c# - 异步 Web API 端点

Question

以下 Web API 端点仍然出现以下错误:

"A second operation started on this context before a previous asynchronous operation completed."

由于我将 .ToListAsync 与从 Entity Framework 返回的数据一起使用，我假设问题出在 var user 行阻塞。

如何使该部分也异步？

[Route("Retailers/{search}")]
[HttpGet]
public Task<List<Lookup>> Retailers(string search)
{
    var user = UserManager.FindById(User.Identity.GetUserId());
    Guid userId = Guid.Parse(user.Id);

    var companies = _unitOfWork.GetRepository<Company>().GetAll().Where(c => c.CompanyType == CompanyType.Retail && 
                (c.UserID == null || c.UserID == userId) && c.CompanyName.StartsWith(search)).Take(5)
                .Select(x => new Lookup { Id = x.Id, Name = x.CompanyName }).ToListAsync();

    return companies;
}

Answer 1

您缺少 async 和 await 关键字。

1. 将async 添加到方法签名中。
2. 将 await 添加到对 _unitOfWork.GetRepository...ToListAsync() 的调用中

代码:

[Route("Retailers/{search}")]
[HttpGet]
public async Task<List<Lookup>> Retailers(string search)
{
    var user = UserManager.FindById(User.Identity.GetUserId());
    Guid userId = Guid.Parse(user.Id);

    var companies = await _unitOfWork.GetRepository<Company>().GetAll().Where(c => c.CompanyType == CompanyType.Retail && 
                (c.UserID == null || c.UserID == userId) && c.CompanyName.StartsWith(search)).Take(5)
                .Select(x => new Lookup { Id = x.Id, Name = x.CompanyName }).ToListAsync();

    return companies;
}

这里有一个很好的异步编程链接作为引用:Asynchronous Programming with Async and Await .