How to merge existing and incoming data

Help
1

Is there a way on how we can be able to merge the existing and incoming data? I am using cache for the data, however, even if the data has been updated, I can still get the previous value (existing) and I am not sure how to display the incoming data. Here is my code:

Query: {
    fields: {
      category: {
        keyArgs: ['categoryid'],
        read (data: any) {
          return data;
        },
        merge (existing: any, incoming: any) {
          if (!existing) return incoming;
          return {
            ...incoming,
            data: {
              ...existing.data,
              items: [...existing.data.items, incoming.data.items]
              pagination: incoming.data.pagination
            }
          };
        }
      },
    }
  },

And here is my data:

existing = {
categoryid: 10,
 items: [
{
        "productid": "123",
        "isnew": true
    },
    {
        "productid": "456",
        "isnew": true,
    }
]
}

incoming = {
categoryid: 10,
 items: [
{
        "productid": "123",
        "isnew": false
    },
    {
        "productid": "456",
        "isnew": false,
    }
]
}

Really appreciate it if someone can help me. Thanks