仅当 Option 为 Some 值而非 None 时才调用 Langext MapAsync

发布于 2025-01-14 08:19:55 字数 651 浏览 2 评论 0原文

我使用 LangExt 库，并且存在 UserId 1 不存在用户的情况。

public async Task<Option<UserViewModel> GetUser()
=> await GetUser(1)
          .MapAsync(this.alterName)
          .MapAsync(this.alterCountry)
          .MapAsync(this.applyMoreChange)
          .Map(this.mapper.map<ViewModel>);

由于 userId 1 不存在用户，因此 GetUser(1) 返回 Option 并且其余代码失败并出现异常

LangExt.ValueIsNoneException : Value is None.
at languageExt.OptionAsyncAwaiter`1.GetResult()

How to handle this case.?并确保仅当选项是某个用户而不是无用户时才执行 mapAsync 和 map 链接。

原文

I use LangExt library and i have the case of no user exists with UserId 1.

public async Task<Option<UserViewModel> GetUser()
=> await GetUser(1)
          .MapAsync(this.alterName)
          .MapAsync(this.alterCountry)
          .MapAsync(this.applyMoreChange)
          .Map(this.mapper.map<ViewModel>);

since no user exists for userId 1, the GetUser(1) returns Option<None> and the remaining code fails with the exception

LangExt.ValueIsNoneException : Value is None.
at languageExt.OptionAsyncAwaiter`1.GetResult()

How to handle this case.? and to make sure the mapAsync and map chaining execute only if option is some user and not none.

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橘亓 2025-01-21 08:19:55

github 上的 This 页面似乎表明该选项将具有 .IfSome() 函数。 github 提供了以下代码片段：

// Returns the Some case 'as is' and 10 in the None case
int x = optional.IfNone(10);

// As above, but invokes a Func<T> to return a valid value for x
int x = optional.IfNone(() => GetAlternative());

// Invokes an Action<T> if in the Some state;
optional.IfSome(x => Console.WriteLine(x));

关于实施的建议（不知道项目的完整想法）将是这样的：

public async Task<Option<UserViewModel>> GetUser(int num)
{
    var user = await GetUser(1);
    if (user.IsSome)
    {
        user.MapAsync(this.alterName)
            .MapAsync(this.alterCountry)
            .MapAsync(this.applyMoreChange)
            .Map(this.mapper.map<ViewModel>);

        return user;
    }
}

This page on github seems to indicate that option will have a .IfSome() function. The github gives the following code snippet:

// Returns the Some case 'as is' and 10 in the None case
int x = optional.IfNone(10);

// As above, but invokes a Func<T> to return a valid value for x
int x = optional.IfNone(() => GetAlternative());

// Invokes an Action<T> if in the Some state;
optional.IfSome(x => Console.WriteLine(x));

A suggestion on implementation (without knowing the full idea of your project) would be something like this:

public async Task<Option<UserViewModel>> GetUser(int num)
{
    var user = await GetUser(1);
    if (user.IsSome)
    {
        user.MapAsync(this.alterName)
            .MapAsync(this.alterCountry)
            .MapAsync(this.applyMoreChange)
            .Map(this.mapper.map<ViewModel>);

        return user;
    }
}

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