(Updated April 7, 2021) Django framework model properties in detail

1 definition

Define a model class in the models.py file as shown in the following example:

from django.db import models

# Create your models here.
Prepare the model class for the book list information
class BookInfo(models.Model) :
    # create field, field type...
    name = models.CharField(max_length=20, verbose_name='name')
    pub_date = models.DateField(verbose_name='Release Date',null=True)
    readcount = models.IntegerField(default=0, verbose_name='Reading volume')
    commentcount = models.IntegerField(default=0, verbose_name='Comment volume')
    is_delete = models.BooleanField(default=False, verbose_name='Logical delete')

    class Meta:
        db_table = 'bookinfo'  SQL > alter table name
        verbose_name = 'book'  # The name to display on the admin site

    def __str__(self) :
        Define the display information for each data object
        return self.name

Prepare the model class for the character list information
class PeopleInfo(models.Model) :
    GENDER_CHOICES = (
        (0.'male'),
        (1.'female')
    )
    name = models.CharField(max_length=20, verbose_name='name')
    gender = models.SmallIntegerField(choices=GENDER_CHOICES, default=0, verbose_name='gender')
    description = models.CharField(max_length=200, null=True, verbose_name='Description')
    book = models.ForeignKey(BookInfo, on_delete=models.CASCADE, verbose_name='book')  Outside the # key
    is_delete = models.BooleanField(default=False, verbose_name='Logical delete')

    class Meta:
        db_table = 'peopleinfo'
        verbose_name = 'People information'

    def __str__(self) :
        return self.name
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1) Database table name

If the table name is not specified, Django defaults to lowercase app name _ Lowercase model class name database table name.

You can specify the database table name using db_table.

2) About primary keys

Django creates auto-growing primary key columns for tables. There is only one primary key column per model, and django does not create auto-growing primary key columns if you use the option to set a primary key column for a property.

The default primary key column attribute is ID. Pk can be used instead. Pk is the primary key.

3) Attribute naming restrictions

• Cannot be a Python reserved key.
• The use of consecutive underscores is disallowed because of the way Django queries are run.
• When defining attributes, you need to specify the field type. The syntax is as follows:

Property = Models. Field type (option)Copy the code

4) Field type

5) options

Null is the database category concept, blank is the form validation category

6) foreign keys

When setting a foreign key, use the on_delete option to specify what to do with the foreign key reference table data when the primary table deletes data. Django.db. models contains optional constants:

• CASCADE Indicates that data in the primary table can be deleted
• PROTECT prevents the deletion of data applied by foreign keys from the primary table by raising ProtectedError
• SET_NULL is set to NULL, available only if the field NULL =True allows NULL
• SET_DEFAULT is set to the default value and is available only if the field has a default value
• SET() sets a particular value or calls a particular method
• DO_NOTHING does nothing, and this option raises an IntegrityError if cascade is specified in front of the database

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