Change item quantity field from PositiveInteger to Decimal

- Allow 'partial' quantity e.g. '0.45kg'
- Need to change some maths functions as Decimal type is pernickity

InvenTree/part/migrations/0024_auto_20191118_2139.py

@@ -0,0 +1,19 @@
+# Generated by Django 2.2.5 on 2019-11-18 21:39
+
+import django.core.validators
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('part', '0023_auto_20190913_1401'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='bomitem',
+            name='quantity',
+            field=models.DecimalField(decimal_places=5, default=1.0, help_text='BOM quantity for this BOM item', max_digits=15, validators=[django.core.validators.MinValueValidator(0)]),
+        ),
+    ]

InvenTree/part/models.py

@@ -517,7 +517,7 @@ class Part(models.Model):
         # Calculate the minimum number of parts that can be built using each sub-part
         for item in self.bom_items.all().prefetch_related('sub_part__stock_items'):
             stock = item.sub_part.available_stock
-            n = int(1.0 * stock / item.quantity)
+            n = int(stock / item.quantity)
 
             if total is None or n < total:
                 total = n
@@ -1064,7 +1064,7 @@ class BomItem(models.Model):
                                  })
 
     # Quantity required
-    quantity = models.PositiveIntegerField(default=1, validators=[MinValueValidator(0)], help_text='BOM quantity for this BOM item')
+    quantity = models.DecimalField(default=1.0, max_digits=15, decimal_places=5, validators=[MinValueValidator(0)], help_text=_('BOM quantity for this BOM item'))
 
     overage = models.CharField(max_length=24, blank=True, validators=[validators.validate_overage],
                                help_text=_('Estimated build wastage quantity (absolute or percentage)')

InvenTree/stock/migrations/0016_auto_20191118_2146.py

@@ -0,0 +1,19 @@
+# Generated by Django 2.2.5 on 2019-11-18 21:46
+
+import django.core.validators
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('stock', '0015_auto_20190913_1407'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='stockitem',
+            name='quantity',
+            field=models.DecimalField(decimal_places=5, default=1, max_digits=15, validators=[django.core.validators.MinValueValidator(0)]),
+        ),
+    ]

InvenTree/stock/models.py

@@ -323,7 +323,7 @@ class StockItem(models.Model):
     batch = models.CharField(max_length=100, blank=True, null=True,
                              help_text=_('Batch code for this stock item'))
 
-    quantity = models.PositiveIntegerField(validators=[MinValueValidator(0)], default=1)
+    quantity = models.DecimalField(max_digits=15, decimal_places=5, validators=[MinValueValidator(0)], default=1)
 
     updated = models.DateField(auto_now=True, null=True)