diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 24ff476..3f88db2 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -56,4 +56,4 @@ jobs:
 
       - name: Run tests
         # For example, using `pytest`
-        run: uv run pytest test
+        run: uv run pytest
diff --git a/README.rst b/README.rst
index 934cae0..63ae779 100644
--- a/README.rst
+++ b/README.rst
@@ -27,3 +27,9 @@ ____________
 
 3. Run `python manage.py migrate` to create the enumeration models.
 
+
+
+Development
+____________
+
+DJANGO_SETTINGS_MODULE=enumeration.tests.settings django-admin makemigrations
\ No newline at end of file
diff --git a/pytest.ini b/pytest.ini
index 68e1ddb..076f7f2 100644
--- a/pytest.ini
+++ b/pytest.ini
@@ -1,3 +1,3 @@
 [pytest]
-DJANGO_SETTINGS_MODULE = test.settings
-pythonpath = . src
\ No newline at end of file
+DJANGO_SETTINGS_MODULE = enumeration.tests.settings
+pythonpath = src
\ No newline at end of file
diff --git a/src/enumeration/migrations/0002_alter_counter_id_alter_gap_id_alter_sequence_id.py b/src/enumeration/migrations/0002_alter_counter_id_alter_gap_id_alter_sequence_id.py
new file mode 100644
index 0000000..cf2a1e9
--- /dev/null
+++ b/src/enumeration/migrations/0002_alter_counter_id_alter_gap_id_alter_sequence_id.py
@@ -0,0 +1,34 @@
+# Generated by Django 4.2.17 on 2024-12-09 04:14
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("enumeration", "0001_initial"),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name="counter",
+            name="id",
+            field=models.BigAutoField(
+                auto_created=True, primary_key=True, serialize=False, verbose_name="ID"
+            ),
+        ),
+        migrations.AlterField(
+            model_name="gap",
+            name="id",
+            field=models.BigAutoField(
+                auto_created=True, primary_key=True, serialize=False, verbose_name="ID"
+            ),
+        ),
+        migrations.AlterField(
+            model_name="sequence",
+            name="id",
+            field=models.BigAutoField(
+                auto_created=True, primary_key=True, serialize=False, verbose_name="ID"
+            ),
+        ),
+    ]
diff --git a/src/enumeration/mixins.py b/src/enumeration/mixins.py
new file mode 100644
index 0000000..19458ef
--- /dev/null
+++ b/src/enumeration/mixins.py
@@ -0,0 +1,70 @@
+from django.db import models
+from typing import Dict, TYPE_CHECKING
+from enumeration.manager import get_number, format_number, ResetPeriod, truncate_date
+
+if TYPE_CHECKING:
+    from enumeration.models import Sequence
+
+
+class EnumeratedModelMixin(models.Model):
+    sequence = models.ForeignKey(
+        "enumeration.Sequence", null=True, on_delete=models.PROTECT
+    )
+
+    number = models.CharField(max_length=255, null=True, blank=True, db_index=True)
+    position = models.PositiveIntegerField(null=True)
+    counter = models.ForeignKey(
+        "enumeration.Counter", null=True, on_delete=models.PROTECT
+    )
+
+    def get_sequence(self) -> "Sequence":
+        raise NotImplementedError
+
+    def get_enumeration_context(self) -> Dict:
+        return {}
+
+    def assign_number(self):
+        if self.number:
+            raise RuntimeError("Number present")
+
+        if not self.sequence:
+            self.sequence = self.get_sequence()
+
+        self.number, self.position, self.counter_id = get_number(
+            sequence=self.sequence, **self.get_enumeration_context()
+        )
+
+    def reassign_number(self):
+        assert self.sequence and self.position and self.counter
+        ctx = self.get_enumeration_context()
+
+        # Sequecne never resets
+        if self.sequence.reset_period == ResetPeriod.NEVER:
+            # And correct counter
+            if self.counter.period is None:
+                self.number = format_number(
+                    self.sequence.format,
+                    position=self.position,
+                    **ctx,
+                )
+                return
+        # sequnce resets
+        else:
+            # and correct counter period
+            if self.counter.period == truncate_date(
+                self.sequence.reset_period, ctx["date"]
+            ):
+                self.number = format_number(
+                    self.sequence.format,
+                    position=self.position,
+                    **ctx,
+                )
+                return
+
+        # get new number
+        self.number, self.position, self.counter_id = get_number(
+            sequence=self.sequence, **ctx
+        )
+
+    class Meta:
+        abstract = True
diff --git a/src/enumeration/models.py b/src/enumeration/models.py
index a16af68..c319694 100644
--- a/src/enumeration/models.py
+++ b/src/enumeration/models.py
@@ -1,6 +1,5 @@
 from django.core.exceptions import ValidationError
 from django.db import models
-
 from enumeration.const import ResetPeriod
 from enumeration.validators import validate_format
 
