C# - "Connection must be valid and open" 具有多个查询和方法 |连接未关闭？

Question

现在很多小时了，无论我做了什么改变，我都因为同样的错误而失去了它。我正在尝试制作一个命令行应用程序，它将根据两个参数输入 modname 和可选的 author 从数据库中检索信息。查询都在 jobs.cs 文件中处理。入口点文件调用方法 beginJob() 获取目标 modname 和 author（如果指定）进行查询。与我在这里阅读的大约一百个其他 post 不同的是，发出的第一个查询完全正常，而且我肯定会关闭 reader 和连接。（不会在生产中每次都关闭连接，但我在这里是出于调试目的）。下次我调用连接时会导致此错误。

System.InvalidOperationException: Connection must be valid and open.
   at MySql.Data.MySqlClient.ExceptionInterceptor.Throw(Exception exception)
   at MySql.Data.MySqlClient.MySqlConnection.Throw(Exception ex)
   at MySql.Data.MySqlClient.MySqlCommand.CheckState()
   at MySql.Data.MySqlClient.MySqlCommand.ExecuteReader(CommandBehavior behavior)
   at MySql.Data.MySqlClient.MySqlCommand.ExecuteReader()
   at vmcmod.Job.queryAuthor(String authorUID) in F:\Projects\VisualStudio\VMC-MOD\vmcmod\job.cs:line 235
   at vmcmod.Job.StartJob() in F:\Projects\VisualStudio\VMC-MOD\vmcmod\job.cs:line 47
   at vmcmod.Job.queryModAndAuthor(String modname, String author) in F:\Projects\VisualStudio\VMC-MOD\vmcmod\job.cs:line 205
   at vmcmod.Job.beginJob() in F:\Projects\VisualStudio\VMC-MOD\vmcmod\job.cs:line 27
   at vmcmod.VMCMOD.parseArgs() in F:\Projects\VisualStudio\VMC-MOD\vmcmod\vmcmod.cs:line 58

一些 post 我看过但似乎没有帮助：

Connection must be valid and open error
C# Query: 'System.InvalidOperationException' | Additional information: Connection must be valid and open

C# 源文件（请尝试，不要太紧张，这是我的第一个 C# 应用程序）：

jobs.cs[更新]

using MySql.Data.MySqlClient;
using System;

