分布式缓存是由多个应用服务器共享的缓存，通常作为外部服务存储在单个应用服务器上，常用的有SqlServer，Redis，NCache。
分布式缓存可以提高ASP.NET Core应用程序的性能和可伸缩性，尤其是应用程序由云服务或服务器场托管时。
分布式缓存的特点：
- 跨多个服务器请求，保证一致性。
- 应用程序的服务器重启或部署时，缓存数据不丢失。
- 不使用本地缓存（如果是多个应用服务器会出现不一致及数据丢失的风险）
Sql Server Distrubuted Cahce configure and application
1、Nuget下载安装包
2、使用sql-cache 工具创建缓存列表
Win+r 打开cmd命令，输入如下指令，创建缓存表，
dotnet sql-cache create "Data Source=(localdb)\MSSQLLocalDB;Initial Catalog=DistCache;Integrated Security=True;" dbo TestCache
如遇到以下error，需要安装dotnet-sql-cache，命令如下。（Note: NetCore 3.1 对应的dotnet-sql-chche version 3.1.13）
dotnet tool install --global dotnet-sql-cache
如果看到如下提示，证明缓存表创建成功：
缓存表结构：
3、在请求管道中添加DistributedCache（Note：这里建议ConnectionString，SchemaName，TableName最好写在配置文件里，在本章最后简单介绍下如果在NetCore console 里配置使用appsettings.json）
public static IServiceCollection ConfigureServices(this IServiceCollection services)
{
var configuration = BuildConfiguration();
services.AddSingleton<IConfiguration>(configuration);
services.AddDistributedSqlServerCache(options=>
{
options.ConnectionString = configuration["SqlServerDistributedCache:ConnectionString"];
options.SchemaName =configuration["SqlServerDistributedCache:SchemaName"];
options.TableName = configuration["SqlServerDistributedCache:TableName"];
});
services.AddTransient<ISqlServerService, SqlServerService>();
return services;
}
4、通过构造函数依赖注入IDistributedCache
private readonly IDistributedCache _cacheService; public SqlServerService(IDistributedCache cacheService)
{
this._cacheService = cacheService;
}
最简单的方式是直接使用IDistributedCache Extension方法，提供了String类型的cache value还是比较常用的。
以下是简单封装实现，根据需求更改即可。
public class SqlServerService: ISqlServerService
{
private readonly IDistributedCache _cacheService; public SqlServerService(IDistributedCache cacheService)
{
this._cacheService = cacheService;
} public async Task SetAsync(string key, byte[] value, object expiration = null, bool isAbsoluteExpiration = false)
{
var options = this.BuildDistributedCacheEntryOptions(expiration, isAbsoluteExpiration);
await _cacheService.SetAsync(key, value, options);
} public async Task SetAsync(string key, string value, object expiration = null, bool isAbsoluteExpiration = false)
{
var options = this.BuildDistributedCacheEntryOptions(expiration, isAbsoluteExpiration);
await _cacheService.SetStringAsync(key, value, options);
} public async Task<byte[]> GetAsync(string key)
{
return await _cacheService.GetAsync(key);
} public async Task<string> GetStringAsync(string key)
{
return await _cacheService.GetStringAsync(key);
} public async Task RemoveAsync(string key)
{
await _cacheService.RemoveAsync(key);
} public async Task RefreshAsync(string key)
{
await _cacheService.RefreshAsync(key);
} private DistributedCacheEntryOptions BuildDistributedCacheEntryOptions(object expiration = null, bool isAbsoluteExpiration = false)
{
var options = new DistributedCacheEntryOptions();
if (expiration != null)
{
if (expiration is TimeSpan)
{
if (isAbsoluteExpiration)
options.SetAbsoluteExpiration((TimeSpan)expiration);
else
options.SetSlidingExpiration((TimeSpan)expiration);
}
else if (expiration is DateTimeOffset)
{
options.SetAbsoluteExpiration((DateTimeOffset)expiration);
}
else
{
throw new NotSupportedException("Not support current expiration object settings.");
}
}
return options;
}
}
这里主要说下DistributedCacheEntryOptions这个类，作用是设置缓存项的过期时间
public class DistributedCacheEntryOptions
{
public DistributedCacheEntryOptions()
public DateTimeOffset? AbsoluteExpiration { get; set; }//绝对过期时间
public TimeSpan? AbsoluteExpirationRelativeToNow { get; set; }//绝对过期时间
public TimeSpan? SlidingExpiration { get; set; } //滑动过期时间（如果在滑动过期时间内刷新，将重新设置滑动过去时间，对应IDistributedCache中的Refresh方法）
}
OK，Sql Server IDistributeCache 就介绍到这里。
附加：NetCore Console 中使用appsettings.json文件
1、Nuget下载安装packages
2、添加appsettings.json文件，修改property->copy always
"SqlServerDistributedCache": {
"ConnectionString": "",
"SchemaName": "",
"TableName": ""
}
3、构建Configuration对象并添加到请求管道
public static IServiceCollection ConfigureServices(this IServiceCollection services)
{
var configuration = BuildConfiguration();
services.AddSingleton<IConfiguration>(configuration);
services.AddDistributedSqlServerCache(options=>
{
options.ConnectionString = configuration["SqlServerDistributedCache:ConnectionString"];
options.SchemaName = configuration["SqlServerDistributedCache:SchemaName"];
options.TableName = configuration["SqlServerDistributedCache:TableName"];
});
services.AddTransient<ISqlServerService, SqlServerService>();
return services;
} private static IConfigurationRoot BuildConfiguration()
{
var env = Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT"); var builder = new ConfigurationBuilder()
.SetBasePath(Directory.GetCurrentDirectory())
.AddJsonFile($"appsettings.json", true, true)
.AddJsonFile($"appsettings.{env}.json", true, true)
.AddEnvironmentVariables();
return builder.Build();
}
这里是根据环境变量“ASPNETCORE_ENVIRONMENT”读取不同的appsettings文件，比如Development，Staging，Product
4、通过构造函数注入使用IConfiguration对象即可。
完整代码地址： Github。