.Net Core 缓存方式（二）自定义分布式缓存的扩展方法（5）

IDistributedCache 的扩展方法

IDistributedCache 的扩展方法实现了类似于 cache.GetString(key); 这种写法，但是实际使用起来还需要写多行 类转字符串的代码，这时候就可以自己自定义 IDistributedCache 的扩展方法。

实现类似 MemoryCache的GetOrCreate方法

_cache.GetOrCreate

    var cacheEntry = _cache.GetOrCreate(CacheKeys.Entry, entry =>    {        entry.SlidingExpiration = TimeSpan.FromSeconds(3);        return DateTime.Now;    });

MemoryCache的GetOrCreate好用，看下实现方法：

        public static TItem GetOrCreate<TItem>(this IMemoryCache cache, object key, Func<ICacheEntry, TItem> factory)        {            if (!cache.TryGetValue(key, out object result))            {                ICacheEntry entry = cache.CreateEntry(key);                result = factory(entry);                entry.SetValue(result);                // need to manually call dispose instead of having a using                // in case the factory passed in throws, in which case we                // do not want to add the entry to the cache                entry.Dispose();            }            return (TItem)result;        }

我们可以写个类似 GetOrCreate 的扩展方法

        public static TItem GetOrCreate<TItem>(this IDistributedCache cache, string key, Func<TItem> factory, DistributedCacheEntryOptions options)        {            if (!cache.TryGetValue(key, out TItem obj))            {                obj = factory();                cache.Set(key, obj, options);            }            return (TItem)obj;        }

自定义分布式缓存的扩展方法

我这里设置默认 半小时过期

    public static class DistributedCacheExtensions    {        private static readonly DistributedCacheEntryOptions DefaultOptions = new DistributedCacheEntryOptions().SetAbsoluteExpiration(TimeSpan.FromMinutes(30));        public static TItem Get<TItem>(this IDistributedCache cache, string key)        {            try            {                var valueString = cache.GetString(key);                if (string.IsNullOrEmpty(valueString))                {                    return default(TItem);                }                return JsonSerializer.Deserialize<TItem>(valueString);            }            catch (Exception e)            {                return default(TItem);            }        }        public static async Task<TItem> GetAsync<TItem>(this IDistributedCache cache, string key, CancellationToken token = default(CancellationToken))        {            try            {                var valueString = await cache.GetStringAsync(key, token);                if (string.IsNullOrEmpty(valueString))                {                    return default(TItem);                }                return JsonSerializer.Deserialize<TItem>(valueString);            }            catch (Exception e)            {                return default(TItem);            }        }        public static bool TryGetValue<TItem>(this IDistributedCache cache, string key, out TItem value)        {            var valueString = cache.GetString(key);            if (!string.IsNullOrEmpty(valueString))            {                value = JsonSerializer.Deserialize<TItem>(valueString);                return true;            }            value = default(TItem);            return false;        }        public static void Set<TItem>(this IDistributedCache cache, string key, TItem value)        {            cache.SetString(key, JsonSerializer.Serialize(value), DefaultOptions);        }        public static void Set<TItem>(this IDistributedCache cache, string key, TItem value, DistributedCacheEntryOptions options)        {            cache.SetString(key, JsonSerializer.Serialize(value), options);        }        public static async Task SetAsync<TItem>(this IDistributedCache cache, string key, TItem value, CancellationToken token = default(CancellationToken))        {            await cache.SetStringAsync(key, JsonSerializer.Serialize(value), DefaultOptions, token);        }        public static async Task SetAsync<TItem>(this IDistributedCache cache, string key, TItem value, DistributedCacheEntryOptions options, CancellationToken token = default(CancellationToken))        {            await cache.SetStringAsync(key, JsonSerializer.Serialize(value), options, token);        }        public static TItem GetOrCreate<TItem>(this IDistributedCache cache, string key, Func<TItem> factory)        {            if (!cache.TryGetValue(key, out TItem obj))            {                obj = factory();                cache.Set(key, obj);            }            return (TItem)obj;        }        public static TItem GetOrCreate<TItem>(this IDistributedCache cache, string key, Func<TItem> factory, DistributedCacheEntryOptions options)        {            if (!cache.TryGetValue(key, out TItem obj))            {                obj = factory();                cache.Set(key, obj, options);            }            return (TItem)obj;        }        public static async Task<TItem> GetOrCreateAsync<TItem>(this IDistributedCache cache, string key, Func<Task<TItem>> factory)        {            if (!cache.TryGetValue(key, out TItem obj))            {                obj = await factory();                await cache.SetAsync(key, obj);            }            return (TItem)obj;        }        public static async Task<TItem> GetOrCreateAsync<TItem>(this IDistributedCache cache, string key, Func<Task<TItem>> factory, DistributedCacheEntryOptions options)        {            if (!cache.TryGetValue(key, out TItem obj))            {                obj = await factory();                await cache.SetAsync(key, obj, options);            }            return (TItem)obj;        }    }

用法 example：

        private readonly IDistributedCache _distributedCache;        public CategoryService(            IDistributedCache distributedCache)        {            _distributedCache = distributedCache;        }        public async Task<List<CategoryList>> GetCategoryList()        {            return await _distributedCache.GetOrCreateAsync(ProductCaching.GetCategoryList,                 async () => await GetFormHybris());        }            var saveCode = _distributedCache.Get<string>(cacheKey);            var order= _distributedCache.Get<Order>(cacheKey);