Abstract Model

Introduction

While I was creating letsh application, I thought that there must be some data that could be shared throughout data no matter what they are. The best example for this could be time that data was newly created or updated. If I include these data, then admin users later will be able to easily control over those data based on those time data.

However, including all these common data into all other apps' models is just repeating codes ourselves and it could waste our DB. So it would be very effective to make these types of models that do not wasting too much DB space and can be used in other models.

Django is also suggesting DRY(Do NOT Repeat Yourself) (opens in a new tab), so let's keep our code more sexier!

This is where abstract model (opens in a new tab) is used. After I defined the common data fields, with class inheritance (opens in a new tab) other apps' models can also use Common model's data fields.

Initialization

To get start with creating an abstract model, I created common/ app in my project root route.

django-admin startapp common

Then included my app in INSTALLED_APPS (opens in a new tab) 내부에 설치해준다.

config/settings.py

INSTALLED_APPS = [
  # ...
  "common.apps.CommonConfig",
]

`CommonDateModel`

CommonDateModel is an abstract model for representing date. This model will be occasionally used where date data is needed.

Date that user left comment
Date that user created its own wishlist
Date that user created reservation (check-in & check-out)

Creating Model Class

I created CommonDateModel model class.

from django.db import models
class CommonDateModel(models.Model):
    """Common Date Model Definition"""
    pass

`Meta` Class Configuration

Meta class (opens in a new tab) allows us to do extra configuration on the model. As models in common/ app are abstract models, I set abstract = True as shown in documentaiton (opens in a new tab).

By doing this, it won't create tables in DB separately but still be able to use those abstract model fields in other models as well.

from django.db import models
class CommonDateModel(models.Model):
    """Common Date Model Definition"""
    pass
    class Meta:
        abstract = True

`DateField`

Lastly I set fields.

DateField (opens in a new tab) is a field that literally controls with date. I set date created as created_date, and date updated as updated_date, respectively.

Here, auto_now_add (opens in a new tab) attribute is used when an object is automatically created as current date.

On the other hand, auto_now (opens in a new tab) attribute is used when object is updated and set update date as current date automatically.

from django.db import models
class CommonDateModel(models.Model):
    """Common Date Model Definition"""
    created_date = models.DateField(auto_now_add=True, verbose_name=_("Created Date"))
    updated_date = models.DateField(auto_now=True, verbose_name=_("Updated Date"))
    class Meta:
        abstract = True

Creating Model Class

I created CommonDateModel model class.

`Meta` Class Configuration

By doing this, it won't create tables in DB separately but still be able to use those abstract model fields in other models as well.

`DateField`

Lastly I set fields.

DateField (opens in a new tab) is a field that literally controls with date. I set date created as created_date, and date updated as updated_date, respectively.

Here, auto_now_add (opens in a new tab) attribute is used when an object is automatically created as current date.

On the other hand, auto_now (opens in a new tab) attribute is used when object is updated and set update date as current date automatically.

from django.db import models
class CommonDateModel(models.Model):
    """Common Date Model Definition"""
    pass

`CommonDateTimeModel`

I followed exact same logic as I did above for CommonDateModel. The only difference is that since this model will control over both date and time, I used DateTimeField (opens in a new tab). This abstract model will be used in which models that require more precise date and time.

Date and time when user created reservation
Date and time when user created payment
Date and time when user created abuse report

common/models.py

class CommonDateTimeModel(models.Model):
    """Common Date Time Model Definition"""
    created_at = models.DateTimeField(
        auto_now_add=True, verbose_name=_("Created Date & Time")
    )
    updated_at = models.DateTimeField(
        auto_now=True, verbose_name=_("Updated Date & Time")
    )
    class Meta:
        abstract = True

Result

If we add field defined in abstract base model in other apps' admin.py, we can see it is nicely put into admin panel as below.

But then if we take a look at common/ app's database, we can find out that there has been no migration happened for TimeStampModel (See blue bracket). By doing this, we can effectively manage database.

User Model Rooms Model

Abstract Model

Introduction

Initialization

CommonDateModel

Creating Model Class

Meta Class Configuration

DateField

Creating Model Class

Meta Class Configuration

DateField

CommonDateTimeModel

Result

`CommonDateModel`

`Meta` Class Configuration

`DateField`

`Meta` Class Configuration

`DateField`

`CommonDateTimeModel`