c＃ - 我如何检查用户（创建或不创建）

Question

我正在使用MySql 5.6。

using System; 
using System.Collections.Generic; 
using System.Text; 
using System.IO; 
using MySql.Data.MySqlClient; 

    namespace MySqlRank 
    { 
     class Sql 
     { 
      private MySqlConnection connection; 
      private string server; 
      private string database; 
      private string uid; 
      private string password; 

      //Constructor 
      public Sql() 
      { 
       Initialize(); 
      } 



      //Initialize values 
      private void Initialize() 
      { 
       server = "localhost"; 
       database = "db"; 
       uid = "root"; 
       password = "pass"; 
       string connectionString; 
       connectionString = "SERVER=" + server + ";" + "DATABASE=" + database + ";" + "UID=" + uid + ";" + "PASSWORD=" + password + ";"; 

       connection = new MySqlConnection(connectionString); 
      } 


      //open connection to database 
      private bool OpenConnection() 
      { 
       try 
       { 
        connection.Open(); 
        return true; 
       } 
       catch (MySqlException ex) 
       { 
        switch (ex.Number) 
        { 
         case 0: 
          Console.WriteLine("Cannot connect to server. Contact administrator"); 
          break; 

         case 1045: 
          Console.WriteLine("Invalid username/password, please try again"); 
          break; 
        } 
        return false; 
       } 
      } 

      private bool CloseConnection() 
      { 
       try 
       { 
        connection.Close(); 
        return true; 
       } 
       catch (MySqlException ex) 
       { 
        Console.WriteLine(ex.Message); 
        return false; 
       } 
      } 

      //Insert statement 
      public void Successful(ulong Id) 
      { 
       //if(NotCreated) 
       { 
        string query = "INSERT INTO rank(id, trades) VALUES('" + Id + "', '1')"; 

        //open connection 
        if (this.OpenConnection() == true) 
        { 
         //create command and assign the query and connection from the constructor 
         MySqlCommand cmd = new MySqlCommand(query, connection); 

         //Execute command 
         cmd.ExecuteNonQuery(); 

         //close connection 
         this.CloseConnection(); 
        } 
       }  
       //else if (created) 
       { 
        string query = "UPDATE rank SET trades='1' WHERE id='" + Id + "'"; 

        //Open connection 
        if (this.OpenConnection() == true) 
        { 
         MySqlCommand cmd = new MySqlCommand(); 
         cmd.CommandText = query; 
         cmd.Connection = connection; 

         //Execute query 
         cmd.ExecuteNonQuery(); 
         //close connection 
         this.CloseConnection(); 
        } 
       } 
      } 

      //Delete statement 
      public void Delete(ulong Id) 
      { 
       string query = "DELETE FROM rank WHERE id='"+ Id +"'"; 

       if (this.OpenConnection() == true) 
       { 
        MySqlCommand cmd = new MySqlCommand(query, connection); 
        cmd.ExecuteNonQuery(); 
        this.CloseConnection(); 
       } 
      } 

      //Select statement 
      public List<string>[] Select() 
      { 
       string query = "SELECT * FROM rank"; 

       //Create a list to store the result 
       List<string>[] list = new List<string>[3]; 
       list[0] = new List<string>(); 
       list[1] = new List<string>(); 

       //Open connection 
       if (this.OpenConnection() == true) 
       { 
        //Create Command 
        MySqlCommand cmd = new MySqlCommand(query, connection); 
        //Create a data reader and Execute the command 
        MySqlDataReader dataReader = cmd.ExecuteReader(); 

        //Read the data and store them in the list 
        while (dataReader.Read()) 
        { 
         list[0].Add(dataReader["id"] + ""); 
         list[1].Add(dataReader["trades"] + ""); 
        } 

        //close Data Reader 
        dataReader.Close(); 

        //close Connection 
        this.CloseConnection(); 

        //return list to be displayed 
        return list; 
       } 
       else 
       { 
        return list; 
       } 
      } 
     } 
    } 

我对成功的void.I问题试试，导管的方法，但，这是不行的。（ID是唯一的密钥）.Afaik我我需要选择的方法，但我can't.My表名rank（id，trade）。我需要创建更新交易+ 1.如果没有创建，创建一个新的用户。我只需要检查创建或不创建。

Answer 1

如果我理解你的问题正确，你想检查表中是否已经存在该行？如果是这样，你可以在主键冲突的catch语句检查：

catch(MySqlException ex) 
    { 
    this.CloseConnection(); 
    if(ex.Number == 1067) 
    { 
    //Handle exception 
    } 
    } 

编辑：我自己的机器上测试代码后，我发现有什么不对this.OpenConnection（）。我的代码成功运行。你确定提供给connectionString的凭证是有效的吗？