C# foreach遇到async和await

2021-06-10 02:04

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标签：names info stat sel img 集合 lam type color

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 Test([FromUri]string name = "")
        {
            Liststring> strList = new Liststring>() { "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" }));
        }

技术图片

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 Test([FromUri]string name = "")
        {
            Liststring> strList = new Liststring>() { "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 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" }));
        }

        /// 
        /// 根据传入的名称，返回需要执行的task代码
        /// 
        /// 
        /// 
        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);
            }
        }

技术图片

②扩展方法，一个个的执行

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

 public async Task Test([FromUri]string name = "")
        {
            Liststring> strList = new Liststring>() { "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 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.ForEachAsyncstring>(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" }));
        }