Tree query improvements (#3443)

* Allow part category table to be ordered by part count

* Add queryset annotation for part-category part-count

- Uses subquery to annotate the part-count for sub-categories
- Huge reduction in number of queries

* Update 'pathstring' property of PartCategory and StockLocation

- No longer a dynamically calculated value
- Constructed when the model is saved, and then written to the database
- Limited to 250 characters

* Data migration to re-construct pathstring for PartCategory objects

* Fix for tree model save() method

* Add unit tests for pathstring construction

* Data migration for StockLocation pathstring values

* Update part API

- Add new annotation to PartLocationDetail view

* Update API version

* Apply similar annotation to StockLocation API endpoints

* Extra tests for PartCategory API

* Unit test fixes

* Allow PartCategory and StockLocation lists to be sorted by 'pathstring'

* Further unit test fixes

InvenTree/templates/js/translated/part.js

@@ -1778,6 +1778,7 @@ function loadPartCategoryTable(table, options) {
         name: 'category',
         original: original,
         showColumns: true,
+        sortable: true,
         buttons: options.allowTreeView ? [
             {
                 icon: 'fas fa-bars',
@@ -1882,13 +1883,13 @@ function loadPartCategoryTable(table, options) {
                 title: '{% trans "Path" %}',
                 switchable: !tree_view,
                 visible: !tree_view,
-                sortable: false,
+                sortable: true,
             },
             {
-                field: 'parts',
+                field: 'part_count',
                 title: '{% trans "Parts" %}',
                 switchable: true,
-                sortable: false,
+                sortable: true,
             }
         ]
     });

InvenTree/templates/js/translated/stock.js

@@ -2264,6 +2264,7 @@ function loadStockLocationTable(table, options) {
         queryParams: filters,
         name: 'location',
         original: original,
+        sortable: true,
         showColumns: true,
         onPostBody: function() {
 
@@ -2360,14 +2361,13 @@ function loadStockLocationTable(table, options) {
                 field: 'pathstring',
                 title: '{% trans "Path" %}',
                 switchable: true,
-                sortable: false,
+                sortable: true,
             },
             {
                 field: 'items',
                 title: '{% trans "Stock Items" %}',
                 switchable: true,
-                sortable: false,
-                sortName: 'item_count',
+                sortable: true,
             }
         ]
     });