从一个来源写入两个链接的flask-sqlalchemy模型

Question

I'm a beginner in flask, building a flask-based webapplication. I'm using flask-sqlalchemy to connect to my sqlite db.

When I import data from the form and write it to the database, the 'apple_id' column in the 'Pear' model contains NULL for every entry. It's supposed to hold the ID of the 'Apple'-entry. Other data is written as I expected. The two table have a one-to-many relationship, one apple can be referenced by multiple pears.

I simplified the script to make it easier to analyse.

in models.py:

from flask import current_app, request, url_for
from . import db

class Apple(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(64))

class Pear(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    apple_id = db.Column(db.Integer, db.ForeignKey('cabinet.id'))
    amount = db.Column(db.Integer)

In views.py

from . import edit
from flask import render_template, url_for, redirect, flash
from .forms import ApplePearForm
from ..models import Apple, Pear
from .. import db

@edit.route('/apples-and-pears', methods=['GET', 'POST'])
def apples_and_pears():
    form = ApplePearForm()
    if form.validate_on_submit():
        apple = Apple(name=form.name.data)
        db.session.add(apple)
        pear = Pear(apple_id=apple.id, amount=4)
        db.session.add(pear)
        flash('fruit was added to database')
        return redirect(url_for('browse.fruit_list'))
    return render_template('edit/apples_and_pears.html', form=form)

Answer 1

If you need a relationship between tables you should use relationship to define. backref add reference on both side so you can do this pear=Pear(apple=apple) :

class Apple(db.Model): 
    ...
    pears = db.relationship('Pear', backref='apple') 

class Pear(db.Model): 
    ...
    apple_id = db.Column(db.Integer, db.ForeignKey('cabinet.id')

#view 
apple = Apple(...)
pear = Pear(apple=apple, ...)