ActionResult< IEnumerable< T>必须返回List< T>. [英] ActionResult<IEnumerable<T>> has to return a List<T>

问题描述

使用ASP.NET Core 2.1进行以下代码:

Take the following code using ASP.NET Core 2.1:

[HttpGet("/unresolved")]
public async Task<ActionResult<IEnumerable<UnresolvedIdentity>>> GetUnresolvedIdentities()
{
   var results = await _identities.GetUnresolvedIdentities().ConfigureAwait(false);
   return results.ToList();
}

自GetUnresolvedIdentities()返回IEnumerable<UnresolvedIdentity>以来，我一直以为我可以返回

I would have thought since GetUnresolvedIdentities() returns IEnumerable<UnresolvedIdentity> that I could just return

return await _identities.GetUnresolvedIdentities().ConfigureAwait(false);

除了我不能，因为出现此错误:

Except I can't, as I get this error:

CS0029无法隐式转换类型 'System.Collections.Generic.IEnumerable<Data.Infrastructure.Models.UnresolvedIdentity>' 到 'Microsoft.AspNetCore.Mvc.ActionResult<System.Collections.Generic.IEnumerable<Data.Infrastructure.Models.UnresolvedIdentity>>'

CS0029 Cannot implicitly convert type 'System.Collections.Generic.IEnumerable<Data.Infrastructure.Models.UnresolvedIdentity>' to 'Microsoft.AspNetCore.Mvc.ActionResult<System.Collections.Generic.IEnumerable<Data.Infrastructure.Models.UnresolvedIdentity>>'

我需要.ToList()，这很烦人，因为它是2行而不是1行.

I need the .ToList(), which is annoying as it's 2 lines rather than 1.

为什么ActionResult<T>不能弄清楚GetUnresolvedIdentities()返回一个IEnumerable<>而仅仅返回它呢?

Why can't ActionResult<T> figure out that GetUnresolvedIdentities() returns an IEnumerable<> and just return that?

GetUnresolvedIdentities的签名是:

Task<IEnumerable<UnresolvedIdentity>> GetUnresolvedIdentities();

推荐答案

从msdn中获取此文档: https ://docs.microsoft.com/zh-cn/aspnet/core/web-api/action-return-types?view = aspnetcore-2.1#actionresultt-type

Take this documentation from msdn: https://docs.microsoft.com/en-us/aspnet/core/web-api/action-return-types?view=aspnetcore-2.1#actionresultt-type

C#不支持接口上的隐式强制转换运算符. 因此，将接口转换为具体类型是 必须使用ActionResult<T>.

C# doesn't support implicit cast operators on interfaces. Consequently, conversion of the interface to a concrete type is necessary to use ActionResult<T>.

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