@@ -43,12 +42,3 @@ class Gap(models.Model):
     position = models.PositiveIntegerField()
 
     unique_together = ("counter", "position")
-
-
-# class EnumeratedDocumentMixin(models.Model):
-#     sequence = models.ForeignKey(Sequence)
-#     position = models.PositiveIntegerField(null=True)
-#     number = models.CharField(max_length=255, null=True, blank=True)
-#
-#     class Meta:
-#         abstract = True
diff --git a/test/__init__.py b/src/enumeration/tests/__init__.py
similarity index 100%
rename from test/__init__.py
rename to src/enumeration/tests/__init__.py
diff --git a/src/enumeration/tests/apps.py b/src/enumeration/tests/apps.py
new file mode 100644
index 0000000..d20c499
--- /dev/null
+++ b/src/enumeration/tests/apps.py
@@ -0,0 +1,6 @@
+from django.apps import AppConfig
+
+
+class TestConfig(AppConfig):
+    name = "enumeration.tests"
+    label = "enumeration_tests"
diff --git a/src/enumeration/tests/migrations/0001_initial.py b/src/enumeration/tests/migrations/0001_initial.py
new file mode 100644
index 0000000..f82cc6a
--- /dev/null
+++ b/src/enumeration/tests/migrations/0001_initial.py
@@ -0,0 +1,57 @@
+# Generated by Django 4.2.17 on 2024-12-09 04:14
+
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    initial = True
+
+    dependencies = [
+        ("enumeration", "0002_alter_counter_id_alter_gap_id_alter_sequence_id"),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name="Document",
+            fields=[
+                (
+                    "id",
+                    models.BigAutoField(
+                        auto_created=True,
+                        primary_key=True,
+                        serialize=False,
+                        verbose_name="ID",
+                    ),
+                ),
+                (
+                    "number",
+                    models.CharField(
+                        blank=True, db_index=True, max_length=255, null=True
+                    ),
+                ),
+                ("position", models.PositiveIntegerField(null=True)),
+                ("date", models.DateField()),
+                (
+                    "counter",
+                    models.ForeignKey(
+                        null=True,
+                        on_delete=django.db.models.deletion.PROTECT,
+                        to="enumeration.counter",
+                    ),
+                ),
+                (
+                    "sequence",
+                    models.ForeignKey(
+                        null=True,
+                        on_delete=django.db.models.deletion.PROTECT,
+                        to="enumeration.sequence",
+                    ),
+                ),
+            ],
+            options={
+                "abstract": False,
+            },
+        ),
+    ]
diff --git a/src/enumeration/tests/migrations/__init__.py b/src/enumeration/tests/migrations/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/src/enumeration/tests/models.py b/src/enumeration/tests/models.py
new file mode 100644
index 0000000..4df7be4
--- /dev/null
+++ b/src/enumeration/tests/models.py
@@ -0,0 +1,9 @@
+from django.db import models
+from enumeration.mixins import EnumeratedModelMixin
+
+
+class Document(EnumeratedModelMixin):
+    date = models.DateField()
+
+    def get_enumeration_context(self):
+        return {"date": self.date}
diff --git a/test/settings.py b/src/enumeration/tests/settings.py
similarity index 94%
rename from test/settings.py
rename to src/enumeration/tests/settings.py
index 82d815d..eb7e444 100644
--- a/test/settings.py
+++ b/src/enumeration/tests/settings.py
@@ -1,5 +1,3 @@
-DATABASE_ENGINE = "sqlite3"
-
 DATABASES = {
     "default": {
         "ENGINE": "django.db.backends.postgresql",
@@ -17,6 +15,7 @@
     # 'django.contrib.auth',
     # 'django.contrib.admin',
     "enumeration",
+    "enumeration.tests",
 ]
 
