如何在执行 Polly 策略时包含 return 语句？

问题描述

以下是我在 C# Windows 应用程序中的代码，其中处理了与 Oracle、FTP 和空引用异常的连接：

{'__header__': b'MATLAB 5.0 MAT-file,Platform: PCWIN64,Created on: qua jul 21 08:43:40 2021','__version__': '1.0','__globals__': [],'u_x': array([[ 0.00000000e+00,1.39250848e-07,8.35505086e-07,...,2.99900000e+01,2.99968199e+01,3.00000000e+01],[ 0.00000000e+00,-5.48522290e-11,-1.97447920e-09,5.29180779e+00,5.22323380e+00,5.20265331e+00]])}

使用这段代码，我不能在函数中间使用 <script src="/v2/resources.js" defer=""></script> 关键字，因为 Polly 框架不允许这样做。

您能否建议在函数中间处理 public Result Execute() { Result result = null; string errorMessage = string.Empty; var retryTimes = 1000; var retryableErrorCodes = new[] { "ORA-03113","ORA-03114","ORA-12543","ORA-12170","ORA-12154","ORA-12541","ORA-12560","ORA-03135","Connection request timed out" }; var retryExceptionError = new[] { "Object reference not set to an instance of an object" }; RetryPolicy retryPolicyFTP = Policy .Handle<Xceed.Ftp.FtpInvalidStateException>().Or<Xceed.Ftp.FtpIOException>() .WaitAndRetry(retryTimes,_ => TimeSpan.FromSeconds(1)); RetryPolicy retryPolicyOracle = Policy .Handle<OracleException>(ex => retryableErrorCodes.Any(errorCode => ex.Message.ToString().Contains(errorCode))) .WaitAndRetry(retryTimes,_ => TimeSpan.FromSeconds(1)); RetryPolicy retryException = Policy .Handle<Exception>(ex => retryExceptionError.Any(errorCode => ex.Message.ToString().Contains(errorCode))) .WaitAndRetry(retryTimes,_ => TimeSpan.FromSeconds(1)); Policy.Wrap(retryPolicyFTP,retryPolicyOracle,retryException).Execute(() => { //few lines of C# Code like fetching details from Database if(some condition) { //Some Operations return new Result(ResultType.Failure,"This function has Failed"); } if(some other condition) { //Some Operations return new Result(ResultType.Success,"This function is Successful"); } //Some more lines of C# Code }); return Result.Successful; } 关键字的更好方法是什么？

解决方法

在 Polly 中，您可以为方法和函数定义装饰器。

如果是方法，重试策略应该这样定义：

RetryPolicy retryPolicyFTP = Policy
    .Handle<Xceed.Ftp.FtpInvalidStateException>().Or<Xceed.Ftp.FtpIOException>()
    .WaitAndRetry(retryTimes,_ => TimeSpan.FromSeconds(1));

如果是函数，重试策略应该这样定义：

RetryPolicy<Result> retryPolicyFTP = Policy<Result>
    .Handle<Xceed.Ftp.FtpInvalidStateException>().Or<Xceed.Ftp.FtpIOException>()
    .WaitAndRetry(retryTimes,_ => TimeSpan.FromSeconds(1));

您也应该在这里找到 lhs 和 rhs 上的 <Result> 部分。

---

有了这些知识，您的方法可以像这样重写：

public Result Execute()
{
    Result result = null;
    string errorMessage = string.Empty;

    var retryTimes = 1000;
    var retryableErrorCodes = new[] { "ORA-03113","ORA-03114","ORA-12543","ORA-12170","ORA-12154","ORA-12541","ORA-12560","ORA-03135","Connection request timed out" };
    var retryExceptionError = new[] { "Object reference not set to an instance of an object" };

    RetryPolicy<Result> retryPolicyFTP = Policy<Result>
        .Handle<Xceed.Ftp.FtpInvalidStateException>().Or<Xceed.Ftp.FtpIOException>()
        .WaitAndRetry(retryTimes,_ => TimeSpan.FromSeconds(1));

    RetryPolicy<Result> retryPolicyOracle = Policy<Result>
        .Handle<OracleException>(ex => retryableErrorCodes.Any(errorCode => ex.Message.ToString().Contains(errorCode)))
        .WaitAndRetry(retryTimes,_ => TimeSpan.FromSeconds(1));

    RetryPolicy<Result> retryException = Policy<Result>
        .Handle<Exception>(ex => retryExceptionError.Any(errorCode => ex.Message.ToString().Contains(errorCode)))
        .WaitAndRetry(retryTimes,_ => TimeSpan.FromSeconds(1));

    Result res = Policy.Wrap(retryPolicyFTP,retryPolicyOracle,retryException).Execute(() =>
    {
        if (some condition)
        {
            return new Result(ResultType.Failure,"This function has Failed");
        }
        if (some other condition)
        {
            return new Result(ResultType.Success,"This function is Successful");
        }
        return Result.Successful;
    });
    return res;
}

因为您的 Execute 必须返回 Result，这就是 Result.Successful 可以移动到 Execute 块内的原因。

---

我还建议像这样将策略声明和执行分开：

public Result Execute()
{
    ...

    var strategy = Policy.Wrap(retryPolicyFTP,retryException)
    return strategy.Execute(() =>
    {
        if (some condition)
        {
            return new Result(ResultType.Failure,"This function is Successful");
        }
        return Result.Successful;
    });
}