Adds metadata mixin class for adding JSON field to internal tables

- Add metadata field to stocklocation
- Add metadata field to stockitem

InvenTree/plugin/models.py

@@ -16,6 +16,30 @@ import common.models
 from plugin import InvenTreePlugin, registry
 
 
+class MetadataMixin(models.Model):
+    """
+    Model mixin class which adds a JSON metadata field to a model,
+    for use by any (and all) plugins.
+
+    The intent of this mixin is to provide a metadata field on a model instance,
+    for plugins to read / modify as required, to store any extra information.
+    
+    The assumptions for models implementing this mixin are:
+
+    - The internal InvenTree business logic will make no use of this field
+    - Multiple plugins may read / write to this metadata field, and not assume they have sole rights 
+    """
+
+    class Meta:
+        abstract = True
+
+    metadata = models.JSONField(
+        blank=True, null=True,
+        verbose_name=_('Plugin Metadata'),
+        help_text=_('JSON metadata field, for use by external plugins'),
+    )
+
+
 class PluginConfig(models.Model):
     """
     A PluginConfig object holds settings for plugins.

InvenTree/stock/migrations/0075_auto_20220515_1440.py

@@ -0,0 +1,27 @@
+# Generated by Django 3.2.13 on 2022-05-15 14:40
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('stock', '0074_alter_stockitem_batch'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='stockitem',
+            name='metadata',
+            field=models.JSONField(blank=True, help_text='JSON metadata field, for use by external plugins', null=True, verbose_name='Plugin Metadata'),
+        ),
+        migrations.AddField(
+            model_name='stocklocation',
+            name='metadata',
+            field=models.JSONField(blank=True, help_text='JSON metadata field, for use by external plugins', null=True, verbose_name='Plugin Metadata'),
+        ),
+        migrations.AlterUniqueTogether(
+            name='stocklocation',
+            unique_together=set(),
+        ),
+    ]

InvenTree/stock/models.py

@@ -38,6 +38,7 @@ import common.models
 import report.models
 import label.models
 
+from plugin.models import MetadataMixin
 from plugin.events import trigger_event
 
 from InvenTree.status_codes import StockStatus, StockHistoryCode
@@ -51,7 +52,7 @@ from company import models as CompanyModels
 from part import models as PartModels
 
 
-class StockLocation(InvenTreeTree):
+class StockLocation(MetadataMixin, InvenTreeTree):
     """ Organization tree for StockItem objects
     A "StockLocation" can be considered a warehouse, or storage location
     Stock locations can be heirarchical as required
@@ -242,7 +243,7 @@ def generate_batch_code():
     return Template(batch_template).render(context)
 
 
-class StockItem(MPTTModel):
+class StockItem(MetadataMixin, MPTTModel):
     """
     A StockItem object represents a quantity of physical instances of a part.