Update definition for StockItemAllocation model

- Limit foreignkey choices
- Error checking
- Check if a StockItem is over-allocated
- Fix API serialization and filtering

InvenTree/order/migrations/0025_auto_20200422_0222.py

@@ -0,0 +1,18 @@
+# Generated by Django 3.0.5 on 2020-04-22 02:22
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('stock', '0031_auto_20200422_0209'),
+        ('order', '0024_salesorderallocation'),
+    ]
+
+    operations = [
+        migrations.AlterUniqueTogether(
+            name='salesorderallocation',
+            unique_together={('line', 'item')},
+        ),
+    ]

InvenTree/order/migrations/0026_auto_20200422_0224.py

@@ -0,0 +1,20 @@
+# Generated by Django 3.0.5 on 2020-04-22 02:24
+
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('stock', '0031_auto_20200422_0209'),
+        ('order', '0025_auto_20200422_0222'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='salesorderallocation',
+            name='item',
+            field=models.OneToOneField(limit_choices_to={'part__salable': True}, on_delete=django.db.models.deletion.CASCADE, related_name='sales_order_allocation', to='stock.StockItem'),
+        ),
+    ]

InvenTree/order/migrations/0027_auto_20200422_0236.py

@@ -0,0 +1,20 @@
+# Generated by Django 3.0.5 on 2020-04-22 02:36
+
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('stock', '0031_auto_20200422_0209'),
+        ('order', '0026_auto_20200422_0224'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='salesorderallocation',
+            name='item',
+            field=models.ForeignKey(limit_choices_to={'part__salable': True}, on_delete=django.db.models.deletion.CASCADE, related_name='sales_order_allocations', to='stock.StockItem'),
+        ),
+    ]