完成7.5

第七章/内存缓存/Controllers/Test1Controller.cs

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+using Microsoft.AspNetCore.Mvc;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.Caching.Memory;
+
+[Route("[controller]/[action]")]
+[ApiController]
+public class Test1Controller : ControllerBase
+{
+    private readonly ILogger<Test1Controller> logger;
+    private readonly MyDbContext dbCtx;
+    private readonly IMemoryCache memCache;
+    public Test1Controller(MyDbContext dbCtx, IMemoryCache memCache, ILogger<Test1Controller> logger)
+    {
+        this.dbCtx = dbCtx;
+        this.memCache = memCache;
+        this.logger = logger;
+    }
+    [HttpGet]
+    public async Task<Book[]> GetBooks()
+    {
+        logger.LogInformation("开始执行GetBooks");
+        var items = await memCache.GetOrCreateAsync("AllBooks", async (e) =>
+        {
+            logger.LogInformation("从数据库中读取数据");
+            return await dbCtx.Books.ToArrayAsync();
+        });
+        logger.LogInformation("把数据返回给调用者");
+        return items;
+    }
+
+
+    [HttpGet]
+    public async Task<Book[]> Demo1()
+    {
+        //绝对过期时间
+        /*
+        logger.LogInformation("开始执行Demo1：" + DateTime.Now);
+        var items = await memCache.GetOrCreateAsync("AllBooks", async (e) => {
+            e.AbsoluteExpirationRelativeToNow = TimeSpan.FromSeconds(10);
+            logger.LogInformation("从数据库中读取数据");
+            return await dbCtx.Books.ToArrayAsync();
+        });
+        logger.LogInformation("Demo1执行结束");*/
+        //滑动过期时间
+        /*
+        logger.LogInformation("开始执行Demo2：" + DateTime.Now);
+        var items = await memCache.GetOrCreateAsync("AllBooks2", async (e) => {
+            e.SlidingExpiration = TimeSpan.FromSeconds(10);
+            logger.LogInformation("Demo2从数据库中读取数据");
+            return await dbCtx.Books.ToArrayAsync();
+        });
+        logger.LogInformation("Demo2执行结束");
+        */
+        //混合使用过期时间策略
+        logger.LogInformation("开始执行Demo3：" + DateTime.Now);
+        var items = await memCache.GetOrCreateAsync("AllBooks3", async (e) => {
+            e.SlidingExpiration = TimeSpan.FromSeconds(10);
+            e.AbsoluteExpirationRelativeToNow = TimeSpan.FromSeconds(30);
+            logger.LogInformation("Demo3从数据库中读取数据");
+            return await dbCtx.Books.ToArrayAsync();
+        });
+        logger.LogInformation("Demo3执行结束");
+
+        return items;
+    }
+
+}

第七章/内存缓存/IMemoryCacheHelper.cs

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+using Microsoft.Extensions.Caching.Memory;
+
+namespace Zack.ASPNETCore
+{
+    public interface IMemoryCacheHelper
+    {
+        /// <summary>
+        /// 从缓存中获取数据，如果缓存中没有数据，则调用valueFactory获取数据。
+        /// 可以用AOP+Attribute的方式来修饰到Service接口中实现缓存，更加优美，但是没有这种方式更灵活。
+        /// 默认最长的缓存过期时间是expireSeconds秒，当然也可以在领域事件的Handler中调用Update更新缓存，或者调用Remove删除缓存。
+        /// 因为IMemoryCache会把null当成合法的值，因此不会有缓存穿透的问题，但是还是建议用我这里封装的ICacheHelper，原因如下：
+        /// 1）可以切换别的实现类，比如可以保存到MemCached、Redis等地方。这样可以隔离变化。
+        /// 2）IMemoryCache的valueFactory用起来麻烦，还要单独声明一个ICacheEntry参数，大部分时间用不到这个参数。
+        /// 3）这里把expireSeconds加上了一个随机偏差，这样可以避免短时间内同样的请求集中过期导致“缓存雪崩”的问题
+        /// 4）这里加入了缓存数据的类型不能是IEnumerable、IQueryable等类型的限制
+        /// </summary>
+        /// <typeparam name="TResult">缓存的值的类型</typeparam>
+        /// <param name="cacheKey">缓存的key</param>
+        /// <param name="valueFactory">提供数据的委托</param>
+        /// <param name="expireSeconds">缓存过期秒数的最大值，实际缓存时间是在[expireSeconds,expireSeconds*2)之间，这样可以一定程度上避免大批key集中过期导致的“缓存雪崩”的问题</param>
+        /// <returns></returns>
+        TResult? GetOrCreate<TResult>(string cacheKey, Func<ICacheEntry, TResult?> valueFactory, int expireSeconds = 60);
+
+        Task<TResult?> GetOrCreateAsync<TResult>(string cacheKey, Func<ICacheEntry, Task<TResult?>> valueFactory, int expireSeconds = 60);
+
+        /// <summary>
+        /// 删除缓存的值
+        /// </summary>
+        /// <param name="cacheKey"></param>
+        void Remove(string cacheKey);
+    }
+}

