Getting Error: System.TypeException: Invalid conversion from runtime type List<ANY> to Map<String,ANY>

Question

I'm getting error in the following apex method: System.TypeException: Invalid conversion from runtime type List to Map<String,ANY>

Please find the apex method:

@AuraEnabled(cacheable=true)  
    public static void updateQuantity(String recordId, Object quantity){
        System.debug('recordId--------->' + recordId + 'quantity------->' + quantity);
        
        Map<String, Object> quantityWrapper = (Map<String, Object>)JSON.deserializeUntyped(JSON.serialize(quantity));
               
        List<Map<String, Object>> quantityJSON = new List<Map<String, Object>>();
        
        for (Object instance : (List<Object>)quantityWrapper.get('quantityJSON'))
        quantityJSON.add((Map<String, Object>)instance);    
        
        system.debug('quantity:'+quantityJSON);
        
        
    }

JSON: Following are the draftValues from LWC Component.

[
  {
    "splitQuantityValue": "30",
    "Id": "row-0"
  },
  {
    "splitQuantityValue": "30",
    "Id": "row-1"
  },
  {
    "splitQuantityValue": "30",
    "Id": "row-2"
  }
]

Any kind of help is appreciated.

Answer 1

The error message you're getting provides a good hint here

System.TypeException: Invalid conversion from runtime type List to Map<String,ANY>`

In JSON, square braces [] indicate that you're working with an array, with a List. Curly braces {} indicate that you're working with an object, a Map<String, Object>.

Since the JSON you're working with starts with square braces, it's a List, and you need to deserialize it as a List, so:

• quantityWrapper needs to be declared as a List<Object>
• you need to cast the result of JSON.deserializeUntyped() as a List<Object>
• you don't need the loop at all (unless you're trying to gather or sum the individual quantities)