don't use search filter instance since it's not properly supported yet

Author: lekoala

_config/softdelete.yml

@@ -13,12 +13,18 @@ SilverStripe\Admin\SecurityAdmin:
     - SoftDeleteSecurityAdmin
 ---
 Name: softdelete-searchfilters
-After: '#coresearchfilters'
+After: "#coresearchfilters"
 ---
 SilverStripe\Core\Injector\Injector:
   DataListFilter.SoftDelete:
     class: SoftDeleteSearchFilter
   DataListFilter.SoftDeleteSearch:
     class: SoftDeleteSearchFilter
-  SoftDeleteSearchFilter: '%$DataListFilter.SoftDelete'
-  SoftDeleteSearch: '%$DataListFilter.SoftDelete'
+  DataListFilter.SoftDeleteOnly:
+    class: SoftDeleteOnlySearchFilter
+  DataListFilter.SoftDeleteOnlySearch:
+    class: SoftDeleteOnlySearchFilter
+  SoftDeleteSearchFilter: "%$DataListFilter.SoftDelete"
+  SoftDeleteSearch: "%$DataListFilter.SoftDelete"
+  SoftDeleteOnlySearchFilter: "%$DataListFilter.SoftDeleteOnly"
+  SoftDeleteOnlySearch: "%$DataListFilter.SoftDeleteOnly"

code/SoftDeletable.php

@@ -76,13 +76,12 @@ public function updateSearchableFields(array &$fields)
   ...
         */
         $fields['IncludeDeleted'] = [
-            'filter' => 'SoftDeleteSearchFilter',
+            'filter' => SoftDeleteSearchFilter::class,
             'field' => CheckboxField::class,
             'title' => 'Include deleted',
         ];
-        // Can can declare search filters instance directly with our modifier
         $fields['OnlyDeleted'] = [
-            'filter' => new SoftDeleteSearchFilter('Deleted', 1, ['only']),
+            'filter' => SoftDeleteOnlySearchFilter::class,
             'field' => CheckboxField::class,
             'title' => 'Only deleted',
         ];

code/SoftDeleteOnlySearchFilter.php

@@ -0,0 +1,20 @@
+<?php
+
+/**
+ * Filters or not soft deleted record using the filter api
+ */
+class SoftDeleteOnlySearchFilter extends SoftDeleteSearchFilter
+{
+    public function getSupportedModifiers()
+    {
+        return [];
+    }
+
+    /**
+     * @return bool
+     */
+    protected function getOnlyDeleted()
+    {
+        return true;
+    }
+}