CORS来自一个组件的错误，而不是其他组件

Question

[我有一个使用React 16的.NET Core 3.1.3应用程序，当我在生产环境（Azure / Firebase）中调用API时，从一个特定组件收到CORS错误。

在大多数应用程序中，一切正常，所有axios调用的基本URL都设置在一个文件中，所有发布请求都通过rootHttp类的单个方法进行。

    addItem(model, data){
      return axios.post(
          this.rootUrl + '/' + model, data, {headers: this.headers}
      );
    }
    //Posts new item to API

除了来自employee组件的POST调用之外，所有的API调用似乎都运行良好：

export function addEmployee(employee, callback){
    employee = prepEmployeeValues(employee);
    return dispatch =>{
        http.addItem("employee", employee)
            .then(addedEmployee =>{
                dispatch(addEmployeeToState(addedEmployee.data));
                callback();
            });
    }
}
//Posts new employee to API

哪个会触发这两个错误：

Access to XMLHttpRequest at 'https://procmanagement.azurewebsites.net/api/3/employee' 
    from origin 'https://scheduleanddirection.firebaseapp.com' 
    has been blocked by CORS policy: No 'Access-Control-Allow-Origin' 
    header is present on the requested resource.

和

createError.js:16 Uncaught (in promise) Error: Network Error
    at e.exports (createError.js:16)
    at XMLHttpRequest.p.onerror (xhr.js:83)

请求标头与任何其他组件的成功POST调用相同。值得注意的是，来自Employee组件的GET返回一个空数组，并且最初应返回一个1 Employee Object的数组，该所有者是在注册帐户时添加的所有者（在dev服务器中有效）。

后端应在此处收到员工的职位：

        [HttpPost]
        public async Task<IActionResult> AddEmployee(int userId, EmployeeForCreationDto employeeForCreation)
        {
            EmployeeIdIncrement employeeIdIncrement = await _repo.GetEmployeeIdForIncrement(userId);
            employeeIdIncrement.employeeId = employeeIdIncrement.employeeId + 1;

            var creator = await _userRepo.GetUser(userId);

            if (creator.Id != int.Parse(User.FindFirst(ClaimTypes.NameIdentifier).Value))
                return Unauthorized();

            var employee = _mapper.Map<Employee>(employeeForCreation);

            employee.User = creator;

            employee.EmployeeId = employeeIdIncrement.employeeId;

            _repo.Add(employee);

            if (await _repo.SaveAll())
            {
                var employeeToReturn = _mapper.Map<EmployeeForReturnDto>(employee);
                return CreatedAtRoute("GetEmployee", new {employeeId = employee.EmployeeId, userId = userId }, employeeToReturn);
            }

            throw new Exception("Creation of Employee failed on save");

        }

一个成功的例子：

发送：

export function addDepartment(department, callback){
    department = prepDepartmentValues(department);
    return dispatch =>{
        http.addItem("department", department)
            .then(addedDepartment =>{
                dispatch(addDepartmentToState(addedDepartment.data));
                callback();
            });
    }
}
//Posts new department to API

接收：

        [HttpPost]
        public async Task<IActionResult> AddDepartment(int userId, DepartmentForCreationDto departmentForCreation)
        {
            var creator = await _userRepo.GetUser(userId);

            if (creator.Id != int.Parse(User.FindFirst(ClaimTypes.NameIdentifier).Value))
                return Unauthorized();

            var department = _mapper.Map<Department>(departmentForCreation);

            department.User = creator;

            _repo.Add(department);

            if (await _repo.SaveAll())
            {
                var jobToReturn = _mapper.Map<DepartmentForCreationDto>(department);
                return CreatedAtRoute("GetDepartment", new {deptName = department.DeptName, userId = userId }, jobToReturn);
            }

            throw new Exception("Creation of Department failed on save");

        }

包括Employee组件的所有组件在开发服务器中都可以正常工作，除了Employee组件之外的所有组件都可以在生产环境中工作。

CORS政策：

            services.AddCors(options =>
            {
                options.AddPolicy("ProdCors",
                    builder =>
                    {
                        builder.WithOrigins("https://scheduleanddirection.firebaseapp.com", "https://scheduleanddirection.web.app")
                            .AllowAnyMethod()
                            .AllowAnyHeader()
                            .AllowCredentials();
                    }
                );
            });

Answer 1

因此，经过深思熟虑之后，我发现实际上不是CORS问题导致了我这个错误。

我用Postman检查API，发现我遇到内部服务器错误，然后将我的Dev服务器API连接到生产数据库，在该数据库中，我发现问题是与SQLite相比，MS SQL Server的工作方式。

Dev服务器使用SQLite。 MS SQL Server在使用SQLite的两件事上遇到问题：

1. 未经明确许可，一次更新多个数据。通过在我的连接字符串中添加“ MultipleActiveResultSets = True”来解决此问题。

2. 用单个主键（而不是组合键）显式定义项目的主键。通过完全删除EmployeeIdForIncrement模型并添加EmployeeIdForIncrement作为用户模型的属性来解决此问题。