Add choice fields

README.rst

@@ -33,10 +33,15 @@ model like so:
 .. code:: python
 
     from django.db import models
+    from dateutil.relativedelta import relativedelta
     from relativedeltafield import RelativeDeltaField
 
     class MyModel(models.Model):
-      rdfield=RelativeDeltaField()
+        rdfield = RelativeDeltaField()
+        rdchoices = RelativeDeltaField(choices=[
+            ('P1M', '1 month'),
+            (relativedelta(months=2), '2 month'),
+        ])
 
 Then later, you can use it:
 
@@ -78,6 +83,10 @@ app to always force ``full_clean()`` on ``save()``, so you can be
 sure that after a ``save()``, your fields are both normalized
 and validated.
 
+You can use `relativedeltafield.forms.RelativeDeltaChoiceField` to update
+`RelativeDeltaField` using a `Select` widget. If you provide `choices` argument
+to `RelativeDeltaField`, then `ModelForm` and `admin` will automatically use
+`RelativeDeltaChoiceField`.
 
 Limitations and pitfalls
 ------------------------

src/relativedeltafield/__init__.py

@@ -1,12 +1,26 @@
 import re
+from datetime import timedelta
 
-import django
+import relativedeltafield.forms
+from dateutil.relativedelta import relativedelta
 from django.core.exceptions import ValidationError
 from django.db import models
 from django.utils.translation import ugettext_lazy as _
 
-from datetime import timedelta
-from dateutil.relativedelta import relativedelta
+
+try:
+	from django.db.migrations.serializer import BaseSerializer
+	from django.db.migrations.writer import MigrationWriter
+	has_migration_serializer = True
+except ImportError:
+	has_migration_serializer = False
+
+try:
+	from django.utils.deconstruct import deconstructible
+	has_migration_deconstructible = True
+except ImportError:
+	has_migration_deconstructible = False
+
 
 __version__ = '1.1.2'
 
@@ -90,6 +104,14 @@ class RelativeDeltaField(models.Field):
 	}
 	description = _("RelativeDelta")
 
+	def __init__(self, *args, **kwargs):
+		if 'choices' in kwargs:
+			kwargs['choices'] = [
+				(self.to_python(value), label)
+				for value, label in
+				kwargs['choices']
+			]
+		super().__init__(*args, **kwargs)
 
 	def db_type(self, connection):
 		if connection.vendor == 'postgresql':
@@ -147,3 +169,20 @@ def from_db_value(self, value, expression, connection, context=None):
 	def value_to_string(self, obj):
 		val = self.value_from_object(obj)
 		return '' if val is None else format_relativedelta(val)
+
+	def formfield(self, *args, **kwargs):
+		kwargs.setdefault('choices_form_class', relativedeltafield.forms.RelativeDeltaChoiceField)
+		return super().formfield(*args, **kwargs)
+
+
+if has_migration_serializer:
+	# Django 2.2 and up
+	class RelativeDeltaSerializer(BaseSerializer):
+		def serialize(self):
+			return repr(self.value), {'from dateutil.relativedelta import relativedelta'}
+
+	MigrationWriter.register_serializer(relativedelta, RelativeDeltaSerializer)
+
+elif has_migration_deconstructible:
+	# Django 2.1 and lower
+	deconstructible(relativedelta)

src/relativedeltafield/forms.py

@@ -0,0 +1,24 @@
+import relativedeltafield
+from dateutil.relativedelta import relativedelta
+from django import forms
+
+
+class RelativeDeltaChoiceField(forms.TypedChoiceField):
+	def _set_choices(self, value):
+		value = [(self.prepare_value(val), label) for val, label in value]
+		super()._set_choices(value)
+	choices = property(forms.TypedChoiceField._get_choices, _set_choices)
+
+	def to_python(self, value):
+		if value in self.empty_values:
+			return None
+		return relativedeltafield.parse_relativedelta(value)
+
+	def prepare_value(self, value):
+		if isinstance(value, relativedelta):
+			return relativedeltafield.format_relativedelta(value)
+		return super().prepare_value(value)
+
+	def valid_value(self, value):
+		value = self.prepare_value(value)
+		return super().valid_value(value)