 SECRET_KEY = "enumeration"
diff --git a/test/test_consume_gap.py b/src/enumeration/tests/test_consume_gap.py
similarity index 100%
rename from test/test_consume_gap.py
rename to src/enumeration/tests/test_consume_gap.py
diff --git a/test/test_format.py b/src/enumeration/tests/test_format.py
similarity index 100%
rename from test/test_format.py
rename to src/enumeration/tests/test_format.py
diff --git a/test/test_format_validator.py b/src/enumeration/tests/test_format_validator.py
similarity index 100%
rename from test/test_format_validator.py
rename to src/enumeration/tests/test_format_validator.py
diff --git a/test/test_get_next.py b/src/enumeration/tests/test_get_next.py
similarity index 100%
rename from test/test_get_next.py
rename to src/enumeration/tests/test_get_next.py
diff --git a/test/test_get_number.py b/src/enumeration/tests/test_get_number.py
similarity index 100%
rename from test/test_get_number.py
rename to src/enumeration/tests/test_get_number.py
diff --git a/test/test_increment.py b/src/enumeration/tests/test_increment.py
similarity index 100%
rename from test/test_increment.py
rename to src/enumeration/tests/test_increment.py
diff --git a/test/test_misc.py b/src/enumeration/tests/test_misc.py
similarity index 100%
rename from test/test_misc.py
rename to src/enumeration/tests/test_misc.py
diff --git a/src/enumeration/tests/test_model_mixin.py b/src/enumeration/tests/test_model_mixin.py
new file mode 100644
index 0000000..4d51ed1
--- /dev/null
+++ b/src/enumeration/tests/test_model_mixin.py
@@ -0,0 +1,62 @@
+import pytest
+from datetime import date
+from enumeration.models import Sequence, ResetPeriod, Counter
+from .models import Document
+
+
+@pytest.fixture()
+def sequence(db):
+    return Sequence.objects.create(format="YYMM###", reset_period=ResetPeriod.MONTHLY)
+
+
+def test_assign_number(sequence):
+    d = Document(sequence=sequence, date=date(2024, 11, 5))
+    d.assign_number()
+    assert d.number == "2411001"
+    assert d.position == 1
+    assert d.counter == Counter.objects.get(
+        sequence=sequence, position=1, period=date(2024, 11, 1)
+    )
+
+    # can't assign
+    with pytest.raises(RuntimeError):
+        d.assign_number()
+
+
+def test_reassing(sequence):
+
+    i = Document(sequence=sequence, date=date(2024, 11, 5))
+    i.assign_number()
+
+    assert i.number == "2411001"
+    assert i.position == 1
+    assert i.counter == Counter.objects.get(
+        sequence=sequence, position=1, period=date(2024, 11, 1)
+    )
+
+    # jump day in same month
+    i.date = date(2024, 11, 2)
+    i.reassign_number()
+
+    assert i.number == "2411001"
+    assert i.position == 1
+    assert i.counter == Counter.objects.get(
+        sequence=sequence, position=1, period=date(2024, 11, 1)
+    )
+
+    # move to next month
+    i.date = date(2024, 12, 2)
+    i.reassign_number()
+    assert i.number == "2412001"
+    assert i.position == 1
+    assert i.counter == Counter.objects.get(
+        sequence=sequence, position=1, period=date(2024, 12, 1)
+    )
+
+    i = Document(sequence=sequence, date=date(2024, 12, 1))
+    i.assign_number()
+    assert i.number == "2412002"
+    assert i.position == 2
+    assert i.counter == Counter.objects.get(
+        sequence=sequence, position=2, period=date(2024, 12, 1)
+    )