Polly中调用异步方法的方式

最近在看Refit，一个还不错的REST API调用类库（我调用的API也无非是简单的增删改查），因为删除的时候会存在ID不存在的情况，所以就在调用的时候加入了Polly来进行删除的异常处理。

先来看一下后台的API代码

[Produces("application/json")]
[Route("api/Author")]
[ApiExplorerSettings(GroupName = "v1")]
public class AuthorController : Controller
{
    private readonly SwaggerDemoContext _swaggerDemoContext;

    public AuthorController(SwaggerDemoContext swaggerDemoContext)
    {
        _swaggerDemoContext = swaggerDemoContext;
    }

    // GET api/values
    [HttpGet]
    public IEnumerable<Author> Get()
    {
        var authors = _swaggerDemoContext.Authors.ToList();
        return authors;
    }

    // GET api/values/5
    [HttpGet("{id}")]
    public Author Get([FromRoute]int id)
    {
        var author = _swaggerDemoContext.Authors.Find(id);
        return author;
    }

    // POST api/values
    [HttpPost]
    public void Post([FromBody] Author author)
    {
        _swaggerDemoContext.Authors.Add(author);
        _swaggerDemoContext.SaveChanges();
    }

    // PUT api/values/5
    [HttpPut("{id}")]
    public void Put([FromRoute]int id, [FromBody] Author author)
    {
        author.Id = id;
        _swaggerDemoContext.Authors.Update(author);
        _swaggerDemoContext.SaveChanges();
    }

    // DELETE api/values/5
    [HttpDelete("{id}")]
    public void Delete([FromRoute]int id)
    {
        var author = _swaggerDemoContext.Authors.Find(id);
        _swaggerDemoContext.Authors.Remove(author);
        _swaggerDemoContext.SaveChanges();
    }
}

Refti的接口调用接口代码

public interface IAuthorApi
{
    [Get("/api/Author")]
    Task<IEnumerable<Author>> GetAuthors();

    [Get("/api/Author/{id}")]
    Task<Author> GetAuthor(int id);

    [Post("/api/Author")]
    Task PostAuthor([Body]Author author);

    [Put("/api/Author/{id}")]
    Task PutAuthor(int id, [Body]Author author);

    [Delete("/api/Author/{id}")]
    Task DeleteAuthor(int id);
}

在调用接口的时候Polly始终不能正确的抓取并处理异常，Polly处理部分代码如下：

private async static void foo()
{
    var authorApi = RestService.For<IAuthorApi>("http://localhost:8794");

    var delId = 2;
    await Policy
        .Handle<ApiException>()
        .RetryForever(ex =>
        {
          delId++;
        })
        .Execute(() => authorApi.DeleteAuthor(delId));
}

其中想要的是Id不存在（删除异常）时继续删除删除下一个Id，运行时Polly并不能正确的进行处理

unhandled exception.png

解决方法

Polly中调用异步方法要使用ExecuteAsync而不是Execute，同时需要修改处理方法为Async，代码修改如下：

await Policy
    .Handle<ApiException>()
    .RetryForeverAsync((ex, count) =>
    {
        delId++;
    })
    .ExecuteAsync(() => authorApi.DeleteAuthor(delId));

可以正常运行

success.png

后记

Polly对异步方法的支持点击查看
WebApi项目地址
调用客户端项目地址