C# foreach遇到async和await

Posted 2021-11-23 sea1ee

一个简单的列子，需要把一个集合的数据添加到数据库中。

我先这样写了，然后报错了

     public async Task<IHttpActionResult> Test([FromUri]string name = "")
        {
            List<string> strList = new List<string>() { "测试", "测试1", "测试2", "测试3", "测试4", "测试5", "测试6", "测试7", "测试8" };
            strList.ForEach(async x =>
            {
                JkSystemname jk = await dbOracle.JkSystemnames.AsQueryable().FirstAsync(ee => ee.Name == x);
                if (jk == null)
                {
                    jk = new JkSystemname() { Name = x };
                    dbOracle.JkSystemnames.Insert(jk);
                }
            });
            return await Task.FromResult(Ok(new { errcode = 0, errmag = "success" }));
        }

 

两个办法解决循环里面不能使用异步

①把方法提出来，然后返回task，然后一起执行，这样不会按顺序执行

 public async Task<IHttpActionResult> Test([FromUri]string name = "")
        {
            List<string> strList = new List<string>() { "测试", "测试1", "测试2", "测试3", "测试4", "测试5", "测试6", "测试7", "测试8" };
            IEnumerable<Task> tasks = strList.Select(x => TestAsync(x));//映射到一个可以遍历的task
            await Task.WhenAll(tasks);  //使用task.whenall 完成
            return await Task.FromResult(Ok(new { errcode = 0, errmag = "success" }));
        }

        /// <summary>
        /// 根据传入的名称，返回需要执行的task代码
        /// </summary>
        /// <param name="name"></param>
        /// <returns></returns>
        public async Task TestAsync(string name)
        {
            JkSystemname jk = await dbOracle.JkSystemnames.AsQueryable().FirstAsync(ee => ee.Name == name);
            if (jk == null)
            {
                jk = new JkSystemname() { Name = name };
                dbOracle.JkSystemnames.Insert(jk);
            }
        }

 

 

 

②扩展方法，一个个的执行

 /// <summary>
        /// 使用异步遍历处理数据
        /// </summary>
        /// <typeparam name="T">需要遍历的基类</typeparam>
        /// <param name="list">集合</param>
        /// <param name="func">Lambda表达式</param>
        /// <returns></returns>
        public static async Task ForEachAsync<T>(this List<T> list, Func<T, Task> func)
        {
            foreach (T value in list)
            {
                await func(value);
            }
        }

 public async Task<IHttpActionResult> Test([FromUri]string name = "")
        {
            List<string> strList = new List<string>() { "测试", "测试1", "测试2", "测试3", "测试4", "测试5", "测试6", "测试7", "测试8" };
            //①先得到集合，然后一起执行
            //IEnumerable<Task> tasks = strList.Select(x => TestAsync(x));//映射到一个可以遍历的task
            //await Task.WhenAll(tasks);  //使用task.whenall 完成
            //②一步一步的循环
            await strList.ForEachAsync<string>(async x =>
            {
                JkSystemname jk = await dbOracle.JkSystemnames.AsQueryable().FirstAsync(ee => ee.Name == x);
                if (jk == null)
                {
                    jk = new JkSystemname() { Name = x };
                    dbOracle.JkSystemnames.Insert(jk);
                }
            });
           
            return await Task.FromResult(Ok(new { errcode = 0, errmag = "success" }));
        }