Part page loading improvements (#3185)

* Lazy load the pricing bom table when the "pricing" tab is selected

* Update django-debug-toolbar configuration

* Major refactoring for the 'can_build' function

- Use a single annotated query to the db, rather than a for loop (which is what a caveman would use)
- Query performance is greatly improved
- Also refactors existing variant-part-stock subquery code, to make it re-usable

* Use minified JS and CSS where possible

* Render a 'preview' version of each part image

- Saves load time when the image is quite large
- Adds a data migration to render out the new variation

* Adds 'preview' version of company images

* Defer loading of javascript files

Note: some cannot be deferred - jquery in particular

* Crucial bugfix for user roles context

- Previously was *not* being calculated correctly
- A non-superuser role would most likely display pages incorrectly

* Prevent loading of "about" on every page

- Load dynamically when requested
- Takes ~400ms!
- Cuts out a lot of fat

* Match displayed image size to preview image size

* Utilize caching framework for accessing user "role" information

- Reduces number of DB queries required by rendering framework

* Remove redundant query elements

* Remove 'stock' field from PartBrief serializer

- A calculated field on a serializer is a *bad idea* when that calculation requires a DB hit

* Query improvements for StockItem serializer

- Remove calculated fields
- Fix annotations

* Bug fixes

* Remove JS load test

- Loading of JS files is now deferred, so the unit test does not work as it used to

* Fix broken template for "maintenance" page

* Remove thumbnail generation migrations

- Already performed manually as part of ''invoke migrate"
- Running as a migration causes unit test problems
- Not sensible to run this as a data-migration anyway

* tweak for build table

InvenTree/part/serializers.py

@@ -4,8 +4,7 @@ import imghdr
 from decimal import Decimal
 
 from django.db import models, transaction
-from django.db.models import (ExpressionWrapper, F, FloatField, Func, Q,
-                              Subquery)
+from django.db.models import ExpressionWrapper, F, FloatField, Q
 from django.db.models.functions import Coalesce
 from django.urls import reverse_lazy
 from django.utils.translation import gettext_lazy as _
@@ -251,8 +250,6 @@ class PartBriefSerializer(InvenTreeModelSerializer):
 
     thumbnail = serializers.CharField(source='get_thumbnail_url', read_only=True)
 
-    stock = serializers.FloatField(source='total_stock')
-
     class Meta:
         """Metaclass defining serializer fields"""
         model = Part
@@ -270,7 +267,6 @@ class PartBriefSerializer(InvenTreeModelSerializer):
             'is_template',
             'purchaseable',
             'salable',
-            'stock',
             'trackable',
             'virtual',
             'units',
@@ -322,14 +318,7 @@ class PartSerializer(InvenTreeModelSerializer):
         variant_query = part.filters.variant_stock_query()
 
         queryset = queryset.annotate(
-            variant_stock=Coalesce(
-                Subquery(
-                    variant_query.annotate(
-                        total=Func(F('quantity'), function='SUM', output_field=FloatField())
-                    ).values('total')),
-                0,
-                output_field=FloatField(),
-            )
+            variant_stock=part.filters.annotate_variant_quantity(variant_query, reference='quantity'),
         )
 
         # Filter to limit builds to "active"
@@ -642,35 +631,14 @@ class BomItemSerializer(InvenTreeModelSerializer):
         variant_stock_query = part.filters.variant_stock_query(reference='sub_part__')
 
         queryset = queryset.alias(
-            variant_stock_total=Coalesce(
-                Subquery(
-                    variant_stock_query.annotate(
-                        total=Func(F('quantity'), function='SUM', output_field=FloatField())
-                    ).values('total')),
-                0,
-                output_field=FloatField()
-            ),
-            variant_stock_build_order_allocations=Coalesce(
-                Subquery(
-                    variant_stock_query.annotate(
-                        total=Func(F('sales_order_allocations__quantity'), function='SUM', output_field=FloatField()),
-                    ).values('total')),
-                0,
-                output_field=FloatField(),
-            ),
-            variant_stock_sales_order_allocations=Coalesce(
-                Subquery(
-                    variant_stock_query.annotate(
-                        total=Func(F('allocations__quantity'), function='SUM', output_field=FloatField()),
-                    ).values('total')),
-                0,
-                output_field=FloatField(),
-            )
+            variant_stock_total=part.filters.annotate_variant_quantity(variant_stock_query, reference='quantity'),
+            variant_bo_allocations=part.filters.annotate_variant_quantity(variant_stock_query, reference='sales_order_allocations__quantity'),
+            variant_so_allocations=part.filters.annotate_variant_quantity(variant_stock_query, reference='allocations__quantity'),
         )
 
         queryset = queryset.annotate(
             available_variant_stock=ExpressionWrapper(
-                F('variant_stock_total') - F('variant_stock_build_order_allocations') - F('variant_stock_sales_order_allocations'),
+                F('variant_stock_total') - F('variant_bo_allocations') - F('variant_so_allocations'),
                 output_field=FloatField(),
             )
         )