Fix error on delete of matchgrid row (CO-2125)

app/src/Controller/AppController.php

@@ -192,6 +192,12 @@ protected function getPrimaryLink(bool $lookup=false) {
             $this->cur_pl['linkvalue'] = $this->request->getData($this->cur_pl['linkattr']);
           } elseif(!empty($this->request->getData($modelName . "." . $this->cur_pl['linkattr']))) {
             $this->cur_pl['linkvalue'] = $this->request->getData($modelName . "." . $this->cur_pl['linkattr']);
+          } elseif($this->$modelsName->allowUnkeyedPrimaryLink($this->request->getParam('action'))
+             && $this->request->getQuery($this->cur_pl['linkattr'])) {
+            // If this action allows unkeyed, asserted primary link IDs, check the query
+            // string (eg: 'add' or 'index' allow matchgrid_id to be passed in). Note we
+            // do this even though we're in post/put.
+            $this->cur_pl['linkvalue'] = $this->request->getQuery($this->cur_pl['linkattr']);
           } elseif($this->$modelsName->allowLookupPrimaryLink($this->request->getParam('action'))) {
             // Try to map the requested object ID (this is probably a delete, so no attribute in post body)
             $param = (int)$this->request->getParam('pass.0');
@@ -265,6 +271,12 @@ protected function setMatchgrid() {
             $mgid = $this->request->getData('matchgrid_id');
           } elseif(!empty($this->request->getData($modelName . ".matchgrid_id"))) {
             $mgid = $this->request->getData($modelName . ".matchgrid_id");
+          } elseif($this->name == 'MatchgridRecords'
+                   && !empty($this->request->getQuery('matchgrid_id'))) {
+            // As a special case for MatchgridRecords, we accept the matchgrid_id
+            // as a get parameter even though the action is post/put, since this
+            // is how it is provided for a delete action.
+            $mgid = $this->request->getQuery('matchgrid_id');
           }
         }
       } else {