Django model 학습 키워드

• Field type : CharField
• Field option : null vs blank, choices, default, primary_key, unique
• Relationships : Many-to-one, Many-to-many, One-to-one
• Extra fileds on many-to-many
• Meta option : ordering, verbose_name, db_table
• Model method : 아래 참조

1) Verbose field name

• Each field type, except for ForeignKey, ManyToManyField and OneToOneField, takes an optional first positional argument – a verbose name.
• If the verbose name isn’t given, Django will automatically create it using the field’s attribute name, converting underscores to spaces.

# verbose name => "first name"
first_name = models.CharField(max_length=30)

# verbose name => "persone's first name"
first_name = models.CharField("person's first name", max_length=30)

• ForeignKey, ManyToManyField and OneToOneField require the first argument to be a model class, so use the verbose_name keyword argument:

poll = models.ForeignKey(
    Poll,
    on_delete=models.CASCADE,
    verbose_name="the related poll",
)

2) Model method

• Define custom methods on a model to add custom “row-level” functionality to your objects. Whereas Manager methods are intended to do “table-wide” things, model methods should act on a particular model instance.
• This is a valuable technique for keeping business logic in one place – the model.

from django.db import models

class Person(models.Model):
    first_name = models.CharField(max_length=50)
    last_name = models.CharField(max_length=50)
    birth_date = models.DateField()

    def baby_boomer_status(self):
        "Returns the person's baby-boomer status."
        import datetime
        if self.birth_date < datetime.date(1945, 8, 1):
            return "Pre-boomer"
        elif self.birth_date < datetime.date(1965, 1, 1):
            return "Baby boomer"
        else:
            return "Post-boomer"

    @property
    def full_name(self):
        "Returns the person's full name."
        return '%s %s' % (self.first_name, self.last_name)

2-1) Overriding predefined model methods

• There’s another set of model methods that encapsulate a bunch of database behavior that you’ll want to customize. In particular you’ll often want to change the way save() and delete() work.
• You’re free to override these methods (and any other model method) to alter behavior.
• A classic use-case for overriding the built-in methods is if you want something to happen whenever you save an object. For example (see save() for documentation of the parameters it accepts):

from django.db import models

class Blog(models.Model):
    name = models.CharField(max_length=100)
    tagline = models.TextField()

    def save(self, *args, **kwargs):
        do_something()
        super().save(*args, **kwargs)  # Call the "real" save() method.
        do_something_else()