CODEWITHSUNDEEP
pythondjangodatabasepostgresqlmigration
Basel J. Hamadeh
Basel J. Hamadeh

Reputation: 985

Adding a Non-Primary Key AutoField or a 'serial' field in a Django Model which uses a UUID field as a Primary Field

I am building a Model with a UUIDField as the Primary Key. But my use case requires. having an Auto Increment field as well. Django provides an AutoField. But it is required to have primary_key=True which in my case something I don't want as I am using the UUIDField as primary_key.

I tried creating a field and giving db_type of 'serial' and adding a migration which alters the sequence to restart at 100000.. Adding an object to the database using the Admin will always store the number field as null value. and if I remove null=True. Then the save will fail as it will require a value for the number field.

How can I make the number field incremental while keeping the UUIDField as a primary key ?

fields.py

class SerialField(models.Field):
    description = _("BIGINT UNSIGNED NOT NULL AUTO_INCREMENT UNIQUE")

    empty_strings_allowed = False

    default_error_messages = {
        'invalid': _("'%(value)s' value must be an integer."),
    }

    def __init__(self, *args, **kwargs):
        kwargs['blank'] = True
        super().__init__(*args, **kwargs)

    def db_type(self, connection):
        return 'serial'

models.py

from .fields import SerialField

class MyModel(models.Model):
    uuid = models.UUIDField(
        verbose_name=_("UUID Identifier"),
        primary_key=True,
        default=uuid.uuid4,
        editable=False,
        help_text=_("Requried, PrimaryKey none-editable"),
        db_index=True,
    )
    number = SerialField(
        primary_key=False,
        editable=False,
        help_text=_("Auto Increment Number"),
        verbose_name=_("Number"),
        #null=True
    )

0002_auto_20180202.py from django.db import migrations

def forwards(apps, schema_editor):
    if schema_editor.connection.alias == 'default':
        return migrations.RunSQL(
            "ALTER SEQUENCE app_name_mymodel_number_seq RESTART WITH 100000"
        )


class Migration(migrations.Migration):

    dependencies = [
        ('activities', '0001_initial'),
    ]

    operations = [
        migrations.RunPython(forwards)
    ]

Upvotes: 11

Views: 4711

Answers (2)

user3785966
user3785966

Reputation: 2978

For the sake of example, lets assume the name of our table is payouts

Below will be the model for payouts:

class Payouts(models.Model):
    # seq_id = models.IntegerField() 
    # we will create seq_id auto-increment by raw SQL
    id = models.UUIDField(primary_key=True)

    class Meta:
        managed = True
        db_table = 'payouts'

You can see that we want to have id with uuid as primary key.

Follow the instructions below:

Step 1: Make migrations file for the model above.

python manage.py makemigrations

Step 2: Generate an empty migration to execute SQL queries:

python manage.py makemigrations  --empty -n dont_delete_add_defaults_sql

Step 3: Edit dont_delete_add_defaults_sql as below:

from django.db import migrations    

class Migration(migrations.Migration):

    dependencies = [
        ('apiapp', '0001_initial'), #Replace 0001_initial with the name of file generated in step 1
    ]

    operations = [
        migrations.RunSQL("ALTER TABLE payouts ADD seq_id serial NOT NULL;"),
        migrations.RunSQL("DROP SEQUENCE IF EXISTS payouts_seq_id_seq CASCADE;"),
        migrations.RunSQL("create sequence payouts_seq_id_seq owned by payouts.seq_id;"),
        migrations.RunSQL("alter table payouts alter column seq_id set default nextval('payouts_seq_id_seq');"),
    ]

Step 4: Run the final migrations

python manage.py migrate

Upvotes: 0

SebastianR
SebastianR

Reputation: 51

Tried this as well. My workaround was to use raw SQL instead.

Migration:

migrations.RunSQL(
    "CREATE SEQUENCE sequence_name START 100000",
    reverse_sql="DROP SEQUENCE IF EXISTS sequence_name",
    elidable=False,
),

Model: 

def get_next_increment():
    with connection.cursor() as cursor:
        cursor.execute("SELECT nextval('sequence_name')")
        result = cursor.fetchone()
        return result[0]

class MyModel(models.Model):
    my_field = models.IntegerField(default=get_next_increment, editable=False, unique=True)

Upvotes: 4

Related Questions