Question

我试图弄清楚如何在ASP.NET C＃中使用MySql In cluse。这是我的代码

var WebSites = string.Join(",", wsl.Select(x => "'" + x.DomainUrl + "'").ToArray());
string q = "select Id, Url, Title, Date, ImageUrl from post where WebSiteUrl IN (@Url)";

当我不使用参数时，此代码有效。当我包含参数时，我得不到查询的结果。

这是我的参数代码

cmd.Parameters.Add("@Urls", MySqlDbType.Text).Value = WebSites;

这里是整个代码

 public static IList<Post> FindPostsByWebSiteList(IEnumerable<WebSite> wsl)
 {
        var pl = new List<Post>();
        var WebSites = string.Join(",", wsl.Select(x => "'" + x.DomainUrl + "'").ToArray());
        string q = "select Id, Url, Title, Date, ImageUrl from post where WebSiteUrl IN (@Urls)";

        using (MySqlConnection con = new MySqlConnection(WebConfigurationManager.ConnectionStrings["MySqlConnectionString"].ToString()))
        {
            using (MySqlCommand cmd = new MySqlCommand(q, con))
            {
                cmd.Parameters.Add("@Urls", MySqlDbType.Text).Value = WebSites;
                con.Open();

                var reader = cmd.ExecuteReader(CommandBehavior.CloseConnection);
                while (reader.Read())
                {
                    var p = new Post();
                    p.Id = reader.GetInt32("Id");
                    p.Url = reader.GetString("Url");
                    p.Title = reader.GetString("Title");
                    p.Date = reader.GetDateTime("Date");
                    p.ImageUrl = reader.GetString("ImageUrl");
                    pl.Add(p);
                }
                return pl;
            }
        }
    }

Answer 1

您引用了@Url而不是@Urls

可能只是你问题中的拼写错误

Answer 2

我找到了答案。这是

    public static IList<Post> FindPostsByWebSiteList(string[] urls)
    {
        var pl = new List<Post>();
        var urlArray = urls.Select((x,y) => "@url" + y.ToString()).ToArray();
        var urlsJoined = string.Join(",", urlArray);
        string q = string.Format("select Id, Url, Title, Date, ImageUrl from post where WebSiteUrl IN ({0})", urlsJoined);

        using (MySqlConnection con = new MySqlConnection(WebConfigurationManager.ConnectionStrings["MySqlConnectionString"].ToString()))
        {
            using (MySqlCommand cmd = new MySqlCommand(q, con))
            {
                for (int x = 0; x < urlArray.Length; x++)
                {
                    cmd.Parameters.Add(urlArray[x], MySqlDbType.Text).Value = urls[x];
                }

                con.Open();

                var reader = cmd.ExecuteReader(CommandBehavior.CloseConnection);
                while (reader.Read())
                {
                    var p = new Post();
                    p.Id = reader.GetInt32("Id");
                    p.Url = reader.GetString("Url");
                    p.Title = reader.GetString("Title");
                    p.Date = reader.GetDateTime("Date");
                    p.ImageUrl = reader.GetString("ImageUrl");
                    pl.Add(p);
                }
                return pl;
            }
        }
    }

Answer 3

IN语句应该是一个字符串数组，并且您传递的是一个字符串

您的最终SQL看起来像这样：

select Id, Url, Title, Date, ImageUrl from post where WebSiteUrl IN ('url1,url2,url3')

而不是

select Id, Url, Title, Date, ImageUrl from post where WebSiteUrl IN ('url1', 'url2', 'url3')

检查此问题：

Add List<int> to a mysql parameter

你如何使用MySql IN子句

3 个答案: