C#快取初步學習

1. 快取是什么，各級快取

2. 本地快取原理和實作

3. 快取應用和快取更新

快取：為了快速獲取結果，在第一次獲取資料后存起來，下次直接使用

快取一般用在哪里？

1. 會重復的請求

2. 資料相對穩定

3. 耗時/耗資源

4. 體積不大

組態檔；選單-權限；省市區；類別資料；

熱搜；公告；技能/屬性；資料字典；

分頁(只要資料不是經常變)

如果一個資料快取一次，能夠被有效查詢4次，那這個快取就是值得的(大型系統的時候，為了性能，為了壓力，需要更多的快取)

快取本身是共享的，所以每個快取應該是唯一的

本地快取空間小，不能跨行程共享

小專案一般隨便快取

中大型專案不夠用的，一般就會使用分布式快取

如：

Memcached:記憶體管理

Redis: REmote DIctionary Server

下面附上我學習使用的自建簡單Cahce快取代碼：

/n        /// 執行緒安全的Dictionary集合/n        /// /n        public static Dictionary> CustomCacheDictionary;/n/n        /// 
/n        /// 快取需要自動清理:防止過多無用快取/n        /// 
/n        static CustomeCache()/n        {/n            CustomCacheDictionary = new Dictionary>();/n            Console.WriteLine($/"{DateTime.Now.ToString(/"MM-dd HH:mm:ss fff/")}初始化快取/");/n            Task.Run(() =>/n            {/n                while (true)/n                {/n                    LockAction(new Action(() => {/n                        List list = new List();/n                        foreach (var key in CustomCacheDictionary.Keys)/n                        {/n                            var valueTime = CustomCacheDictionary[key];/n                            if (valueTime.Value > DateTime.Now)/n                            {/n                                //沒有過期就不用管/n                            }/n                            else {/n                                //過期就統一將key放入list中/n                                list.Add(key);/n                            }/n                        }/n                        list.ForEach(key => CustomCacheDictionary.Remove(key));/n                    }));/n                    Thread.Sleep(1000 * 60 * 15);//每15分鐘清理一次/n                }/n            });/n        }/n/n        private static readonly object CustomCache_Lock = new object();/n        public static void LockAction(Action action)/n        {/n            lock (CustomCache_Lock)/n            {/n                action.Invoke();/n            }/n        }/n/n        /// 
/n        /// 添加快取資料/n        /// 
/n        /// /n        /// /n        /// /n        public static void Add(string key, object value, int second = 1800) {/n            LockAction(new Action(() =>/n            {/n                CustomCacheDictionary.Add(key, new KeyValuePair(value, DateTime.Now.AddSeconds(second)));/n            }));/n        }/n/n        /// 
/n        /// 保存資料  -存在則更新 不存在則新增/n        /// 
/n        /// /n        /// /n        /// /n        public static void SaveOrUpdate(string key, object value, int second = 1800) {/n            LockAction(new Action(() =>/n            {/n                CustomCacheDictionary[key] = new KeyValuePair(value, DateTime.Now.AddSeconds(second));/n            }));/n        }/n/n        public static T Find(string key, Func func, int second = 1800) {/n            T t = default(T);/n            if (!Exsit(key))/n            {/n                t = func.Invoke();/n                CustomeCache.Add(key, t, second);/n            }/n            else {/n                t = Get(key);/n            }/n            return t;/n        }/n/n        /// 
/n        /// 獲取資料 沒有則例外/n        /// 
/n        /// /n        /// /n        /// /n        public static T Get(string key) {/n            return (T)CustomCacheDictionary[key].Key;/n        }/n/n        /// 
/n        /// 檢查是否存在/n        /// 
/n        /// /n        /// /n        public static bool Exsit(string key)/n        {/n            if (CustomCacheDictionary.ContainsKey(key))/n            {/n                var valueTime = CustomCacheDictionary[key];/n                if (valueTime.Value > DateTime.Now)/n                {   //時候未到/n                    return true;/n                }/n                else {/n                    //時晨已到  上臺/n                    LockAction(new Action(() =>/n                    {/n                        CustomCacheDictionary.Remove(key);/n                    }));/n                    return false;/n                }/n            }/n            else {/n                return false;/n            }/n        }/n/n        public static void Remove(string key) {/n            LockAction(new Action(() =>/n            {/n                CustomCacheDictionary.Remove(key);/n            }));/n        }/n                /n        public static void RemoveAll() {/n            LockAction(new Action(() =>/n            {/n                CustomCacheDictionary.Clear();/n            }));/n        }/n/n        public static void RemoveCondition(Func func) {/n            LockAction(new Action(() =>/n            {/n                List list = new List();/n                foreach (var key in CustomCacheDictionary.Keys)/n                {/n                    if (func.Invoke(key))/n                    {/n                        list.Add(key);/n                    }/n                }/n                list.ForEach(key => CustomCacheDictionary.Remove(key));/n            }));/n        }/n/n    }","classes":[]}" data-cke-widget-upcasted="1" data-cke-widget-keep-attr="0" data-widget="codeSnippet">public class CustomeCache
    {
        /// <summary>
        /// 執行緒安全的Dictionary集合
        /// </summary>
        public static Dictionary<string, KeyValuePair<object, DateTime>> CustomCacheDictionary;

        /// <summary>
        /// 快取需要自動清理:防止過多無用快取
        /// </summary>
        static CustomeCache()
        {
            CustomCacheDictionary = new Dictionary<string, KeyValuePair<object, DateTime>>();
            Console.WriteLine($"{DateTime.Now.ToString("MM-dd HH:mm:ss fff")}初始化快取");
            Task.Run(() =>
            {
                while (true)
                {
                    LockAction(new Action(() => {
                        List<string> list = new List<string>();
                        foreach (var key in CustomCacheDictionary.Keys)
                        {
                            var valueTime = CustomCacheDictionary[key];
                            if (valueTime.Value > DateTime.Now)
                            {
                                //沒有過期就不用管
                            }
                            else {
                                //過期就統一將key放入list中
                                list.Add(key);
                            }
                        }
                        list.ForEach(key => CustomCacheDictionary.Remove(key));
                    }));
                    Thread.Sleep(1000 * 60 * 15);//每15分鐘清理一次
                }
            });
        }

        private static readonly object CustomCache_Lock = new object();
        public static void LockAction(Action action)
        {
            lock (CustomCache_Lock)
            {
                action.Invoke();
            }
        }

        /// <summary>
        /// 添加快取資料
        /// </summary>
        /// <param name="key"></param>
        /// <param name="value"></param>
        /// <param name="second"></param>
        public static void Add(string key, object value, int second = 1800) {
            LockAction(new Action(() =>
            {
                CustomCacheDictionary.Add(key, new KeyValuePair<object, DateTime>(value, DateTime.Now.AddSeconds(second)));
            }));
        }

        /// <summary>
        /// 保存資料  -存在則更新 不存在則新增
        /// </summary>
        /// <param name="key"></param>
        /// <param name="value"></param>
        /// <param name="second"></param>
        public static void SaveOrUpdate(string key, object value, int second = 1800) {
            LockAction(new Action(() =>
            {
                CustomCacheDictionary[key] = new KeyValuePair<object, DateTime>(value, DateTime.Now.AddSeconds(second));
            }));
        }

        public static T Find<T>(string key, Func<T> func, int second = 1800) {
            T t = default(T);
            if (!Exsit(key))
            {
                t = func.Invoke();
                CustomeCache.Add(key, t, second);
            }
            else {
                t = Get<T>(key);
            }
            return t;
        }

        /// <summary>
        /// 獲取資料 沒有則例外
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="key"></param>
        /// <returns></returns>
        public static T Get<T>(string key) {
            return (T)CustomCacheDictionary[key].Key;
        }

        /// <summary>
        /// 檢查是否存在
        /// </summary>
        /// <param name="key"></param>
        /// <returns></returns>
        public static bool Exsit(string key)
        {
            if (CustomCacheDictionary.ContainsKey(key))
            {
                var valueTime = CustomCacheDictionary[key];
                if (valueTime.Value > DateTime.Now)
                {   //時候未到
                    return true;
                }
                else {
                    //時晨已到  上臺
                    LockAction(new Action(() =>
                    {
                        CustomCacheDictionary.Remove(key);
                    }));
                    return false;
                }
            }
            else {
                return false;
            }
        }

        public static void Remove(string key) {
            LockAction(new Action(() =>
            {
                CustomCacheDictionary.Remove(key);
            }));
        }
                
        public static void RemoveAll() {
            LockAction(new Action(() =>
            {
                CustomCacheDictionary.Clear();
            }));
        }

        public static void RemoveCondition(Func<string, bool> func) {
            LockAction(new Action(() =>
            {
                List<string> list = new List<string>();
                foreach (var key in CustomCacheDictionary.Keys)
                {
                    if (func.Invoke(key))
                    {
                        list.Add(key);
                    }
                }
                list.ForEach(key => CustomCacheDictionary.Remove(key));
            }));
        }

    }

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