数据异步

写了这么多年的程序，相信大家都知道连接数据库少不了这几个对象，DbConnection，DbCommand，DbDataReader等等。。先来看看ContinueWith在连接数据库时嵌套过深的尴尬。

当年异步和并发编程概念特别火，火热度参考现在的直播带货，这个时期的C#率先使用新的Task一网兜，在数据库操作的几大类中开始有了Async结尾的方法，如OpenAsync,ExecuteScalarAsync,ReadAsync 等等

1.DB NetFramework 4.5 下 await,async的写法

public static async Task<int> AsyncGetCount()
        {
            using (var connection = new MySqlConnection("server=xxx.xxx.xxx.xxx;userid=xxx;password=xxx;database=xxx;charset=utf8;port=3306;"))
            {
                await connection.OpenAsync();
                using (var command = connection.CreateCommand())
                {
                    command.CommandText = "select count(1) from messages";

                    var count = await command.ExecuteScalarAsync();

                    Console.WriteLine($"记录条数:{count}");

                    return Convert.ToInt32(count);
                }
            }
        }

-------- output -------------

记录条数:75896        

循环写法

public static async Task<List<string>> AsyncGetMessageList()
        {
            var messageList = new List<string>();
            using (var connection = new MySqlConnection("server=xxx.xxx.xxx.xxx;userid=xxx;password=xxx;database=xxx;charset=utf8;port=3306;"))
            {
                await connection.OpenAsync();
                using (var command = connection.CreateCommand())
                {
                    command.CommandText = "select message from messages limit 5;";
                    using (var reader = await command.ExecuteReaderAsync())
                    {
                        while (await reader.ReadAsync())
                        {
                            messageList.Add(reader["message"].ToString());
                        }
                    }
                }
            }
            return messageList;
        }

------------ output ----------------
你需要忘记失去的，感激拥有的，和期待将至的。
以前的找不到了。
对于编译错误，删除Pods文件夹然后重新pod install已经成为经验。次。
Hello，Is there anyone here?
放松心情

　　https://www.cnblogs.com/huangxincheng/p/12752849.html

并行编程中将lock锁次数降到最低实现无锁编程

var all = filterItemList.AsParallel().Select(m => GetCustomerIDList(m)).WithDegreeOfParallelism(2).ToList();
IEnumerable<int> final = all[0];
all.ForEach(m => final = final.Intersect(m));

　　

public static async Task<List<string>> AsyncGetMessageList()
        {
            var messageList = new List<string>();
            using (var connection = new MySqlConnection("server=xxx.xxx.xxx.xxx;userid=xxx;password=xxx;database=xxx;charset=utf8;port=3306;"))
            {
                await connection.OpenAsync();
                using (var command = connection.CreateCommand())
                {
                    command.CommandText = "select message from messages limit 5;";
                    using (var reader = await command.ExecuteReaderAsync())
                    {
                        while (await reader.ReadAsync())
                        {
                            messageList.Add(reader["message"].ToString());
                        }
                    }
                }
            }
            return messageList;
        }

------------ output ----------------
你需要忘记失去的，感激拥有的，和期待将至的。
以前的找不到了。
对于编译错误，删除Pods文件夹然后重新pod install已经成为经验。次。
Hello，Is there anyone here?
放松心情

　　

publicstatic async Task<int> AsyncGetCount() { using (var connection = new MySqlConnection("server=xxx.xxx.xxx.xxx;userid=xxx;password=xxx;database=xxx;charset=utf8;port=3306;")) { await connection.OpenAsync(); using (var command = connection.CreateCommand()) { command.CommandText = "select count(1) from messages"; var count = await command.ExecuteScalarAsync(); Console.WriteLine($"记录条数:{count}"); return Convert.ToInt32(count); } } } -------- output ------------- 记录条数:75896