namespace vmcmod
{
    class Job
    {
        public bool checkInput()
        {
            if (Global.currentJobTargetModname == "undefined")
            {
                Utils.consoleLog("The mod name is required.", 3);
                return false;
            }
            else
            {
                return true;
            }
        }
        public void beginJob()
        {
            string targetModname = Global.currentJobTargetModname.ToLower();
            string targetModAuthor = Global.currentJobTargetAuthor.ToLower();
            if (targetModAuthor != "undefined")
            {
                queryModAndAuthor(targetModname, targetModAuthor);
                Utils.consoleLog("Job Call. (Author defined)", 4);
            }
            else
            {
                queryMod(targetModname);
                Utils.consoleLog("Job Call. (Author undefined)", 4);
            }
        }
        private void StartJob()
        {
            string author = null;
            string targetModAuthor = Global.currentJobTargetAuthor.ToLower();
            Utils.consoleLog("Mod exists.", 5);
            if (targetModAuthor == "undefined")
            {
                author = "(None; First in row)";
            }
            else
            {
                queryAuthor(Global.queryResModAuthorID);
                author = "'" + Global.queryResModAuthor + "' (UUID:" + Global.queryResModAuthorID + ") ";
            }
            var collaborators_obj = Newtonsoft.Json.Linq.JObject.Parse(Global.queryResModCollab);
            var tags_obj = Newtonsoft.Json.Linq.JObject.Parse(Global.queryResModTags);
            Console.BackgroundColor = ConsoleColor.Blue;
            Console.ForegroundColor = ConsoleColor.White;
            Console.WriteLine("MOD INSTALL SPECIFICATIONS:");
            Console.BackgroundColor = ConsoleColor.Black;
            Console.WriteLine("     Mod Name: '" + Global.queryResModName + "'");
            Console.Write("     Mod Author: " + author);
            if (Global.queryResModAuthorVerified == true && targetModAuthor != "undefined")
            {
                Utils.consoleTag("*VERIFIED*", ConsoleColor.Green);
            }
            if (Global.queryResModAuthorVerified == false && targetModAuthor != "undefined")
            {
                Utils.consoleTag("*UNVERIFIED*", ConsoleColor.Red);
            }
            Console.Write("\n");
            Console.WriteLine("     Mod Version: " + Global.queryResModVersion);
            Console.WriteLine("     Installations: " + Global.queryResModInstalls);
            Console.WriteLine("     Description:\n      " + Global.queryResDescription);
            Console.WriteLine("     Mod UUID: " + Global.queryResModUid);
            if (Global.advInfo == true)
            {
                Console.WriteLine("     Rep. Entry #" + Global.queryResModID);
                Console.WriteLine("     Mod Created On: " + Utils.UnixTimeStampToDateTime(Convert.ToDouble(Global.queryResDateCreated)));
                Console.WriteLine("     Mod Last Modified On: " + Utils.UnixTimeStampToDateTime(Convert.ToDouble(Global.queryResDateLastModf)));
                Console.WriteLine("     Tags: \n        " + Convert.ToString(tags_obj["tags"]));
                Console.WriteLine("     Collaborators: \n       " + Convert.ToString(collaborators_obj["collaborators"]));
            }
            Utils.consoleSeparator();
            bool user_response = Utils.consoleAskYN("Are you sure you want to install this mod?");
            if (user_response == true)
            {
                queryGetModJSON(Global.queryResModUid);
                Utils.consoleLog("JSON Data: "+Global.queryResModJSON,5);
                //FileIO fio = new FileIO();
                //fio.jsonToFiles(fio.jsonToArray(Global.queryResModJSON));
            }
            else
            {
                Utils.consoleSetKeyExit();
            }
        }
        private void queryGetModJSON(string uuid)
        {
            var dbCon = new DBConnection();
            if (dbCon.IsConnect() == false)
            {
                Utils.consoleLog("Unable to query repository or no results.", 3);
                Utils.consoleSetKeyExit();
            }
            else
            {
                string q = "SELECT data_json FROM vmcmod_repository_data WHERE uid='" + uuid + "' LIMIT 1;";
                MySqlCommand cmd = new MySqlCommand(q, dbCon.Connection);
                var reader = cmd.ExecuteReader();
                if (!reader.HasRows)
                {
                    Utils.consoleLog("Mod data not found.", 3);
                    reader.Close();
                    dbCon.Close();
                }
                else
                {
                    while (reader.Read())
                    {
                        Global.queryResModJSON = reader.GetString(0);
                    }
                    reader.Close();
                    dbCon.Close();
                }
            }
        }
        private void queryMod(string modname)
        {
            var dbCon = new DBConnection();
            if (dbCon.IsConnect() == false)
            {
                Utils.consoleLog("Unable to query repository or no results.", 3);
                Utils.consoleSetKeyExit();
            }
            else
            {
                string q = "SELECT id,uid,author_id,mod_name,status,dependencies_json,description,mod_version,date_created,date_last_modified,collaborators,tags_json,installs FROM vmcmod_repository_info WHERE mod_name LIKE'" + modname + "' LIMIT 1;";
