Add "Reference" field to Build model

InvenTree/build/migrations/0018_build_reference.py

@@ -0,0 +1,64 @@
+# Generated by Django 3.0.7 on 2020-10-19 11:25
+
+from django.db import migrations, models
+
+
+def add_default_reference(apps, schema_editor):
+    """
+    Add a "default" build-order reference for any existing build orders.
+    Best we can do is use the PK of the build order itself.
+    """
+
+    Build = apps.get_model('build', 'Build')
+
+    count = 0
+
+    for build in Build.objects.all():
+
+        build.reference = str(build.pk)
+        build.save()
+        count += 1
+
+    print(f"\nUpdated build reference for {count} existing BuildOrder objects")
+
+
+def reverse_default_reference(apps, schema_editor):
+    """
+    Do nothing! But we need to have a function here so the whole process is reversible.
+    """
+    pass
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('build', '0017_auto_20200426_0612'),
+    ]
+
+    operations = [
+        # Initial operation - create a 'reference' field for the Build object:
+        migrations.AddField(
+            model_name='build',
+            name='reference',
+            field=models.CharField(help_text='Build Order Reference', blank=True, max_length=64, unique=False, verbose_name='Reference'),
+        ),
+
+        # Auto-populate the new reference field for any existing build order objects
+        migrations.RunPython(
+            add_default_reference,
+            reverse_code=reverse_default_reference
+        ),
+
+        # Now that each build has a non-empty, unique reference, update the field requirements!
+        migrations.AlterField(
+            model_name='build',
+            name='reference',
+            field=models.CharField(
+                help_text='Build Order Reference',
+                max_length=64,
+                blank=False,
+                unique=True,
+                verbose_name='Reference'
+            )
+        )
+    ]

InvenTree/build/models.py

@@ -34,6 +34,7 @@ class Build(MPTTModel):
 
     Attributes:
         part: The part to be built (from component BOM items)
+        reference: Build order reference (required, must be unique)
         title: Brief title describing the build (required)
         quantity: Number of units to be built
         parent: Reference to a Build object for which this Build is required
@@ -69,6 +70,14 @@ class Build(MPTTModel):
         except PartModels.Part.DoesNotExist:
             pass
 
+    reference = models.CharField(
+        unique=True,
+        max_length=64,
+        blank=False,
+        help_text=_('Build Order Reference'),
+        verbose_name=_('Reference'),
+    )
+
     title = models.CharField(
         verbose_name=_('Build Title'),
         blank=False,