第七章/内存缓存/MemoryCacheHelper.cs

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+using Microsoft.Extensions.Caching.Memory;
+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+
+namespace Zack.ASPNETCore
+{
+    /// <summary>
+    /// 用ASP.NET的IMemoryCache实现的内存缓存
+    /// </summary>
+    public class MemoryCacheHelper : IMemoryCacheHelper
+    {
+        private readonly IMemoryCache memoryCache;
+        public MemoryCacheHelper(IMemoryCache memoryCache)
+        {
+            this.memoryCache = memoryCache;
+        }
+
+        private static void ValidateValueType<TResult>()
+        {
+            //因为IEnumerable、IQueryable等有延迟执行的问题，造成麻烦，因此禁止用这些类型
+            Type typeResult = typeof(TResult);
+            if (typeResult.IsGenericType)//如果是IEnumerable<String>这样的泛型类型，则把String这样的具体类型信息去掉，再比较
+            {
+                typeResult = typeResult.GetGenericTypeDefinition();
+            }
+            //注意用相等比较，不要用IsAssignableTo
+            if (typeResult == typeof(IEnumerable<>) || typeResult == typeof(IEnumerable)
+                || typeResult == typeof(IAsyncEnumerable<TResult>)
+                || typeResult == typeof(IQueryable<TResult>) || typeResult == typeof(IQueryable))
+            {
+                throw new InvalidOperationException($"TResult of {typeResult} is not allowed, please use List<T> or T[] instead.");
+            }
+        }
+
+        private static void InitCacheEntry(ICacheEntry entry, int baseExpireSeconds)
+        {
+            //过期时间.Random.Shared 是.NET6新增的
+            double sec = Random.Shared.Next(baseExpireSeconds, baseExpireSeconds * 2);
+            TimeSpan expiration = TimeSpan.FromSeconds(sec);
+            entry.AbsoluteExpirationRelativeToNow = expiration;
+        }
+
+        public TResult? GetOrCreate<TResult>(string cacheKey, Func<ICacheEntry, TResult?> valueFactory, int baseExpireSeconds = 60)
+        {
+            ValidateValueType<TResult>();
+            //因为IMemoryCache保存的是一个CacheEntry，所以null值也认为是合法的，因此返回null不会有“缓存穿透”的问题
+            //不调用系统内置的CacheExtensions.GetOrCreate，而是直接用GetOrCreate的代码，这样免得包装一次委托
+            if (!memoryCache.TryGetValue(cacheKey, out TResult result))
+            {
+                using ICacheEntry entry = memoryCache.CreateEntry(cacheKey);
+                InitCacheEntry(entry, baseExpireSeconds);
+                result = valueFactory(entry)!;
+                entry.Value = result;
+            }
+            return result;
+        }
+
+        public async Task<TResult?> GetOrCreateAsync<TResult>(string cacheKey, Func<ICacheEntry, Task<TResult?>> valueFactory, int baseExpireSeconds = 60)
+        {
+            ValidateValueType<TResult>();
+            if (!memoryCache.TryGetValue(cacheKey, out TResult result))
+            {
+                using ICacheEntry entry = memoryCache.CreateEntry(cacheKey);
+                InitCacheEntry(entry, baseExpireSeconds);
+                result = (await valueFactory(entry))!;
+                entry.Value = result;
+            }
+            return result;
+        }
+
+        public void Remove(string cacheKey)
+        {
+            memoryCache.Remove(cacheKey);
+        }
+    }
+}

