Read()를 호출하기 전에 필드에 액세스 할 수 없습니다.

Question

오류가 발생했습니다 : Read() 을 호출하기 전에 필드에 액세스하려는 시도가 잘못되었습니다. string result = Reader.GetString (0);

내가 할 것을 완전히 확실하지 않다 또는 무슨 잘못

internal int GetCharGuidByName(string charactername, MySqlConnection connection) 
{ 
    MySqlCommand command = connection.CreateCommand(); 
    MySqlDataReader Reader; 
    command.CommandText = "SELECT guid FROM characters WHERE name=\""+charactername+"\";"; 
    // Initialize MySQL Reader 
    Reader = command.ExecuteReader(); 
    Reader.Read(); 
    string result = Reader.GetString(0); 
    // If the character doesn't exist or isn't entered, return 0 
    int charguid = 0; 
    if (result != String.Empty) 
    { 
     charguid = Convert.ToInt32(result); 
    } 
    return charguid; 
} 

Answer 1

변경 비록 코드 :

이

Reader = command.ExecuteReader(); 
int charguid = 0; 
if(Reader.Read()) 
{ 
    if(Reader[0] != DBNull.Value) 
    { 
     if(int.TryParse(Reader[0].ToString(), out charguid)) 
     { 
     //value read and is an integer! 
     } 
    } 
} 
return charguid; 

Answer 2

대신

ExecuteSaclar returns the first column of the first row in the result set, or a null reference

ExecuteReader will return as resultset which you have to then iterate to read

가 ExecuteReader

의 ExecuteScalar는을 사용한다 따라서 코드를 살펴보면 결과 집합의 첫 번째 열만 입력하면됩니다.

internal int GetCharGuidByName(string charactername, MySqlConnection connection) 
{ 
    int charguid = 0; 

    using(MySqlCommand command = connection.CreateCommand()) 
    { 
     command.CommandText = "SELECT guid FROM characters WHERE name=\""+charactername+"\";"; 
     object obj = command.ExecuteScalar(); 
     if (obj != null && obj != DBNull.Value) 
     { 
     charguid = Convert.ToInt32(obj); 
     } 
    } 

     return charguid; 
} 

Answer 3

  openConnection() 

      sql = "SELECT last, first, emp_type, active FROM employee INNER JOIN account ON employee.emp_id = account.emp_id WHERE employee.emp_id = '" & AtxtEmpID.Text & "'" 

      command = New MySqlCommand(sql, mySqlConnection) 

      reader = command.ExecuteReader 

      reader.Read() 

      AtxtEmpName.Text = reader.Item(0) & ", " & reader.Item(1) 

      closeConn() 

은이 문제에 저장이