tests/test_forms.py

@@ -0,0 +1,72 @@
+from dateutil.relativedelta import relativedelta
+from django import forms
+from django.test import TestCase
+from testapp.models import Interval, IntervalWithChoice
+
+IntervalForm = forms.modelform_factory(model=IntervalWithChoice, fields=forms.ALL_FIELDS)
+
+
+class RelativeDeltaFormFieldTest(TestCase):
+	def setUp(self):
+		self.obj = Interval.objects.create(value=relativedelta(years=1))
+
+	def test_unbound_form_rendering(self):
+		form = IntervalForm()
+
+		self.assertHTMLEqual(
+			str(form['value']),
+			'''
+				<select name="value" id="id_value">
+					<option value="" selected>---------</option>
+					<option value="P1M">1 month</option>
+					<option value="P3M">3 months</option>
+					<option value="P6M">6 months</option>
+				</select>
+			'''
+		)
+
+	def test_bound_form_rendering(self):
+		self.obj = Interval.objects.create(value=relativedelta(months=3))
+		form = IntervalForm(instance=self.obj)
+
+		self.assertHTMLEqual(
+			str(form['value']),
+			'''
+				<select name="value" id="id_value">
+					<option value="">---------</option>
+					<option value="P1M">1 month</option>
+					<option selected value="P3M">3 months</option>
+					<option value="P6M">6 months</option>
+				</select>
+			'''
+		)
+
+	def test_form_submission_string_choice(self):
+		self.obj = IntervalWithChoice.objects.create(value=relativedelta(months=1))
+		data = {'value': 'P3M'}
+		form = IntervalForm(data, instance=self.obj)
+		self.assertTrue(form.is_valid())
+		form.save()
+
+		self.obj.refresh_from_db()
+		self.assertEqual(self.obj.value, relativedelta(months=3))
+
+	def test_form_submission_relativedelta_choice(self):
+		self.obj = IntervalWithChoice.objects.create(value=relativedelta(months=1))
+		data = {'value': 'P6M'}
+		form = IntervalForm(data, instance=self.obj)
+		self.assertTrue(form.is_valid())
+		form.save()
+
+		self.obj.refresh_from_db()
+		self.assertEqual(self.obj.value, relativedelta(months=6))
+
+	def test_form_submission_empty(self):
+		self.obj = IntervalWithChoice.objects.create(value=relativedelta(months=1))
+		data = {'value': ''}
+		form = IntervalForm(data, instance=self.obj)
+		self.assertTrue(form.is_valid())
+		form.save()
+
+		self.obj.refresh_from_db()
+		self.assertIsNone(self.obj.value)

tests/testproject/testapp/migrations/0001_initial.py

@@ -0,0 +1,22 @@
+# Generated by Django 3.1.1 on 2020-09-28 19:01
+
+import relativedeltafield
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    initial = True
+
+    dependencies = [
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='Interval',
+            fields=[
+                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('value', relativedeltafield.RelativeDeltaField(blank=True, null=True)),
+            ],
+        ),
+    ]

tests/testproject/testapp/migrations/0002_intervalwithchoice.py

@@ -0,0 +1,22 @@
+# Generated by Django 3.1.1 on 2020-09-28 22:05
+
+from dateutil.relativedelta import relativedelta
+from django.db import migrations, models
+import relativedeltafield
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('testapp', '0001_initial'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='IntervalWithChoice',
+            fields=[
+                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('value', relativedeltafield.RelativeDeltaField(blank=True, choices=[(relativedelta(months=+1), '1 month'), (relativedelta(months=+3), '3 months'), (relativedelta(months=+6), '6 months')], null=True)),
+            ],
+        ),
+    ]

tests/testproject/testapp/models.py

@@ -1,5 +1,16 @@
+from dateutil.relativedelta import relativedelta
 from django.db import models
 from relativedeltafield import RelativeDeltaField
 
+
 class Interval(models.Model):
 	value=RelativeDeltaField(null=True, blank=True)
+
+
+class IntervalWithChoice(models.Model):
+	CHOICES = [
+		(relativedelta(months=1), '1 month'),
+		('P3M', '3 months'),
+		(relativedelta(months=6), '6 months'),
+	]
+	value=RelativeDeltaField(null=True, blank=True, choices=CHOICES)

tests/testproject/testproject/admin.py

@@ -1,8 +1,15 @@
 from django.contrib import admin
 
-from testapp.models import Interval
+from testapp.models import Interval, IntervalWithChoice
+
 
 @admin.register(Interval)
 class IntervalAdmin(admin.ModelAdmin):
 	list_display = ['value']
 	list_filter = ['value']
+
+
+@admin.register(IntervalWithChoice)
+class IntervalWithChoiceAdmin(admin.ModelAdmin):
+	list_display = ['value']
+	list_filter = ['value']