                MySqlCommand cmd = new MySqlCommand(q, dbCon.Connection);
                var reader = cmd.ExecuteReader();
                if (!reader.HasRows)
                {
                    Utils.consoleLog("Mod not found.", 3);
                    reader.Close();
                    dbCon.Close();
                }
                else
                {
                    while (reader.Read())
                    {
                        Global.queryResModInstalls = reader.GetInt32(12);
                        Global.queryResModTags = reader.GetString(11);
                        Global.queryResModCollab = reader.GetString(10);
                        Global.queryResDateLastModf = reader.GetInt32(9);
                        Global.queryResDateCreated = reader.GetInt32(8);
                        Global.queryResModVersion = reader.GetFloat(7);
                        Global.queryResDescription = reader.GetString(6);
                        Global.queryResModDependencies = reader.GetString(5);
                        Global.queryResModStatus = reader.GetInt16(4);
                        Global.queryResModName = reader.GetString(3);
                        Global.queryResModAuthorID = reader.GetString(2);
                        Global.queryResModUid = reader.GetString(1);
                        Global.queryResModID = Convert.ToInt32(reader.GetInt32(0));
                    }
                    reader.Close();
                    dbCon.Close();
                    StartJob();
                }
            }
        }
        private void queryModAndAuthor(string modname, string author)
        {
            var dbCon = new DBConnection();
            if (dbCon.IsConnect() == false)
            {
                Utils.consoleLog("Unable to query repository or no results.", 3);
                Utils.consoleSetKeyExit();
            }
            else
            {
                string q = "SELECT id,uid,author_id,mod_name,status,dependencies_json,description,mod_version,date_created,date_last_modified,collaborators,tags_json,installs FROM vmcmod_repository_info WHERE mod_name LIKE'" + modname + "' LIMIT 1;";
                MySqlCommand cmd = new MySqlCommand(q, dbCon.Connection);
                var reader = cmd.ExecuteReader();
                if (!reader.HasRows)
                {
                    Utils.consoleLog("Mod not found.", 3);
                    reader.Close();
                    dbCon.Close();
                }
                else
                {
                    while (reader.Read())
                    {
                        Global.queryResModInstalls = reader.GetInt32(12);
                        Global.queryResModTags = reader.GetString(11);
                        Global.queryResModCollab = reader.GetString(10);
                        Global.queryResDateLastModf = reader.GetInt32(9);
                        Global.queryResDateCreated = reader.GetInt32(8);
                        Global.queryResModVersion = reader.GetFloat(7);
                        Global.queryResDescription = reader.GetString(6);
                        Global.queryResModDependencies = reader.GetString(5);
                        Global.queryResModStatus = reader.GetInt16(4);
                        Global.queryResModName = reader.GetString(3);
                        Global.queryResModAuthorID = reader.GetString(2);
                        Global.queryResModUid = reader.GetString(1);
                        Global.queryResModID = Convert.ToInt32(reader.GetInt32(0));
                    }
                    reader.Close();
                    dbCon.Close();
                    StartJob();
                }
            }
        }
        private bool queryCheckAuthorExists(string author)
        {
            var dbCon = new DBConnection();
            string q = "SELECT * FROM vmcmod_users WHERE username='"+author+ "' AND is_author=true LIMIT 1;";
            MySqlCommand cmd = new MySqlCommand(q, dbCon.Connection);
            var reader = cmd.ExecuteReader();
            if (reader.HasRows == false)
            {
                Utils.consoleLog("Author not found.", 3);
                reader.Close();
                dbCon.Close();
                return false;
            }
            else
            {
                Utils.consoleLog("Author found.", 4);
                reader.Close();
                dbCon.Close();
                return true;
            }
        }
        private void queryAuthor(string authorUID)
        {
            var dbCon = new DBConnection();
            string q = "SELECT username,is_verified_user FROM vmcmod_users WHERE uid='" + authorUID + "' AND is_author=true LIMIT 1;";
            MySqlCommand cmd = new MySqlCommand(q, dbCon.Connection);
            var reader = cmd.ExecuteReader();
            if (reader.HasRows == false)
            {
                Utils.consoleLog("Author not found.", 3);
                reader.Close();
                dbCon.Close();
            }
            else
            {
                while (reader.Read())
                {
                    Global.queryResModAuthor = reader.GetString(0);
                    Global.queryResModAuthorVerified = reader.GetBoolean(1);
                }
                Utils.consoleLog("Author found.", 4);
                reader.Close();
                dbCon.Close();
            }
        }
    }
}

