ORM framework in Python Django ORM practice

With the development of the Internet, development software has become more and more popular. In order to improve development efficiency and code management, many languages ​​​​provide ORM frameworks, and Python is no exception. Django is a Python web framework that provides a powerful ORM framework - Django ORM. This article will introduce how to use Django ORM to manage databases.

1. Installing Django

Before using Django ORM, you need to install Django. You can use pip to install it, the command is as follows:

pip install django

2. New Django project

After installing Django, you can use it to create a new project, the command is as follows:

django-admin startproject project_name

This will create a Django project named project_name.

3. Create database model

In Django ORM, the database model can be defined as a Python class. In the project's app directory, create a file named models.py and define the model in it. For example, to create a model named Book with title, author, pub_date and price attributes, it can be defined as follows:

from django.db import models
   
class Book(models.Model):
    title = models.CharField(max_length=100)
    author = models.CharField(max_length=200)
    pub_date = models.DateField()
    price = models.DecimalField(max_digits=5, decimal_places=2)

Here, Book inherits the Model class in Django ORM and defines four Attributes. CharField represents character type, DateField represents date type, and DecimalField represents decimal type. When defining each property, you can use parameters to control their type, length, precision, etc.

In addition, you can also define methods and class methods for models. For example, define a class method named get_books in the Book model to obtain all books from the database, as follows:

class Book(models.Model):
    # 类属性
    title = models.CharField(max_length=100)
    author = models.CharField(max_length=200)
    pub_date = models.DateField()
    price = models.DecimalField(max_digits=5, decimal_places=2)

    # 类方法
    @classmethod
    def get_books(cls):
        return cls.objects.all()

Here, use the classmethod modifier to modify the get_books method, and Defined as a class method. This method uses the objects attribute in Django ORM to get all Book objects.

4. Run database migration

After defining the model, you need to create tables in the database. This process can be accomplished using the makemigrations and migrate commands provided by Django ORM. Using the makemigrations command will generate a migration file containing changes to the model. Using the migrate command will execute the migration file and apply the changes to the database. The command is as follows:

python manage.py makemigrations
python manage.py migrate

5. Use Django ORM to manage the database

After defining the database model and completing the database migration, you can use Django ORM to manage the database. For example, in views.py you can write the following code:

from django.shortcuts import render
from .models import Book

def book_list(request):
    books = Book.get_books()
    return render(request, 'book_list.html', {'books': books})

Here, import the Book model from models.py and use the get_books method to get all the books. They are then passed as parameters into the render function, which will use the template file book_list.html to render the page.

In book_list.html, you can use the following code to display a list of books:

{% for book in books %}
    <div class="book">
        <h2>{{ book.title }}</h2>
        <p>{{ book.author }} - {{ book.pub_date|date:"Y年m月d日" }}</p>
        <p>价格：{{ book.price }}</p>
    </div>
{% endfor %}

Here, use a for loop to traverse all books and output their attributes. It should be noted that when outputting the pub_date attribute, a date filter is used to format the date into the form of year, month and day.

6. Summary

Django ORM is a powerful ORM framework that can help developers manage databases easily. This article introduces the process of using Django ORM to create models, run database migrations, and manage databases. I hope this article can help beginners better understand the application of Django ORM.

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