refactor(LookupService): add cache logic for LookupService sample

src/BootstrapBlazor.Server/Services/DemoLookupService.cs

@@ -3,26 +3,55 @@
 // See the LICENSE file in the project root for more information.
 // Maintainer: Argo Zhang([email protected]) Website: https://www.blazor.zone
 
+using System.Collections.Concurrent;
+
 namespace Microsoft.Extensions.DependencyInjection;
 
 /// <summary>
 /// 演示网站示例数据注入服务实现类
 /// </summary>
 internal class DemoLookupService(IServiceProvider provider) : LookupServiceBase
 {
-    private IServiceProvider Provider { get; } = provider;
+    /// <summary>
+    /// <inheritdoc/>
+    /// </summary>
+    /// <param name="key"></param>
+    /// <param name="data"></param>
+    /// <returns></returns>
+    public override IEnumerable<SelectedItem>? GetItemsByKey(string? key, object? data) => null;
+
+    private static readonly ConcurrentDictionary<string, List<SelectedItem>> _cache = [];
 
-    public override IEnumerable<SelectedItem>? GetItemsByKey(string? key, object? data)
+    /// <summary>
+    /// <inheritdoc/>
+    /// </summary>
+    /// <param name="key"></param>
+    /// <param name="data"></param>
+    /// <returns></returns>
+    public override async Task<IEnumerable<SelectedItem>?> GetItemsByKeyAsync(string? key, object? data)
     {
         IEnumerable<SelectedItem>? items = null;
         if (key == "Foo.Complete")
         {
-            var localizer = Provider.GetRequiredService<IStringLocalizer<Foo>>();
-            items = new List<SelectedItem>()
+            // 使用缓存技术防止多次调用提高应用性能
+            if (_cache.TryGetValue(key, out var value))
             {
-                new() { Value = "True", Text = localizer["True"].Value },
-                new() { Value = "False", Text = localizer["False"].Value }
-            };
+                items = value;
+            }
+            else
+            {
+                // 模拟异步延时实战中大概率从数据库中获得数据
+                await Task.Delay(1);
+
+                var localizer = provider.GetRequiredService<IStringLocalizer<Foo>>();
+                var v = new List<SelectedItem>()
+                {
+                    new() { Value = "True", Text = localizer["True"].Value },
+                    new() { Value = "False", Text = localizer["False"].Value }
+                };
+                _cache.TryAdd(key, v);
+                items = v;
+            }
         }
         return items;
     }