Python server programming: using django-mptt for tree data structure processing

Python is an excellent programming language that is widely used in server-side programming. In server-side programming, processing tree data structures is a common requirement. At this time, you need to use some tools to help achieve it. Among them, django-mptt is a very convenient tool. This article will introduce how to use django-mptt for tree data structure processing.

1. What is django-mptt?

django-mptt is a tree structure processing application based on the Django framework. It can help us handle various operations such as creating, updating, deleting, and sorting tree structure data. It can greatly simplify our coding work and allow us to focus more on the processing of business logic.

2. Installation of django-mptt

Before using django-mptt, we need to install it. Enter the following command in the command line:

pip install django-mptt

3. Basic use of django-mptt

1. Create model

First, we need to create a model in models. Create a model in py, which is the parent class of the tree structure. The code is as follows:

from django.db import models
from mptt.models import MPTTModel, TreeForeignKey

class Category(MPTTModel):
    name = models.CharField(max_length=50, unique=True)
    parent = TreeForeignKey('self', on_delete=models.CASCADE, null=True, blank=True, related_name='children')

    class MPTTMeta:
        order_insertion_by = ['name']

    def __str__(self):
        return self.name

In this model, we use the two classes MPTTModel and TreeForeignKey. Among them, MPTTModel is the model base class provided by django-mptt for processing tree structures, and TreeForeignKey is the class provided by django-mptt for creating foreign keys. We define a name attribute and a parent attribute in the Category model. The parent attribute is of TreeForeignKey type, and its relationship with itself is a many-to-one relationship. In the MPTTMeta class, we specify the order_insertion_by attribute, which will play a role when we sort the tree structure.

2. Migrate

After we create the model, we need to perform a migration operation so that the model can create database tables in the server. Enter the following command in the command line:

python manage.py makemigrations
python manage.py migrate

3. Add data

After we create the Category model, we need to add some data so that we can really understand its usage. Enter the following command in the terminal:

python manage.py shell

After entering the Django shell, we can add some data as shown below:

>>> from blog.models import Category
>>> root = Category(name='root')
>>> root.save()
>>> child1 = Category(name='child1', parent=root)
>>> child1.save()
>>> child2 = Category(name='child2', parent=root)
>>> child2.save()
>>> child11 = Category(name='child11', parent=child1)
>>> child11.save()

In this code, we create a file named root root node and save it to the database. Then, we created two child nodes named child1 and child2, and established a parent-child relationship between them and the root node. Finally, we create a child node named child11 and establish a parent-child relationship with child1.

4. Query data

After we add the data, we can query our tree structure data through some APIs provided by django-mptt, as shown below:

>>> category_tree = Category.objects.all()
>>> category_tree
[<Category: root>, <Category: child1>, <Category: child11>, <Category: child2>]
>>> category_tree.get(name="root").get_family()
[<Category: root>, <Category: child1>, <Category: child11>, <Category: child2>]
>>> category_tree.get(name="root").get_children()
[<Category: child1>, <Category: child2>]
>>> category_tree.get(name="child1").get_children()
[<Category: child11>]
>>> category_tree.get(name="child11").get_parent()
<Category: child1>

In this code, we use Category.objects.all() to obtain the list of the entire data structure, and use the get_family() method to obtain the entire data structure. We also used the get_children() method to get the child nodes of a node, and the get_parent() method to get the parent node of a node.

5. Delete data

After we query the data, we can also delete it. When performing a deletion operation, we need to pay attention to deleting all child nodes of the node first, otherwise an exception will be thrown. The following is the code for the deletion operation:

>>> child1.delete()
>>> # 删除child1后，我们执行以下查询操作
>>> category_tree = Category.objects.all()
>>> category_tree
[<Category: root>, <Category: child2>]

In this example, we delete the child1 node and use the get_all() method to query the data structure. At this time, we can see that child1 and child11 have been deleted from the data structure.

4. Summary

Through this article, we have learned the basic usage of django-mptt, including creating models, migrating, adding data, querying data, and deleting data. Using django-mptt, we can easily handle the addition, deletion, modification and query operations of tree-structured data. I hope this article will be helpful to your study.

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