的插件，然而当它们结合到一起后，就不是那么美妙了。

问题的提出

在models.py中定义了一个Article、Category和Tag类：

class Article(db.Model):

    """定义文章"""

 

    __tablename__ = 'articles'

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

    title = db.Column(db.String(128), unique=True, index=True)

    # 保存md格式的文本

    content = db.Column(db.Text)

    # 保存html格式的文本

    content_html = db.Column(db.Text)

    # 文章分类

    category_id = db.Column(db.Integer, db.ForeignKey('categories.id'))

    # 文章标签

    tags = db.relationship(

        'Tag', secondary='article_tag_ref', backref='articles')

class Category(db.Model):

    """文章分类"""

 

    __tablename__ = 'categories'

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

    name = db.Column(db.String(128), unique=True)

    articles = db.relationship('Article', backref='category', lazy='dynamic')

 

class Tag(db.Model):

    """文章标签"""

 

    __tablename__ = 'tags'

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

    name = db.Column(db.String(128), unique=True)

 

# 文章和标签的映射表 ，多对多关系

article_tag_ref = db.Table('article_tag_ref',

                           db.Column('article_id', db.Integer,

                                     db.ForeignKey('articles.id')),

                           db.Column('tag_id',  db.Integer,

                                     db.ForeignKey('tags.id'))

                           )

然后在forms.py中定义一个ArticleForm表单

class ArticleForm(Form):

 

    title = StringField(u"标题", validators=[Required()])

    category = QuerySelectField(u"分类", query_factory=getUserFactory(['id', 'name']), get_label='name')

    tags = StringField(u"标签", validators=[Required()])

    content = PageDownField(u"正文", validators=[Required()])

    submit = SubmitField(u"发布")

此时在处理表单的时候可以这样：

form = ArticleForm()

if form.validate_on_submit():

    article = Article(title=from.data.title, content=form.data.content,category=form.category.data)

    ...

等等，这样怎么处理form.data.tags？只有像下面这样写了：

"""

:param tags:

    标签列表，如[u'测试',u'Flask']

"""

def str_to_obj(tags):

    r = []

    for tag in tags:

        tag_obj = Tag.query.filter_by(name=tag).first()

        if tag_obj is None:

            tag_obj = Tag(name=tag)

        r.append(tag_obj)

    return r

然后在上面的代码中加入：

form = ArticleForm()

if form.validate_on_submit():

    article = Article(title=from.data.title, content=form.data.content, category=form.category.data, tags=str_to_obj(form.data.tags))

这样是不是很难看，像form.data.category就是一个对象，为撒到form.data.tags了就不是了，还要专门写一个函数来坐一个转换？这个时候就有必要扩展WTForms中的表单了。

WTForms入门

阅读WTForms文档，关于如何创建一个TagListField，贴一下代码：

class TagListField(Field):

    widget = TextInput()

 

    def _value(self):

        if self.data:

            return u', '.join(self.data)

        else:

            return u''

 

    def process_formdata(self, valuelist):

        if valuelist:

            self.data = [x.strip() for x in valuelist[0].split(',')]

        else:

            self.data = []

简单了看了一下WTForms源码，大致搞清楚了上面代码两个方法的作用：

1. _value The _value method is called by the TextInput widget to provide the value that is displayed in the form. 在初始化表单的时候，就是调用这个方法在表单中渲染数据

2. process_formdata 表单提交时，处理该字段的数据。

编写WTForm扩展

根据上面的代码，将TagListField中的字符串转为models.py中定义的Tag对象即可：

class TagListField(Field):

    widget = TextInput()

 

    def __init__(self, label=None, validators=None,

                 **kwargs):

        super(TagListField, self).__init__(label, validators, **kwargs)

 

    def _value(self):

        if self.data:

            r = u''

            for obj in self.data:

                r += self.obj_to_str(obj)

            return u''

        else:

            return u''

 

    def process_formdata(self, valuelist):

        print 'process_formdata..'

        print valuelist

        if valuelist:

            tags = self._remove_duplicates([x.strip() for x in valuelist[0].split(',')])

            self.data = [self.str_to_obj(tag) for tag in tags]

        else:

            self.data = None

 

    def pre_validate(self, form):

        pass

 

    @classmethod

    def _remove_duplicates(cls, seq):

        """去重"""

        d = {}

        for item in seq:

            if item.lower() not in d:

                d[item.lower()] = True

                yield item

 

    @classmethod

    def str_to_obj(cls, tag):

        """将字符串转换位obj对象"""

        tag_obj = Tag.query.filter_by(name=tag).first()

        if tag_obj is None:

            tag_obj = Tag(name=tag)

        return tag_obj

 

    @classmethod

    def obj_to_str(cls, obj):

        """将对象转换为字符串"""

        if obj:

            return obj.name

        else:

            return u''

主要就是在process_formdata这一步处理表单的数据，将字符串转换为需要的数据。最终就可以在forms.py中这样定义表单了：

...

class ArticleForm(Form):

    """编辑文章表单"""

 

    title = StringField(u'标题', validators=[Required()])

    category = QuerySelectField(u'分类', query_factory=get_category_factory(['id', 'name']), get_label='name')

    tags = TagListField(u'标签', validators=[Required()])

    content = PageDownField(u'正文', validators=[Required()])

    submit = SubmitField(u'发布')

...

在views.py中处理表单就很方便了：

def edit_article():

    """编辑文章"""

 

    form = ArticleForm()

    if form.validate_on_submit():

        article = Article(title=form.title.data, content=form.content.data)

        article.tags = form.tags.data

        article.category = form.category.data

        try:

            db.session.add(article)

            db.session.commit()

        except:

            db.session.rollback()

    return render_template('dashboard/edit.html', form=form)

代码是不是很简洁了？^_^。。。

当然了写一个完整的WTForms扩展还是很麻烦的。这里只是刚刚入门。可以看官方扩展QuerySelectField的源码。。。

最终效果

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