server/AyaNova/biz/PartAssemblyBiz.cs

@@ -272,6 +272,12 @@ namespace AyaNova.Biz
                 }
             }
 
+            //no duplicate parts
+            //this would be caused by an API user not our UI so no need to translation
+            if (proposedObj.Items.GroupBy(z => z.PartId).Any(g => g.Count() > 1))
+            {
+                AddError(ApiErrorCode.VALIDATION_FAILED, "Items", "Duplicate parts are not allowed in the items collection");
+            }
 
             //Any form customizations to validate?
             var FormCustomization = await ct.FormCustom.AsNoTracking().SingleOrDefaultAsync(x => x.FormKey == AyaType.PartAssembly.ToString());