Flask-WTF进阶和WTForms扩展

孤独的自我

Flask-WTFFlask-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

models.py中定义了一个ArticleCategoryTag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')
...

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

clipboard.png

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