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Django ORM is a classic ORM framework in Python. It is part of the Django Web framework and provides a convenient way for database operations. ORM stands for Object Relational Mapping, which can map tables in relational databases to classes in Python, thereby simplifying the development process and improving development efficiency. This article will introduce Django ORM in detail.
I. The basic concept of ORM
ORM is a technology that maps objects to relational databases. It mainly implements the following three functions:
The main advantage of ORM is that it can reduce the time and workload of developers writing repeated SQL statements, and it can reduce errors caused by adjustments and changes to SQL statements.
II. Advantages of Django ORM
Compared with other ORM frameworks, Django ORM has the following advantages:
III. How to use Django ORM
First you need to install Django, you can use pip to install:
pip install Django
When using Django ORM, you need to define the model class first. The model class is a class in Python that defines the fields in the data table and other parts of the data table. Metadata, such as table names, indexes, etc. The following is a simple model class definition:
from django.db import models class Book(models.Model): title = models.CharField(max_length=100) author = models.CharField(max_length=50) pub_date = models.DateTimeField()
In the above code, we use the models
module provided by Django ORM to define a class named Book
Data table, which contains three fields: title
, author
, pub_date
. max_length
is used to specify the maximum length of string type fields, DateTimeField
is used to store time type fields.
After completing the definition of the model class, you need to generate the database table through migration. Django ORM provides an automatic migration function. You only need to run the following command to generate a data table:
python manage.py makemigrations python manage.py migrate
The above command creates the Book
table, and the table structure corresponds to the defined model class.
a. Create records
You can easily add new records to the data table through the model class. In the following code, We create a new record and save it to the database:
from datetime import datetime book = Book(title='Django ORM Tutorial', author='Terry', pub_date=datetime.now()) book.save()
b. Updating the record
Updating a record using Django ORM is very simple, just query the record first and then update it and save it. The following is a simple update code example:
book = Book.objects.get(id=1) book.title = 'Updated Title' book.save()
c. Delete records
Deleting records is also very simple, just execute the following code:
book = Book.objects.get(id=1) book.delete()
d. Query Record
In Django ORM, you can use objects
objects to query. The following is a simple query example code:
books = Book.objects.all() for book in books: print(book.title, book.author, book.pub_date)
This code will output Book
The title
, author
, and pub_date
fields for all records in the table.
IV. Advanced query operations
In addition to basic CRUD operations, Django ORM also supports some advanced query operations, such as join table query, query condition combination, aggregation operation, etc. The following are some examples code.
a. Join table query
Django ORM supports two methods of join table query: one is to associate through the ForeignKey
field, and the other is to associate through the self- Define queries to perform correlations.
# 通过ForeignKey字段关联 class Author(models.Model): name = models.CharField(max_length=50) class Book(models.Model): title = models.CharField(max_length=100) author = models.ForeignKey(Author, on_delete=models.CASCADE) books = Book.objects.filter(author__name='Leo Tolstoy') # 以上代码查询了作者名为'Leo Tolstoy'的所有图书 # 通过自定义查询进行关联 books = Book.objects.raw('SELECT * FROM app_book INNER JOIN app_author ON app_book.author_id = app_author.id WHERE app_author.name = %s', ['Leo Tolstoy'])
b. Query condition combination
In Django ORM, you can use the Q
object to combine multiple query conditions to achieve more complex queries. The following is a sample code:
from django.db.models import Q books = Book.objects.filter(Q(title__contains='Django') | Q(author__contains='Guido')) # 以上代码查询了标题中包含'Django'或作者名中包含'Guido'的所有图书
c. Aggregation operation
Aggregation operation is used to group data or summarize statistics. Aggregation operations supported in Django ORM include: Avg
, Max
, Min
, Count
, Sum
, etc. The following is a sample code:
from django.db.models import Avg avg_pub_date = Book.objects.all().aggregate(Avg('pub_date')) # 以上代码计算了所有图书的发布时间的平均值
V. Summary
This article provides a detailed introduction to the ORM framework Django ORM in Python. Django ORM is an easy-to-use, feature-rich, and scalable ORM framework that can help developers achieve rapid development and more efficient database operations. In addition to basic CRUD operations, Django ORM also supports some advanced query operations, such as join table queries, query condition combinations, aggregation operations, etc., which can meet the needs of more data operations.
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