Detailed explanation of ORM in Django (Latest recommendation)

from  import models
class ForeignKey():
    pass
class ForeignMany():
    pass
class Event():
    # int autoincrement column, the parameter primary_key=True must be filled in.  When no primary key is specified in the model, django will automatically create a column with the column name id as the primary key.    a = (primary_key=True)  # Primary key    # The most commonly used field must specify the max_length character length    b = (max_length=24, null=False)  # Project Name    # There is a difference between Boolean and NullBooleanField, True/False, this type does not allow null.    c = (default=True)  # Is it valid    # Can be null boolean    d = (default=True)  # Whether to display    # json type    e = ()  # Event details    # UUID
    f = ()
    # Small integer - 32768 ~ 32767    g = ()
    # Positive small integer 0 ~ 32767    h = ()
    # integer sequence (signed) -2147483648 ~ 2147483647    i = ()
    # Positive integer 0 ~ 2147483647    j = ()
    # Long integer (signed) -9223372036854775808 ~ 9223372036854775807    k = ()
    # Long integer, time interval, stored in the database according to bigint, the value obtained in the ORM is of type    l = ()
    #Floating point type    m = ()
    # Amount type->100.12    n = (max_digits=5, decimal_places=2)
    # Binary type    o = ()
    # One to Many    p = (to=ForeignKey,  # Related to the table                          to_field='project_id',  # The field of the associated table can be associated with the primary key of the associated table without specifying it.                          db_constraint=False,  # Whether to generate foreign key constraints (default is True)                          related_name="_project_id",  # Reverse query name                          on_delete=,  # Associate Delete Options                          db_column='project_id',  # Set the name in the table                          help_text='project_id associated to Event table',  # Description field will be displayed in the admin background and will not be synchronized to the database                          )
    # One-to-one, and one-to-many systems, only by default unique=True is added    q = (to=ForeignKey,  # Related to the table                             to_field='project_id',  # The field of the associated table can be associated with the primary key of the associated table without specifying it.                             db_constraint=False,  # Whether to generate foreign key constraints (default is True)                             related_name="_project_id",  # Reverse query name                             on_delete=,  # Associate Delete Options                             db_column='project_id',  # Set the name in the table                             help_text='project_id associated to Event table',  # Description field will be displayed in the admin background and will not be synchronized to the database                             )
    # Many to many    # Create a third table manually. Although you can use orm's query method, add(), set(), remove(), and clear() are not supported.    r = (to='ForeignKey',  # Related to that table, that is, associated with that table                               through='ForeignMany',  # Customize the third table, you can automatically generate the third table without setting it.                               through_fields=('book', 'author')  # Customize the two fields in the third table to manage the main table and the associated table without setting                               )
    # Create time, when creating data records, the current time will be added to the database.    s = (auto_now_add=True)
    # Modify time, this field will be updated every time the data record is updated.    t = (auto_now=True)
class Meta:
    # The default table name of the model in the database is APP name_class name, and the default value can be re-defaulted through db_table, which is equivalent to the indication of the specified model in the database.    db_table = 'project_event'

class Classes():
    name = (max_length=32)
class Student():
    name = (max_length=32)
    theclass = (to="Classes")

().student_set.all()

class Student():
    name = (max_length=32)
    theclass = (to="Classes", related_name="students")

().()

class Person():
    name = (max_length=16)
    friends = ("self")

class Person():
    name = (max_length=16)
    friends = ("self", symmetrical=False)

class Book():
    title = (max_length=32, verbose_name="Book Title")
class Author():
    name = (max_length=32, verbose_name="Author's Name")
# Create the third table by yourself, and associate the book and the author through foreign keys respectivelyclass Author2Book():
    author = (to="Author")
    book = (to="Book")
    class Meta:
        unique_together = ("author", "book")

class Book():
    title = (max_length=32, verbose_name="Book Title")
# Automatically create a third table through the ManyToManyField built into ORMclass Author():
    name = (max_length=32, verbose_name="Author's Name")
    books = (to="Book", related_name="authors")

class Book():
    title = (max_length=32, verbose_name="Book Title")
# Create the third table yourself and specify the association through ManyToManyFieldclass Author():
    name = (max_length=32, verbose_name="Author's Name")
    books = (to="Book", through="Author2Book", through_fields=("author", "book"))
    # through_fields accepts a 2 tuple ('field1', 'field2'):    # where field1 is the author of the foreign key of the model that defines ManyToManyField, and field2 is the foreign key name of the associated target model (book).class Author2Book():
    author = (to="Author")
    book = (to="Book")
    class Meta:
        unique_together = ("author", "book")