第七章/内存缓存/Program.cs

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+using Microsoft.EntityFrameworkCore;
+using Zack.ASPNETCore;
+
+var builder = WebApplication.CreateBuilder(args);
+
+// Add services to the container.
+
+builder.Services.AddControllers();
+// Learn more about configuring Swagger/OpenAPI at https://aka.ms/aspnetcore/swashbuckle
+builder.Services.AddEndpointsApiExplorer();
+builder.Services.AddSwaggerGen();
+builder.Services.AddMemoryCache();
+builder.Services.AddDbContext<MyDbContext>(opt => {
+    string connStr = builder.Configuration.GetConnectionString("Default");
+    opt.UseSqlServer(connStr);
+});
+builder.Services.AddScoped<IMemoryCacheHelper, MemoryCacheHelper>();
+var app = builder.Build();
+
+// Configure the HTTP request pipeline.
+if (app.Environment.IsDevelopment())
+{
+    app.UseSwagger();
+    app.UseSwaggerUI();
+}
+
+app.UseHttpsRedirection();
+
+app.UseAuthorization();
+
+app.MapControllers();
+
+app.Run();

第七章/内存缓存/Properties/launchSettings.json

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+{
+  "$schema": "https://json.schemastore.org/launchsettings.json",
+  "iisSettings": {
+    "windowsAuthentication": false,
+    "anonymousAuthentication": true,
+    "iisExpress": {
+      "applicationUrl": "http://localhost:30021",
+      "sslPort": 44344
+    }
+  },
+  "profiles": {
+    "内存缓存": {
+      "commandName": "Project",
+      "dotnetRunMessages": true,
+      "launchBrowser": true,
+      "launchUrl": "swagger",
+      "applicationUrl": "https://localhost:7134;http://localhost:5134",
+      "environmentVariables": {
+        "ASPNETCORE_ENVIRONMENT": "Development"
+      }
+    },
+    "IIS Express": {
+      "commandName": "IISExpress",
+      "launchBrowser": true,
+      "launchUrl": "swagger",
+      "environmentVariables": {
+        "ASPNETCORE_ENVIRONMENT": "Development"
+      }
+    }
+  }
+}

第七章/内存缓存/appsettings.Development.json

@@ -0,0 +1,8 @@
+{
+  "Logging": {
+    "LogLevel": {
+      "Default": "Information",
+      "Microsoft.AspNetCore": "Warning"
+    }
+  }
+}

第七章/内存缓存/appsettings.json

@@ -0,0 +1,5 @@
+{
+	"ConnectionStrings": {
+		"Default": "Server=.;Database=demo8;Trusted_Connection=True;"
+	}
+}

第七章/内存缓存/内存缓存.csproj

@@ -0,0 +1,30 @@
+<Project Sdk="Microsoft.NET.Sdk.Web">
+
+  <PropertyGroup>
+    <TargetFramework>net6.0</TargetFramework>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Swashbuckle.AspNetCore" Version="6.2.3" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\BooksEFCore\BooksEFCore.csproj" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <Content Update="appsettings.Development.json">
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+      <ExcludeFromSingleFile>true</ExcludeFromSingleFile>
+      <CopyToPublishDirectory>PreserveNewest</CopyToPublishDirectory>
+    </Content>
+    <Content Update="appsettings.json">
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+      <ExcludeFromSingleFile>true</ExcludeFromSingleFile>
+      <CopyToPublishDirectory>PreserveNewest</CopyToPublishDirectory>
+    </Content>
+  </ItemGroup>
+
+</Project>

第七章/分布式缓存/Controllers/Test1Controller.cs

@@ -0,0 +1,39 @@
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.Extensions.Caching.Distributed;
+using Zack.ASPNETCore;
+
+namespace 分布式缓存.Controllers
+{
+    [ApiController]
+    [Route("[controller]/[action]")]
+    public class Test1Controller : ControllerBase
+    {
+		private readonly IDistributedCache distCache;
+		private readonly IDistributedCacheHelper helper;
+        public Test1Controller(IDistributedCache distCache, IDistributedCacheHelper helper)
+        {
+            this.distCache = distCache;
+            this.helper = helper;
+        }
+        [HttpGet]
+		public string Now()
+		{
+			string s = distCache.GetString("Now");
+			if (s == null)
+			{
+				s = DateTime.Now.ToString();
+				var opt = new DistributedCacheEntryOptions();
+				opt.AbsoluteExpirationRelativeToNow = TimeSpan.FromSeconds(30);
+				distCache.SetString("Now", s, opt);
+			}
+			return s;
+		}
+
+		[HttpGet]
+		public Task<string?> Now2()
+        {
+			return helper.GetOrCreateAsync<string>("Now2", async e => DateTime.Now.ToString());
+        }
+
+	}
+}