如何将Pandas Dataframe写入现有的Django模型

问题描述

我试图将Pandas DataFrame中的数据插入使用SQLite后端的现有Django模型 Agency 中.但是，按照的答案进行操作将Pandas Dataframe转换为Django模型和将Pandas DataFrame保存到Django Model 导致整个SQLite表被替换并破坏了Django代码.具体来说，是由Django自动生成的 id 主键列替换为 index ，这会导致在渲染模板时出现错误().

I am trying to insert data in a Pandas DataFrame into an existing Django model, Agency, that uses a SQLite backend. However, following the answers on How to write a Pandas Dataframe to Django model and Saving a Pandas DataFrame to a Django Model leads to the whole SQLite table being replaced and breaking the Django code. Specifically, it is the Django auto-generated id primary key column that is replaced by index that causes the errors when rendering templates (no such column: agency.id).

这是在SQLite表 agency 上使用Pandas to_sql的代码和结果.

Here is the code and the result of using Pandas to_sql on the SQLite table, agency.

在 models.py 中:

class Agency(models.Model):
    name = models.CharField(max_length=128)

在 myapp/management/commands/populate.py 中:

class Command(BaseCommand):

def handle(self, *args, **options):

    # Open ModelConnection
    from django.conf import settings
    database_name = settings.DATABASES['default']['NAME']
    database_url = 'sqlite:///{}'.format(database_name)
    engine = create_engine(database_url, echo=False)

    # Insert data data
    agencies = pd.DataFrame({"name": ["Agency 1", "Agency 2", "Agency 3"]})
    agencies.to_sql("agency", con=engine, if_exists="replace")

调用" python manage.py populate "成功将三个代理添加到表中:

Calling 'python manage.py populate' successfully adds the three agencies into the table:

index    name
0        Agency 1
1        Agency 2
2        Agency 3

但是，这样做已更改了表的DDL:

However, doing so has changed the DDL of the table from:

CREATE TABLE "agency" ("id" integer NOT NULL PRIMARY KEY AUTOINCREMENT, "name" varchar(128) NOT NULL)

收件人:

CREATE TABLE agency (
  "index" BIGINT,
  name TEXT
);
CREATE INDEX ix_agency_index ON agency ("index")

如何将DataFrame添加到Django管理的模型中并保持Django ORM完整?

How can I add the DataFrame to the model managed by Django and keep the Django ORM intact?

推荐答案

要回答我自己的问题，当我如今经常使用Pandas将数据导入Django时，我犯的错误是试图使用Pandas内置的Sql Alchemy正在修改基础数据库表定义的数据库ORM.在上面的上下文中，您可以简单地使用Django ORM连接并插入数据:

To answer my own question, as I import data using Pandas into Django quite often nowadays, the mistake I was making was trying to use Pandas built-in Sql Alchemy DB ORM which was modifying the underlying database table definition. In the context above, you can simply use the Django ORM to connect and insert the data:

from myapp.models import Agency

class Command(BaseCommand):

    def handle(self, *args, **options):

        # Process data with Pandas
        agencies = pd.DataFrame({"name": ["Agency 1", "Agency 2", "Agency 3"]})

        # iterate over DataFrame and create your objects
        for agency in agencies.itertuples():
            agency = Agency.objects.create(name=agency.name)

但是，您可能经常想使用外部脚本而不是上面的管理命令或Django的shell导入数据.在这种情况下，您必须首先通过调用 setup 方法来连接到Django ORM:

However, you may often want to import data using an external script rather than using a management command, as above, or using Django's shell. In this case you must first connect to the Django ORM by calling the setup method:

import os, sys

import django
import pandas as pd

sys.path.append('../..') # add path to project root dir
os.environ["DJANGO_SETTINGS_MODULE"] = "myproject.settings"

# for more sophisticated setups, if you need to change connection settings (e.g. when using django-environ):
#os.environ["DATABASE_URL"] = "postgres://myuser:mypassword@localhost:54324/mydb"

# Connect to Django ORM
django.setup()

# process data
from myapp.models import Agency
Agency.objects.create(name='MyAgency')

• 在这里，我已将设置模块 myproject.settings 导出到 DJANGO_SETTINGS_MODULE ，以便可以使用 django.setup()项目设置.

  • Here I have exported my settings module myproject.settings to the DJANGO_SETTINGS_MODULE so that django.setup() can pick up the project settings.

    取决于运行脚本的位置，您可能需要转到系统路径，以便Django可以找到设置模块.在这种情况下，我在项目根目录下的两个目录中运行脚本.

    Depending on where you run the script from, you may need to path to the system path so Django can find the settings module. In this case, I run my script two directories below my project root.

    您可以在调用 setup 之前修改任何设置.如果您的脚本连接到数据库的方式与 settings 中配置的方式不同.例如，当针对Django/postgres Docker容器在本地运行脚本时.

    You can modify any settings before calling setup. If your script needs to connect to the DB differently than whats configured in settings. For example, when running a script locally against Django/postgres Docker containers.

    请注意，上面的示例使用的是 django-environ 指定数据库设置.

    Note, the above example was using the django-environ to specify DB settings.

    这篇关于如何将Pandas Dataframe写入现有的Django模型的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！