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ORM Advanced - Coggle Diagram

- - - - You can specify default objects ordering using the Meta class:
        class Item(models.Model):
        name = models.CharField(max_length=63)
        serial_number = models.IntegerField()
        class Meta:
        ordering = ["-serial_number"]
    - - A human-readable name for the object, singular (you will see this name in the Django admin panel later):
        verbose_name = "item"
        If it isn’t provided, Django uses a munged version of the class name —CamelCase becomes camel case.
    - - It is a plural name for an object. By default, Django will use verbose_name + "s". And it’s not convenient sometimes. For example, your model name is Bus, then verbose_plural_name is the buss, and we need to change it:
        verbose_name_plural = "buses"
    - - The name of the database table to use for the model:
        db_table = "items_db"
        Django will automatically choose the name of the database table based on the name of your model class and the app it is contained in, saving you time.
    - - Індексування -
        це як створення організованої дорожньої карти для бази даних, щоб швидше знаходити записи.
        Вона передбачає створення відсортованої структури, яка вказує на точне місцезнаходження записів на основі певних полів - B-Tree.
        Бінарний пошук за цим індексом дозволяє швидко та ефективно знаходити конкретні записи.
        Такий підхід до індексування значно прискорює процес пошуку інформації в базах даних, особливо при роботі з великими обсягами даних.
        
        class Item(models.Model): name = models.CharField(max_length=63) serial_number = models.IntegerField() class Meta: indexes =[ models.Index(fields=["serial_number"]) ]
        
        Time complexity
        
        Without idexes:
        Find: O(N)
        Insert: O(1)
        
        With idexes:
        Find: O(logN)
        Insert: O(logN)
    - - UniqueConstraint
        
        Imagine that you want 2 fields from the model to be unique together. You should use the UniqueConstraint to do this:
        
        class Meta: constraints = [ UniqueConstraint(fields=["name", "serial_number"]) ]
      - CheckConstraint
        
        It creates a check constraint in the database. Imagine that you want only store items with serial numbers greater than 18 and lower than 20000.
        Also, you can specify the constraint name using the name parameter (should be unique).
        
        class Meta: constraints = [ CheckConstraint( check=Q(serial_number__gte=18) & Q(serial_number__lte=20000), name="serial_number_constraint"), ]
    - - A unit you want to manage as "a whole" is a transaction. It takes place either entirely or not at all.
      - ACID
        stands for 4 core requirements for database transactions:
        
        atomicity
        guarantees that each transaction is treated as a single "unit", which either succeeds completely or fails completely if any of the statements constituting a transaction fails;
        
        consistency
        ensures that the data state before and after the transaction is consistent. For example, we expect the total amount of money on the 2 bank accounts to remain the same after the money is transferred from one account to another. The consistency rule will be violated if the money is gone from the first account but is not added to the second account;
        
        isolation
        ensures that if multiple transactions are executed concurrently, they do not affect each other, and the database is left in the same state as if the transactions were executed sequentially;
        
        durability
        guarantees that once a transaction has been committed, it will remain committed even if your system fails (for example, power problems or some crashes).
        
        You can use the following steps to create a transaction in Django:
        from django.db import transaction
        with transaction.atomic():
    - - як користуватися вбудованим в Django ORM User
        (третє відео з кінця)
      - User create/update
        (друге відео з кінця)