[ORM framework]

Django ORM frame

Definition

• Map classes to data tables
• Through classes and objects, you can manipulate the data in its corresponding data table （CRUD)

step

• Configure the database connection information
  - Create databases and users
  - Configuration database
  - install mysqlclient

• In the subapplication of models.py Define model classes in

  • Generally in sub applications models.py Define model classes in
  • Model classes must inherit Model Class or Model Subclasses of
  • Define attributes in the model class （ It has to be for Field Subclass ), Equivalent to fields in the data table
  • CharField–> varchar
  • IntegerField–> integer
  • BooleanField–>bool

class Animal(models.Model):
   name = models.CharField(max_length=32)
   age = models.IntegerField()
   gender = models.BooleanField()
   
   class Meta:
       managed = True

Examples

1. Define model classes

class Projects(models.Model):
    """ max_length: Must pass parameters  verbose_name: When rendering forms , There will be a Chinese description below ： Project name ;  The background management site will also add a description to the current field  help_text: stay api The interface document will be used as Chinese description information  unique=True:  Represents setting unique constraints on a field , The default is False default: Specify default  TextField()： Support long text  blank=True： Allow empty string ,DRF Valid only when deserializing input  null = Tru： Allow for null,DRF Valid only when deserializing input  DateTimeField Appoint auto_now_add=True, When creating a record, the time will be automatically created as the value of this field , Subsequent updates will not change this value  DateTimeField Appoint auto_now=True, When updating a record , The time of updating the record will be automatically taken as the value of this field  """
    name = models.CharField(max_length=50,
                            verbose_name=' Project name ',
                            help_text=' Project name ',
                            unique=True)
    leader = models.CharField(max_length=10,
                              verbose_name=' Project leader ',
                              help_text=' Project leader ')
    # default=xxx Specify default 
    is_execute = models.BooleanField(verbose_name=' Whether to start the project ',
                                     help_text=' Whether to start the project ',
                                     default=False)
    # TextField() Support long text 
    # blank=True, Allow empty string  
    # null = True, Allow for null
    desc = models.TextField(verbose_name=' Project description information ',
                            help_text=' Project description information ',
                            blank=True, null=True, default='')
    # DateTimeField Appoint auto_now_add=True, When creating a record, the time will be automatically created as the value of this field , Subsequent updates will not change this value 
    create_time = models.DateTimeField(auto_now_add=True, 
                                       verbose_name=' Creation time ', 
                                       help_text=' Creation time ')
    # DateTimeField Appoint auto_now=True, When updating a record , The time of updating the record will be automatically taken as the value of this field 
    update_time = models.DateTimeField(auto_now=True, 
                                       verbose_name=' Update time ', 
                                       help_text=' Update time ')
    #  Modify the meta information of the model class 
    class Meta:
        # #  Whether it is managed 
        # managed = True
        # db_table: Specified table name 
        db_table = 'tb_projects'

2. transfer

terminal Execute the command in the project root ：

#  Migrate all sub applications 
python manage.py makemigrations
python manage.py migrate
#  Migrate the specified sub application 
python manage.py makemigrations  Subapplication name 
python manage.py migrate  Subapplication name 

The default name of the generated data table is ： Subapplication name _ The model class name is lowercase

#  View the generated migration script native sql sentence 
python manage.py sqlmigrate  Subapplication name (projects)  Migration script name (0002_projects)

• Complete the database addition, deletion, modification and query operations through classes and objects

ORM Object composition

a. database ：  You need to manually create the database in advance 
b. Data sheet ： And ORM In the frame models.py Model classes in correspond one by one 
c. Field ： Class attributes in model classes 
d. Record ： Similar to multiple instances of model classes 

Global profile settings.py Middle configuration database

ORM Modify the existing field names in the table

When we modify a field name or add a new field in the online database , Before deleting fields , All existing data should be backed up , Can be cold standby , It can be hot standby ;

• Cold standby ：mysqldumps Orders can be made for cold standby

ORM Modify existing fields ：

• Modify the field name in the model class （ Generally, it can't be modified id Primary key ）

• Re execute the migration script

    - python manage.py makemigrations  Subapplication name 
    - python manage.py migrate  Subapplication name