JSON值无法转换为System.Nullable [System.Int32] [英] The JSON value could not be converted to System.Nullable[System.Int32]

问题描述

我将ASP.NET Core 2.2 API更新为ASP.NET Core 3.0，并且正在使用System.Json:

I updated an ASP.NET Core 2.2 API to ASP.NET Core 3.0 and I am using System.Json:

services
  .AddMvc()
  .SetCompatibilityVersion(CompatibilityVersion.Version_3_0)
  .AddJsonOptions(x => {}) 

然后，我尝试使用以前使用过的Angular 8发布JSON数据:

I then tried to post JSON data using Angular 8, which was working before:

{
  "name": "John"
  "userId": "1"
}

ASP.NET Core 3.0 API中的模型是:

The model in the ASP.NET Core 3.0 API is:

public class UserModel {
  public String Name { get; set; }
  public Int32? UserId { get; set; } 
}

API Controller的操作如下:

And the API Controller action is as follows:

[HttpPost("users")]
public async Task<IActionResult> Create([FromBody]PostModel) { 
}

提交模型时，出现以下错误:

When I submit the model I get the following error:

The JSON value could not be converted to System.Nullable[System.Int32]. 

使用System.Json代替Newtonsoft时是否需要做其他事情?

Do I need to do something else when using System.Json instead of Newtonsoft?

推荐答案

在这里，通过json，您传递了UserId的字符串值，但是您的模型引用了int32?UserId的值.那么您的值如何从字符串转换为int32?

Here Via the json you pass a string value for UserId but your model refer a int32? value for UserId. Then how your value convert from string to int32?

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