Question

我正在尝试创建IMemoryCache.TryGetValue方法的模拟，但是当它命中cache.Get(cacheKey)时会返回以下错误：

无法转换类型为'System.Collections.Generic.List 1[ConnectionsModel]' to type 'System.Threading.Tasks.Task 1 [System.Collections.Generic.List`1 [ConnectionsModel]
的对象

这里是模拟：

 private static Mock<IMemoryCache> ConfigureMockCacheWithDataInCache(List<ConnectionsModel> auth0ConnectionsResponse)
 {
        object value = auth0ConnectionsResponse;
        var mockCache = new Mock<IMemoryCache>();
        mockCache
            .Setup(x => x.TryGetValue(
                It.IsAny<object>(), out value
            ))
            .Returns(true);
        return mockCache;
    }

这是测试方法：

var connectionList = new List<ConnectionsModel>();
var connectionsModel= new ConnectionsModel()
{
     id = "1",
    name = "abc",
    enabled_cons = new List<string>() { "test" }
};
connectionList.Add(connectionsModel);
var mockObject = ConfigureMockCacheWithDataInCache(connectionList);
var sut = new MyService(mockCache.Object);
// Act
var result = await sut.GetConnection(_clientId);

这是它命中的服务：

public async Task<ConnectionsModel> GetConnection(string clientId)
{
    var connections = await _cacheService.GetOrSet("cacheKey", ()=> CallBack());
    var connection = connections.FirstOrDefault();
    return connection;
}
private async Task<List<ConnectionsModel>> CallBack()
{
    string url = url;
    _httpClient.BaseAddress = new Uri(BaseUrl);
    var response = await _httpClient.GetAsync(url);
    response.EnsureSuccessStatusCode();
    return await response.Content.ReadAsAsync<List<ConnectionsModel>>();
}

和缓存扩展方法：

   public static T GetOrSet<T>(this IMemoryCache cache, string cacheKey, Func<T> getItemCallback, double cacheTimeout = 86000) where T : class
    {
        T item = cache.Get<T>(cacheKey);
        if (item == null)
        {
            item = getItemCallback();
            cache.Set(cacheKey, item, DateTime.Now.AddSeconds(cacheTimeout));
        }
        return item;
    }

此行T item = cache.Get<T>(cacheKey);之后，我得到了上述异常。我该如何解决？

Answer 1

考虑为扩展创建额外的重载，以允许使用异步API

public static async Task<T> GetOrSet<T>(this IMemoryCache cache, string cacheKey, Func<Task<T>> getItemCallback, double cacheTimeout = 86000) where T : class
{
    T item = cache.Get<T>(cacheKey);
    if (item == null)
    {
        item = await getItemCallback();
        cache.Set(cacheKey, item, DateTime.Now.AddSeconds(cacheTimeout));
    }
    return item;
}

Answer 2

在扩展方法中，您正在呼叫getItemCallback()而不等待它。该lambda会在您的服务中调用您的Callback方法，这是异步的，因此也是异步的。结果，您将item设置为Task<List<ConnectionsModel>>并尝试将其返回为List<ConnectionsModel>。

item = await getItemCallback();

将Generic.List转换为System.Threading.Task.Generic.List时遇到问题

2 个答案: