WTForms-Alchemy ModelForm不会使用现有对象

Question

这是我在简单的Flask WTForms示例中的代码。我一直在努力学习如何让ModelForms进行验证。验证与标准表单一起使用没问题。对我所做错的任何帮助都表示赞赏。

from flask.ext.wtf import Form
from wtforms_alchemy import model_form_factory

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

id = db.Column(db.Integer, primary_key=True)
email = db.Column(db.String(128), nullable=False, unique=True)
username = db.Column(db.String(32), nullable=False, unique=True)

BaseModelForm = model_form_factory(Form)

class ModelForm(BaseModelForm):
    @classmethod
    def get_session(cls):
        return db.session

class UserForm(ModelForm):
    class Meta:
       model = User


flask_shell >> uf = UserForm(obj=jeff, csrf_enabled=False)
flask_shell >> uf.validate()  #False
flask_shell >> uf.errors

{'email': ['This field is required.'],
 'password_hash': ['This field is required.'],
 'username': ['This field is required.']}


flask_shell >> uf.__dict__

{'SECRET_KEY': '',
 '_errors': None,
 '_fields': OrderedDict([('csrf_token',
            <wtforms.ext.csrf.fields.CSRFTokenField at 0x1075239e8>),
          ('email',
           <wtforms_components.fields.html5.StringField at 0x107523ac8>),
          ('username',
           <wtforms_components.fields.html5.StringField at 0x107523b70>),
 '_obj': <User 'jeff'>,
 '_prefix': '',
 'csrf_enabled': False,
 'csrf_token': <wtforms.ext.csrf.fields.CSRFTokenField at 0x1075239e8>,
 'email': <wtforms_components.fields.html5.StringField at 0x107523ac8>,
 'meta': <wtforms.form.Meta at 0x107523898>,
 'username': <wtforms_components.fields.html5.StringField at 0x107523b70>}