Checking for list of keys

[RedfoxSoftware]

I have a database query that is looking up the value for a set of IDs. I do not want to cache the entire list of IDs being looked up because that list passed in could change. However what would be useful is for each item passed in the list to be cached individually. I could then lookup each item and for those not cached, do a combined lookup from the database for all those values in one query. Finally the method should return the value, cached initially or not, for all the IDs passed in.

What is the best way to achieve this. Is it just to do something like:

 public async Task<List<T>> ProcessIds<T>(List<string> ids, string idType, Func<List<string>, Task<List<T>>> lookupFromDatabase)
    {
        var list1 = new List<T>();  // Items found in cache
        var list2 = new List<string>();  // Items not found in cache

        foreach (var id in ids)
        {
            var cacheKey = $"{idType}:{id}";
            if (_cache.TryGetValue(cacheKey, out T cachedItem))
            {
                list1.Add(cachedItem);
            }
            else
            {
                list2.Add(id);
            }
        }

        if (list2.Any())
        {
            // Perform database lookup for items not found in cache
            var itemsFromDatabase = await lookupFromDatabase(list2);

            // Set retrieved items in cache
            for (int i = 0; i < list2.Count; i++)
            {
                var cacheKey = $"{idType}:{list2[i]}";
                _cache.Set(cacheKey, itemsFromDatabase[i]);
                list1.Add(itemsFromDatabase[i]);
            }
        }

        // Retrieve all items from cache
        var finalResults = new List<T>();
        foreach (var id in ids)
        {
            var cacheKey = $"{idType}:{id}";
            if (_cache.TryGetValue(cacheKey, out T cachedItem))
            {
                finalResults.Add(cachedItem);
            }
        }

        return finalResults;
    }

[RedfoxSoftware]

The looks to be similar to #57 so you can ignore