Django批量创建Model实例

1.前言：

将测试数据全部敲入数据库非常繁琐，而且如果与合作伙伴一起开发，部署，那么他们肯定也不想把时间花在一个一个录入数据的繁琐过程中，这时候，创建一个批量录入数据的脚本（population script)就非常有必要。

2.代码：

假设在models.py中定义的数据为下面：

from django.db import models

# Create your models here.
class Category(models.Model):
    name=models.CharField(max_length=128,unique=True)
    class Meta:
        verbose_name_plural="Categories"
    def __str__(self):
        return self.name 

class Page(models.Model):
    category=models.ForeignKey(Category,on_delete=models.CASCADE)
    title=models.CharField(max_length=128)
    url=models.URLField()
    views=models.IntegerField(default=0)
    def __str__(self):
        return self.title

　populate.py如下（仅供参考）：

import os
# In your live server environment, you’ll need to tell your WSGI application what settings
#  file to use. Do that with os.environ:
#reference source:https://docs.djangoproject.com/en/3.1/topics/settings/
os.environ.setdefault('DJANGO_SETTINGS_MODULE','tango_with_django_project.settings')

import django
django.setup()
from rango.models import Category,Page
#If you’re using components of Django “standalone” – for example, writing a Python script
# which loads some Django templates and renders them, or uses the ORM to fetch some data –
#  there’s one more step you’ll need in addition to configuring settings.
# After you’ve either set DJANGO_SETTINGS_MODULE or called configure(), you’ll need to call
# django.setup() to load your settings and populate Django’s application registry.
# reference source:https://docs.djangoproject.com/en/3.1/topics/settings/
def populate():
    python_pages=[
        {"title":"official",
        "url":"http://docs.python.org"},
        {"title":"How to think like a computer scientis",
        "url":"http://ww.greenteapress.com/thinkpy"},
        {"title":"learn python in 10 minites",
        "url":"http://www.korokithakis.net/tutorials/python"}
    ]

    django_pages=[
        {"title":"Official Django tutorial",
        "url":"https://docs.jangoproject.com/en/1.9/intro"},
        {"title":"Django Rocks",
        "url":"http://www.djangorocks.com"
        },
        {"title":"HOw to tango with django",
        "url":"http://www.tangowithdjango.com"}
    ]

    other_pages=[
        {"title":"Bottle",
        "url":"http://bottlepy.org"},
        {"title":"Flask",
        "url":"http://flask.pocoo.org"},
        {"title":"Bold test",
        "url":"http://boldtest.org"}
    ]
    cats={"Python":{"pages":python_pages},
    "Django":{"pages":django_pages},
    "Other Frameworks":{"pages":other_pages}}

    def add_page(cat,title,url,views=0):
        p=Page.objects.get_or_create(category=cat,title=title,url=url,views=views)[0]
        # p.url=url
        # p.views=views
        p.save()
        return p
    def add_cat(name):
        c=Category.objects.get_or_create(name=name)[0]
        c.save()
        return c
    for cat,cat_data in cats.items():
        c=add_cat(cat)
        for p in cat_data['pages']:
            add_page(c,p["title"],p['url'])
    for c in Category.objects.all():
        for p in Page.objects.filter(category=c):
            print("-{0}-{1}".format(str(c),str(p)))

if __name__=="__main__":
    print("starting rango population script")
    populate()

　3.代码要点

（1）在独立运行django的代码时，而不是通过 python manage.py runserver的方式运行时，必须使用django.setup()来引入Django项目的设置，而在引入设置之前还要指明 环境变量DJANGO_SETTINGS_MODULE用的是本项目的settings。

设置环境变量在python中常用os.environ，它返回一个字典类型，里面包含了所有环境变量的键值对，所以在这里使用字典的内置方法setdefault，将环境变量

'DJANGO_SETTINGS_MODULE' 设置为'tango_with_django_project.settings'（本项目的settings.py）。
参考：https://docs.djangoproject.com/en/3.1/topics/settings/#envvar-DJANGO_SETTINGS_MODULE

（2）get_or_create方法：（官方文档定义https://docs.djangoproject.com/en/3.1/ref/models/querysets/#get-or-create如下）

get_or_create(defaults=None, **kwargs)
A convenience method for looking up an object with the given kwargs (may be empty if your model has defaults for all fields),
 creating one if necessary.
Returns a tuple of (object, created), where object is the retrieved or created object and created is a boolean specifying whether a new 
object was created.
This is meant to prevent duplicate objects from being created when requests are made in parallel, and as a shortcut to boilerplatish code. 

　在这里，需要注意的是，如果在创建model instance时，仅在model有默认值的情况下可以不输入任何kwargs，否则必须至少输入一个值（field,如这里page的category，或者Category的name)，然后该方法会带着这个值先去找有没有该值下的model instance，如果没有则创建一个新的，返回（object,created)，这里object 是新创建的对象的reference，created为True.

4.运行查看

运行python populate.py：

然后登陆admin页面查看：

可以看到，数据全部被读入数据库。