为什么要用？

有些时候经常会遇到重复提交的问题，为了避免这个问题，可以使用缓存锁的方式，主要是利用存取缓存比较快的原理。

当提交某个操作的时候，第一次提交会创建一个缓存，当有相同提交的时候，就可以判定为重复提交。当第一次提交完成或者抛错的时候，清除缓存。

使用什么方式？

使用AOP，也可以使用Filter，这里使用AOP：

public class CacheLockAttribute : BaseAOPAttribute
{
    readonly string _cacheKeyFormat;
    readonly string[] _keyDataFieldNames;
    readonly string _errorMessage;
    readonly int _objectIndex;
    readonly int _expiredMinutes;

    public CacheLockAttribute(string cacheKeyFormat, string[] keyDataFieldNames, string errorMessage,
        int objectIndex=0, int expiredMinutes=15)
    {
        _cacheKeyFormat = cacheKeyFormat;
        _keyDataFieldNames = keyDataFieldNames;
        _errorMessage = errorMessage;
        _objectIndex = objectIndex;
        _expiredMinutes = expiredMinutes;
    }

    string cacheKey = string.Empty;

    public override async Task Befor(IAOPContext context)
    {
        cacheKey = await CreateCacheKey(context);
        var cacheService = GetCacheService(context);
        if (await cacheService.HasCache(cacheKey))
        {
            throw new BusException(_errorMessage);
        }

        await cacheService.SetData(cacheKey, cacheKey, _expiredMinutes);
    }

    public override Task After(IAOPContext context) => ClearLockCache(context);

    public override Task HandlerException(IAOPContext context) => ClearLockCache(context);

    private async Task ClearLockCache(IAOPContext context)
    {
        if (cacheKey.IsNotNullOrEmpty())
        {
            var cacheService = GetCacheService(context);
            await cacheService.Remove(cacheKey);
        }
    }

    async Task<string> CreateCacheKey(IAOPContext context)
    {
        var obj = context.Arguments[_objectIndex];
        var cacheKeyDatas = _keyDataFieldNames.Select(s => obj.GetPropertyValue(s)).ToArray();
        return string.Format(_cacheKeyFormat, cacheKeyDatas);
    }

    ICacheService GetCacheService(IAOPContext context) => 
        context.ServiceProvider.GetService<ICacheService>();
}

单元测试：

public class CacheLockAopTests : BaseTests
{
    [Fact(DisplayName = "cache lock tests")]
    public async Task CacheLockTests()
    {
        var mockAop = new Mock<IAOPContext>();
        var mockCacheService = new Mock<ICacheService>();
        var cacheDict = new Dictionary<string, string>();
        var obj = new { Id = "123", Name = "james" };

        mockCacheService.Setup(m => m.HasCache(It.IsAny<string>()))
            .Returns((string s) => Task.FromResult(cacheDict.ContainsKey(s)));
        mockCacheService.Setup(m => m.SetData(It.IsAny<string>(), It.IsAny<string>(), It.IsAny<int>()))
            .Returns((string key, string value, int m) =>
            {
                cacheDict.Add(key, value);
                return Task.CompletedTask;
            });
        mockCacheService.Setup(m => m.Remove(It.IsAny<string>())).Returns((string key) =>
        {
            cacheDict.Remove(key);
            return Task.CompletedTask;
        });

        mockAop.Setup(a => a.ServiceProvider.GetService(typeof(ICacheService)))
            .Returns(() => mockCacheService.Object);

        mockAop.Setup(a => a.Arguments).Returns(() => new []{obj});
        CacheLockAttribute cacheLockAttribute_1 =
            new CacheLockAttribute("test_key_{0}_{1}", new[] { "Id", "Name" }, "test error");
        CacheLockAttribute cacheLockAttribute_2 =
            new CacheLockAttribute("test_key_{0}_{1}", new[] { "Id", "Name" }, "test error");
        await cacheLockAttribute_1.Befor(mockAop.Object);
        Assert.Single(cacheDict);
        await Assert.ThrowsAsync<BusException>(async () =>
        {
            await cacheLockAttribute_2.Befor(mockAop.Object);
        });
        Assert.Single(cacheDict);
        await cacheLockAttribute_1.After(mockAop.Object);
        Assert.Empty(cacheDict);
    }
    
}

如何使用？

在某个提交的方法上，加上[CacheLock(keyFormat, datafileds, errormessage, index, expiredMinutes]

• keyFormat：缓存键的Format
• datafileds：对象数据的字段名数组
• errormessage：抛错的错误信息
• index：参数中的第几个参数
• expiredMinutes：过期时间（分钟）默认15分钟

举例：

[CacheLock("payment_record_{0}", new []{"Id"}, "请不要重复提交")]
public async Task AddDataAsync(PaymentRecord data)
{
    await Task.Delay(5000);
}