Django错误：ValueError：无法分配“（<Category：Cultural>，True）”：“Site.category”必须是“Category”实例

Question

我需要创建一个从 csv 文件导入数据的数据库。按照练习的说明，我为脚本创建了模型和文件，但是当我运行命令 python manage.py runscript many_load 时，它给了我标题中的错误。 代码如下：

-models.py：

from django.db import models


class Category(models.Model):
    category = models.CharField(max_length=128)

    def __str__(self):
        return self.category

class State(models.Model):
    state = models.CharField(max_length=25)

    def __str__(self):
        return self.state


class Region(models.Model):
    region = models.CharField(max_length=25)

    def __str__(self):
        return self.region

class Iso(models.Model):
    iso = models.CharField(max_length=5)

    def __str__(self):
        return self.iso

class Site(models.Model):
    name = models.CharField(max_length=128)
    year = models.CharField(max_length=128)
    area = models.CharField(max_length=128)
    describe = models.TextField(max_length=500)
    justify = models.TextField(max_length=500, null=True)
    longitude = models.TextField(max_length=25, null=True)
    latitude = models.TextField(max_length=25, null=True)

    #one to many field
    category = models.ForeignKey(Category, on_delete=models.CASCADE)
    state = models.ForeignKey(State, on_delete=models.CASCADE)
    region = models.ForeignKey(Region, on_delete=models.CASCADE)
    iso = models.ForeignKey(Iso, on_delete=models.CASCADE)

    def __str__(self):
        return self.name

- many_load.py：

import csv

from unesco.models import Site, Category, Iso, Region, State


def run():
    fhand = open('unesco/whc-sites-2018-clean.csv')
    reader = csv.reader(fhand)
    next(reader)

    Category.objects.all().delete()
    Iso.objects.all().delete()
    Region.objects.all().delete()
    State.objects.all().delete()

    Site.objects.all().delete()

    for row in reader:
        # print(row)
        # print (len(row))

        name = row[0]
        describe = row[1]
        justification = row[2]
        year = row[3]
        longitude = row[4]
        latitude = row[5]
        area = row[6]

        category = Category.objects.get_or_create(category=row[7])
        state = State.objects.get_or_create(state=row[8])
        region = Region.objects.get_or_create(region=row[9])
        iso = Iso.objects.get_or_create(iso=row[10])

        st = Site(category=category, state=state, region=region, iso=iso,
                  name=name, area=area, describe=describe, year=year, justification=justification,
                  longitude=longitude, latitude=latitude)
        st.save()

我必须承认我对导入的整个过程不是很了解，所以我无法弄清楚如何看..如果您能向我解释一下，将不胜感激。提前致谢！

Answer 1

get_or_create 方法返回两个元素的元组：

返回 (object, created) 的元组，其中 object 是检索或创建的对象， created 是指定是否创建新对象的布尔值。

所以，你需要unpack tuples来提取模型

category, _ = Category.objects.get_or_create(category=row[7])
state, _ = State.objects.get_or_create(state=row[8])
region, _ = Region.objects.get_or_create(region=row[9])
iso, _ = Iso.objects.get_or_create(iso=row[10])

st = Site(category=category, state=state, region=region, iso=iso,
                  name=name, area=area, describe=describe, year=year, justification=justification,
                  longitude=longitude, latitude=latitude)

Python 中的单下划线_ 变量通常用作“一次性”变量名，如here 所述