Advanced Usage

Utility Methods

These are available on your model instance when the mixin or extend the base model is used.

Method	Details
has_changed(field_name: str) -> bool	Return a boolean indicating whether the field's value has changed since the model was initialized, or refreshed from db
initial_value(field_name: str) -> bool	Return the value of the field when the model was first initialized, or refreshed from db

Example

You can use these methods for more advanced checks, for example:

from django_lifecycle import LifecycleModel, AFTER_UPDATE, hook


class UserAccount(LifecycleModel):
    first_name = models.CharField(max_length=100)
    last_name = models.CharField(max_length=100)
    email = models.CharField(max_length=100)
    marital_status = models.CharField(max_length=100)

    @hook(AFTER_UPDATE)
    def on_name_change_heck_on_marital_status(self):
        if (
            self.has_changed('last_name') 
            and not self.has_changed('marital_status')
        ):
            send_mail(
                to=self.email, 
                "Has your marital status changed recently?"
            )

Custom conditions

Custom conditions can be created as long as they respect condition signature

def changes_to_ned_flanders(instance, update_fields=None) -> bool:
    return (
        instance.has_changed("first_name") 
        and instance.has_changed("last_name")
        and instance.first_name == "Ned"
        and instance.last_name == "Flanders"
    )

To allow your custom conditions to be chainable, create a class based condition inheriting ChainableCondition.

from django_lifecycle import BEFORE_SAVE
from django_lifecycle.conditions import WhenFieldHasChanged
from django_lifecycle.conditions.base import ChainableCondition


class IsNedFlanders(ChainableCondition):
    def __call__(self, instance, update_fields=None):
        return (
            instance.first_name == "Ned" 
            and instance.last_name == "Flanders"
        )


@hook(
    BEFORE_SAVE,
    condition=(
        WhenFieldHasChanged("first_name")
        & WhenFieldHasChanged("last_name")
        & IsNedFlanders()
    )
)
def foo():
    ...

Suppressing Hooked Methods

To prevent the hooked methods from being called, pass skip_hooks=True when calling save:

   account.save(skip_hooks=True)