09 Django ORM common fields and parameters

I. Description

• Name of the table is automatically generated, if you want to customize the table name, you need to specify Meta class model in db_table parameters, it is strongly recommended to use lowercase table names, especially when using MySQL as the backend database.
• id field is added automatically, if you want to specify a custom primary key, just specify primary_key = True can be in one field. But the need to use autofield (primary_key = True) If Django find that you have explicitly set Field.primary_key, it will not automatically add the ID column.
• In this example using PostgreSQL CREATE TABLE SQL syntax formats, but it is worth noting that, Django will be generated according to the corresponding SQL statement specified in the profile of the type of backend database.
• Django supports MySQL5.5 and later.

Two, ORM common fields and parameters

1.AutoField

int auto increment, must fill in the parameters primary_key = True. When the model, if there is no auto-increment, then automatically creates a column called id columns.

2.IntegerField

An integral type, in the range -2147483648 to 2147483647. (Generally do it to save the phone number (the number of bits is not enough), direct deposit with string,)

3.CharField

Character type, must provide max_length parameters, characters indicating max_length.

We should know that the MySQL database in Django CharField corresponding to the varchar type, do not set the corresponding field of type char, but Django allows us to customize the new field, following me to customize the database corresponding to the type of char

Custom fields may be frequently used in the actual project applications, where the need for him to leave impression

from django.db import models

# Create your models here.
#Django中没有对应的char类型字段，但是我们可以自己创建
class FixCharField(models.Field):
    '''
    自定义的char类型的字段类
    '''
    def __init__(self,max_length,*args,**kwargs):
        self.max_length=max_length
        super().__init__(max_length=max_length,*args,**kwargs)

    def db_type(self, connection):
        '''
        限定生成的数据库表字段类型char，长度为max_length指定的值
        :param connection:
        :return:
        '''
        return 'char(%s)'%self.max_length
#应用上面自定义的char类型
class Class(models.Model):
    id=models.AutoField(primary_key=True)
    title=models.CharField(max_length=32)
    class_name=FixCharField(max_length=16)
    gender_choice=((1,'男'),(2,'女'),(3,'保密'))
    gender=models.SmallIntegerField(choices=gender_choice,default=3)

4.DateField

Date field, the date format YYYY-MM-DD, corresponding to the Python datetime.date () instance.

5.DateTimeField

Time field, the format YYYY-MM-DD HH: MM [: ss [.uuuuuu]] [TZ], corresponding to the Python A datetime.datetime () instance.

6. Fields Collection

AutoField(Field)
    - int自增列，必须填入参数 primary_key=True

   
BigAutoField(AutoField)
    - bigint自增列，必须填入参数 primary_key=True

        注：当model中如果没有自增列，则自动会创建一个列名为id的列
        from django.db import models

        class UserInfo(models.Model):
            # 自动创建一个列名为id的且为自增的整数列
            username = models.CharField(max_length=32)

        class Group(models.Model):
            # 自定义自增列
            nid = models.AutoField(primary_key=True)
            name = models.CharField(max_length=32)

SmallIntegerField(IntegerField):
    - 小整数 -32768 ～ 32767
PositiveSmallIntegerField(PositiveIntegerRelDbTypeMixin, IntegerField)
    - 正小整数 0 ～ 32767
IntegerField(Field)
    - 整数列(有符号的) -2147483648 ～ 2147483647

PositiveIntegerField(PositiveIntegerRelDbTypeMixin, IntegerField)
    - 正整数 0 ～ 2147483647

BigIntegerField(IntegerField):
    - 长整型(有符号的) -9223372036854775808 ～ 9223372036854775807

BooleanField(Field)
    - 布尔值类型

NullBooleanField(Field):
    - 可以为空的布尔值

CharField(Field)
    - 字符类型
    - 必须提供max_length参数， max_length表示字符长度

TextField(Field)
    - 文本类型

EmailField(CharField)：
    - 字符串类型，Django Admin以及ModelForm中提供验证机制

IPAddressField(Field)
    - 字符串类型，Django Admin以及ModelForm中提供验证 IPV4 机制

GenericIPAddressField(Field)
    - 字符串类型，Django Admin以及ModelForm中提供验证 Ipv4和Ipv6
    - 参数：
protocol，用于指定Ipv4或Ipv6， 'both',"ipv4","ipv6"
unpack_ipv4， 如果指定为True，则输入::ffff:192.0.2.1时候，可解析为192.0.2.1，开启此功能，需要protocol="both"

URLField(CharField)
    - 字符串类型，Django Admin以及ModelForm中提供验证 URL

SlugField(CharField)
    - 字符串类型，Django Admin以及ModelForm中提供验证支持 字母、数字、下划线、连接符（减号）

CommaSeparatedIntegerField(CharField)
    - 字符串类型，格式必须为逗号分割的数字

UUIDField(Field)
    - 字符串类型，Django Admin以及ModelForm中提供对UUID格式的验证

FilePathField(Field)
    - 字符串，Django Admin以及ModelForm中提供读取文件夹下文件的功能
    - 参数：
                path,                      文件夹路径
                match=None,                正则匹配
                recursive=False,           递归下面的文件夹
                allow_files=True,          允许文件
                allow_folders=False,       允许文件夹

FileField(Field)
    - 字符串，路径保存在数据库，文件上传到指定目录
    - 参数：
            upload_to = ""      上传文件的保存路径
            storage = None      存储组件，默认
            
django.core.files.storage.FileSystemStorage

ImageField(FileField)
    - 字符串，路径保存在数据库，文件上传到指定目录
    - 参数：
            upload_to = ""      上传文件的保存路径
            storage = None      存储组件，默认
            
django.core.files.storage.FileSystemStorage
      width_field=None,   上传图片的高度保存的数据库字段名（字符串）
      height_field=None   上传图片的宽度保存的数据库字段名（字符串）

DateTimeField(DateField)
    - 日期+时间格式 YYYY-MM-DD HH:MM[:ss[.uuuuuu]][TZ]

DateField(DateTimeCheckMixin, Field)
    - 日期格式      YYYY-MM-DD

TimeField(DateTimeCheckMixin, Field)
    - 时间格式      HH:MM[:ss[.uuuuuu]]

DurationField(Field)
    - 长整数，时间间隔，数据库中按照bigint存储，ORM中获取的值为datetime.timedelta类型

FloatField(Field)
    - 浮点型

DecimalField(Field)
    - 10进制小数
    - 参数：
            max_digits，小数总长度
            decimal_places，小数位长度

BinaryField(Field)
    - 二进制类型

Third, the correspondence relationship between fields in ORM and MySQL

    'AutoField': 'integer AUTO_INCREMENT',
    'BigAutoField': 'bigint AUTO_INCREMENT',
    'BinaryField': 'longblob',
    'BooleanField': 'bool',
    'CharField': 'varchar(%(max_length)s)',
    'CommaSeparatedIntegerField': 'varchar(%(max_length)s)',
    'DateField': 'date',
    'DateTimeField': 'datetime',
    'DecimalField': 'numeric(%(max_digits)s, %(decimal_places)s)',
    'DurationField': 'bigint',
    'FileField': 'varchar(%(max_length)s)',
    'FilePathField': 'varchar(%(max_length)s)',
    'FloatField': 'double precision',
    'IntegerField': 'integer',
    'BigIntegerField': 'bigint',
    'IPAddressField': 'char(15)',
    'GenericIPAddressField': 'char(39)',
    'NullBooleanField': 'bool',
    'OneToOneField': 'integer',
    'PositiveIntegerField': 'integer UNSIGNED',
    'PositiveSmallIntegerField': 'smallint UNSIGNED',
    'SlugField': 'varchar(%(max_length)s)',
    'SmallIntegerField': 'smallint',
    'TextField': 'longtext',
    'TimeField': 'time',
    'UUIDField': 'char(32)',

Fourth, field parameters

1.null

Is used to represent the contents of a field may be empty

2.unique

If set unique = True, then the field in this table must be unique

3.db_index

If db_index = True represents the index field is set for this purpose.

4.DateField和DateTimeField

auto_now_add

Configuring auto_now_add = True, create a data record when the current time will be added to the database.

auto_now

Configuration auto_now = True, each time when updating the data record will update the field.

Fifth, the relationship field

5.1 foreign key (a ForeignKey)

Foreign key is used to indicate the type of the foreign key relationship in the ORM, generally one of the fields provided ForeignKey 'many' in 'multiple' of.

ForeignKey can make tables and other relationships at the same time and can also make their own relationships.

Field parameters

to : Set the table to be associated

to_field : Sets the table associated field

on_delete behavior of the line when you delete data associated with the table, the current table associated with it:

models.CASECADE : delete the associated data, also associated with deleted

db_constraint：

The remaining field parameters

models.DO_NOTHING
删除关联数据，引发错误IntegrityError

models.PROTECT
删除关联数据，引发错误ProtectedError

models.SET_NULL
删除关联数据，与之关联的值设置为null（前提FK字段需要设置为可空）

models.SET_DEFAULT
删除关联数据，与之关联的值设置为默认值（前提FK字段需要设置默认值）

models.SET

删除关联数据，
a. 与之关联的值设置为指定值，设置：models.SET(值)
b. 与之关联的值设置为可执行对象的返回值，设置：models.SET(可执行对象)

Delete the associated data example

def func():
    return 10

class MyModel(models.Model):
    user = models.ForeignKey(
        to="User",
        to_field="id"，
        on_delete=models.SET(func)
    )

5.2 one relationship field (OneToOneField)

Usually one field to extend the existing field. (Popular to say that all the information a person not on a table inside, a simple message information from another table, privacy tables, by one foreign key associations between)

Field parameters

to : Set the table to be associated.

to_field : Sets the table associated field

on_delete behavior of the line when you delete data associated with the table, the current table associated with it:

General Operation --- python script test

First look at the configuration parameters during normal operation, so that we can run our test scripts directly in Django page

Call Django environment in python script: This will run test.py file to run the test directly

Added: can create a test file for each application, and then configure Django environment