feat(products): add support for product sales units

Add new models UnitOfMeasure and ProductSalesUnit to enable selling products in different units (e.g., bunches, kg). Update Product model with base_unit field and methods for unit conversions and availability. Extend Sale, Reservation, and OrderItem models with sales_unit fields and snapshots. Modify SaleProcessor to handle quantity conversions. Include admin interfaces for managing units. Add corresponding database migrations.

myproject/orders/migrations/0003_add_sales_unit_fields.py

@@ -0,0 +1,55 @@
+# Generated by Django 5.0.10 on 2026-01-01 21:29
+
+import django.db.models.deletion
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('orders', '0002_initial'),
+        ('products', '0006_populate_unit_of_measure'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='historicalorderitem',
+            name='conversion_factor_snapshot',
+            field=models.DecimalField(blank=True, decimal_places=6, help_text='Коэффициент конверсии на момент заказа', max_digits=15, null=True, verbose_name='Коэффициент конверсии (snapshot)'),
+        ),
+        migrations.AddField(
+            model_name='historicalorderitem',
+            name='quantity_in_base_units',
+            field=models.DecimalField(blank=True, decimal_places=6, help_text='Количество в единицах хранения товара (для списания со склада)', max_digits=10, null=True, verbose_name='Количество в базовых единицах'),
+        ),
+        migrations.AddField(
+            model_name='historicalorderitem',
+            name='sales_unit',
+            field=models.ForeignKey(blank=True, db_constraint=False, null=True, on_delete=django.db.models.deletion.DO_NOTHING, related_name='+', to='products.productsalesunit', verbose_name='Единица продажи'),
+        ),
+        migrations.AddField(
+            model_name='historicalorderitem',
+            name='unit_name_snapshot',
+            field=models.CharField(blank=True, default='', help_text='Название единицы продажи на момент заказа', max_length=100, verbose_name='Название единицы (snapshot)'),
+        ),
+        migrations.AddField(
+            model_name='orderitem',
+            name='conversion_factor_snapshot',
+            field=models.DecimalField(blank=True, decimal_places=6, help_text='Коэффициент конверсии на момент заказа', max_digits=15, null=True, verbose_name='Коэффициент конверсии (snapshot)'),
+        ),
+        migrations.AddField(
+            model_name='orderitem',
+            name='quantity_in_base_units',
+            field=models.DecimalField(blank=True, decimal_places=6, help_text='Количество в единицах хранения товара (для списания со склада)', max_digits=10, null=True, verbose_name='Количество в базовых единицах'),
+        ),
+        migrations.AddField(
+            model_name='orderitem',
+            name='sales_unit',
+            field=models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.SET_NULL, related_name='order_items', to='products.productsalesunit', verbose_name='Единица продажи'),
+        ),
+        migrations.AddField(
+            model_name='orderitem',
+            name='unit_name_snapshot',
+            field=models.CharField(blank=True, default='', help_text='Название единицы продажи на момент заказа', max_length=100, verbose_name='Название единицы (snapshot)'),
+        ),
+    ]