dbinterface.cs（这不是我写的，而是从 Whosebug 上的 post 获取和编辑的，here）[更新]

using MySql.Data.MySqlClient;
using System;

namespace vmcmod
{
    public class DBConnection
    {
        public DBConnection()
        {
        }

        public string Password { get; set; }
        private MySqlConnection connection = null;
        public MySqlConnection Connection
        {
            get { return connection; }
        }

        public bool IsConnect()
        {
            bool result = true;
            if (Connection == null)
            {
                string connString = "Server=...; Port=...; Database=...; Uid=...; Pwd=...;";
                connection = new MySqlConnection(connString);
                try
                {
                    connection.Open();
                    Utils.consoleLog("Connected to repository.", 4);
                    result = true;
                }
                catch (Exception e)
                {
                    Utils.consoleLog("Error occured while connecting to repository.", 3);
                    Utils.consoleLog("MySQL Exception: "+e,5);
                    result = false;
                }
            }

            return result;
        }

        public void Close()
        {
            connection.Close();
            connection = null;
        }
    }
}

global.cs（全局变量存储）

using System;

namespace vmcmod
{
    class Global
    {
        internal const float version = 0.1F;
        internal static string currentJobWorld = "New World";
        internal static string currentJobTargetModname = "undefined";
        internal static string currentJobTargetAuthor = "undefined";
        internal static string currentJobProfile = "default";
        internal static int currentJobAccountPIN;
        internal static bool verbose = false;
        internal static bool debug = false;
        internal static bool advInfo = false;
        internal static bool queryResModAuthorVerified = false;
        internal static string queryResModUid;
        internal static string queryResModAuthorID;
        internal static string queryResModAuthor;
        internal static string queryResModName;
        internal static string queryResModDependencies = "{\"dependencies\":[]}";
        internal static int queryResModStatus;
        internal static float queryResModVersion;
        internal static string queryResDescription = "None provided.";
        internal static int queryResDateCreated;
        internal static int queryResDateLastModf;
        internal static int queryResModID;
        internal static string queryResModCollab = "{\"collaborators\":[]}";
        internal static string queryResModTags = "{\"tags\":[]}";
        internal static int queryResModInstalls;
        internal static string queryResModJSON = "{}";
    }
}

Answer 1

快速而肮脏的解决方案是更改：

    public void Close()
    {
        connection.Close();
    }

至：

    public void Close()
    {
        connection.Close();
        connection = null;
    }

此外，删除此代码：

    private static DBConnection _instance = null;
    public static DBConnection Instance()
    {
        if (_instance == null)
            _instance = new DBConnection();
        return _instance;
    }

而不是使用 DBConnection.Instance，只需使用 new DBConnection();

并更改：

    public MySqlConnection Connection
    {
        get { return connection; }
    }

至：

    public MySqlConnection Connection
    {
        get {
            IsConnect();
            return connection; }
    }

并更改：

    public bool IsConnect()
    {
        bool result = true;
        if (Connection == null)

至：

    public bool IsConnect()
    {
        bool result = true;
        if (connection == null)

Answer 2

我看到您正在为 DBConnection 使用单态模式，这不是一个好主意。

private static DBConnection _instance = null;
    public static DBConnection Instance()
    {
        if (_instance == null)
            _instance = new DBConnection();
        return _instance;
    }

您可能想查看此答案以获取更多信息：

Answer 3

根据@mjwills 的回复，我刷过的数据库接口脚本非常古怪，一次只允许一个实例。

工作数据库接口

using MySql.Data.MySqlClient;
using System;

namespace vmcmod
{
    public class DBConnection
    {
        public DBConnection()
        {
        }
        public string Password { get; set; }
        private MySqlConnection connection = null;
        public MySqlConnection Connection
        {
            get
            {
                IsConnect();
                return connection;
            }
        }
        public bool IsConnect()
        {
            bool result = true;
            if (connection == null)
            {
                string connString = "Server=...; Port=...; Database=...; Uid=...; Pwd=...;";
                connection = new MySqlConnection(connString);
                try
                {
                    connection.Open();
                    Utils.consoleLog("Connected to repository.", 4);
                    result = true;
                }
                catch (Exception e)
                {
                    Utils.consoleLog("Error occured while connecting to repository.", 3);
                    Utils.consoleLog("MySQL Exception: "+e,5);
                    result = false;
                }
            }

            return result;
        }

        public void Close()
        {
            connection.Close();
            connection = null;
        }
    }
}

C# - "Connection must be valid and open" 具有多个查询和方法 |连接未关闭？

C# - "Connection must be valid and open" with multiple Queries and Methods | Connection not closed?

c#

mysql

database-connection