class Meta:
    #app_label declaration belongs to which application    app_label='Grade_manager'
    #table_name Custom table name, if the table name is not specified, it will be: Application name_Class name    db_table='grade'
    #Some databases have database tablespaces, such as Oracle.  You can use db_tablespace to specify which database table space the corresponding database table of this model is placed in.    db_tablespace = "user"
    #DateField or DateTimeField fields names. If this option is provided, the module will have a get_latest() function to get the "latest" object (based on that field): get the last order_date field record,    get_latest_by = "order_date"   
    #Give this model a simpler and easier to read    verbose_name = "pizza"        
    What is the plural form of the # model    verbose_name_plural
    # Joint Index    index_together=("grade","user")
    # Specify the default field sorting. Only when this property is set can the result we query be reverse().    ordering="grade"

from  import models
class Person():
    first_name = (max_length=30)
    last_name = (max_length=30)

CREATE TABLE myapp_person (
    "id" serial NOT NULL PRIMARY KEY,
    "first_name" varchar(30) NOT NULL,
    "last_name" varchar(30) NOT NULL
);

DATABASES = {
    "default": {
        "ENGINE": "",
        "NAME": "Your database name",  # You need to create a database manually        "USER": "Database username",
        "PASSWORD": "Database Password",
        "HOST": "databaseIP",
        "POST": 3306
    }
}

import pymysql
pymysql.install_as_MySQLdb()

class UnsignedIntegerField():
    def db_type(self, connection):
        return 'integer UNSIGNED'

class FixedCharField():
    """
     Custom char type field class
     """
    def __init__(self, max_length, *args, **kwargs):
        super().__init__(max_length=max_length, *args, **kwargs)
         = max_length
    def db_type(self, connection):
        """
         The field type that qualifies the generated database table to be char and the length is the value specified by length
         """
        return 'char(%s)' % 
class Class():
    id = (primary_key=True)
    title = (max_length=25)
    # Use the fields of type char as customized above    cname = FixedCharField(max_length=25)

# Get all book objects, the result is an object list()  
# Get the object that meets the criteria(**kwargs)  
# Filter all those that meet the criteria, the result is an object list(**kwargs)  
# Filter out all those that do not meet the criteria, and the result is an object list. There has always been a question in this place. It seems that if the foreign key is excluded, it will not work.(**kwargs)  
# Dictionary list [{id:1,name:20},{id:2,name:18} ], values('id') are not specified in brackets, and only the specified ones are displayed if specified, [{id:1},{id:2,}]().values("id","name")  
# Tuple list, [ (1,20), (2,18)] is the same as above, displays the specified content when specified().values_list("id","name")  
# Arrange in ascending order by id().order_by("id")  
# Arrange in descending order of id().order_by("-id")  
# First, arrange the same age by id in descending order.().order_by("age", "-id") 
# Invert the result; Note that the reverse must be sorted before, otherwise the reverse will be invalid; or specify ordering=("id", ) in the meta in the Book class in the file. Note that the comma must have().order_by("id").reverse()  
# Deduplication, when the obtained result appears multiple times when the same object in the Queryset list is deduplication, only one().values("id","name").distinct():  
# Count, you can count the number of results, such as counting the number of elements in Queryset.().count() 
# Get the first item in the result, even if the previous result list is empty, there will be no error().first()  
# Get the last one in the result().last()  
# Determine whether there is something in the Queryset list, and the result is True or False;().exists() 

# Conditional query.  (You can connect multiple conditions through commas) Return the QuerySet query set (can be traversed)# __exact equals.  __exact can be omitted.  (__iexact is case-insensitive)(title__exact='The Eight Tribes of the Heavenly Dragon')
# Equivalent (title__exact='Tianlong Bashi')(title='The Eight Tribes of the Heavenly Dragon')
# __contains Contains.  Fuzzy query.  (__icontains is case-insensitive)(title__contains='sky')
# __endswith ends with...  __startswith starts with...  (__iendswith is case-insensitive)(title__endswith='department')
# __isnull Whether it is empty.  True: Expressed as null.  False means not null.(title__isnull=False)
# __in Range query.(id__in=[1, 3, 5])
# __range range query, query ids from 1 to 5(id__range=[1, 5])
# greater than less than(id__gt=3)  # Greater than(id__lt=3)  # Small(id__gte=3)  # greater than or equal to(id__lte=3)  # Less than or equal to# Date query, where __gt, __lt, __gte, and __lte all use dates(pub_date__gt=date(1980, 1, 1))
# Date query(pub_date__year=1980)  # Year(pub_date__month=1980)  # moon(pub_date__day=1980)  # day(pub_date__week_day=1980)  # Weekly(pub_date__hour=1980)  # hour(pub_date__minute=1980)  # point(pub_date__second=1980)  # Second