declare primary keys on all models

app/Container.php

@@ -17,6 +17,9 @@ class Container extends Model
         'cid', 'name'
     ];
 
+
+    protected $primaryKey = 'cid';
+
     /**
      * The attributes excluded from the model's JSON form.
      *

app/Event.php

@@ -16,6 +16,8 @@ class Event extends Model
         'eid', 'name', 'slug', 'start', 'end', 'pre_start', 'post_end'
     ];
 
+
+    protected $primaryKey = 'eid';
     /**
      * The attributes excluded from the model's JSON form.
      *

app/Item.php

@@ -18,6 +18,9 @@ class Item extends Model
         'iid', 'item_uid', 'bezeichnung', 'wann', 'wo', 'eid', 'cid'
     ];
 
+
+    protected $primaryKey = 'iid';
+
     /**
      * The attributes excluded from the model's JSON form.
      *