为什么 Flask WTForms 和 WTForms-SQLAlchemy QuerySelectField 会产生太多的值来解压? [英] Why does Flask WTForms and WTForms-SQLAlchemy QuerySelectField produce too many values to unpack?
问题描述
我有一个非常基本的 Flask 应用程序:
I've got a pretty basic Flask app:
from flask import Flask, render_template
from flask_wtf import FlaskForm
from wtforms_sqlalchemy.fields import QuerySelectField
from wtforms.validators import DataRequired
from flask_sqlalchemy import SQLAlchemy
from wtforms import StringField
db = SQLAlchemy()
app = Flask(__name__)
app.config['SQLALCHEMY_URI'] = 'sqlite:///:memory:'
app.config['SECRET_KEY'] = 'fnord'
db.init_app(app)
class Section(db.Model):
id = db.Column(db.Integer, primary_key = True)
name = db.Column(db.Text, nullable = False)
subject_id = db.Column(db.Integer, db.ForeignKey('subject.id'))
subject = db.relationship('Subject', back_populates='sections')
class Subject(db.Model):
id = db.Column(db.Integer, primary_key = True)
name = db.Column(db.Text, nullable = False)
sections = db.relationship('Section', back_populates='subject')
def do_something():
return Subject.query
class SelectionForm(FlaskForm):
name = StringField('Section Name', validators=[DataRequired()])
subject = QuerySelectField('Subject', query_factory=do_something, allow_blank=False, get_label='name')
with app.app_context():
db.create_all()
db.session.add(Subject(id=1, name='Science'))
db.session.add(Subject(id=2, name='Math'))
db.session.commit()
@app.route('/')
def main():
form = SelectionForm()
return render_template('index.html', form=SelectionForm())
app.run('0.0.0.0', port=5000, debug=True)
使用非常简单的模板:
<!DOCTYPE html>
<html>
<body>
{{ form.csrf_token }}
{{ form.name }}
{{ form.subject }}
</body>
</html>
问题在于我得到 ValueError: too many values to unpack (expected 2).这显然不是我所期望的 - 据我所知，我正在遵循我在网上看到的示例，但这里有些不同.问题是无论在 wtforms_sqlalchemy/fields.py 文件中发生了什么，它都会得到 (<class '__main__.Subject'>, (1), None)，而不是我所期望的可能是别的东西，因为它试图分配给 cls, key，可能是 (<class '__main__.Subject'>, 1).
The problem with this is that I get ValueError: too many values to unpack (expected 2). This is obviously not what I expected - as far as I can tell I'm following the examples that I've seen online, but something is different here. The problem is that whatever is going on under the hood in the wtforms_sqlalchemy/fields.py file, it's getting (<class '__main__.Subject'>, (1), None), instead of what I would have expected to probably be something else, since it's trying to assign to cls, key, probably (<class '__main__.Subject'>, 1).
那么我在这里做错了什么?
So what am I doing wrong here?
推荐答案
基于 pjcunningham 链接的补丁，由于 wtforms 尚未发布该更新，我继续创建了自己的monkeypatch:
Based on the patch that pjcunningham linked to, since wtforms hasn't released that update yet, I went ahead and created my own monkeypatch:
import wtforms_sqlalchemy.fields as f
def get_pk_from_identity(obj):
cls, key = f.identity_key(instance=obj)[:2]
return ':'.join(f.text_type(x) for x in key)
f.get_pk_from_identity = get_pk_from_identity
将它放入我的代码库中就足够了，直到他们发布了一个适用于最新版本的 SQLAlchemy 的版本.
Plopping that in my codebase is enough to work for now until they cut a release that works with the newest version of SQLAlchemy.
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