「ExecuteNonQuery：連接屬性尚未初始化。」

Question

下面是代碼：

string str = ("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:/Users/charlyn_dale/Documents/Visual Studio 2010/Projects/LMS/WindowsFormsApplication2/Accounts.accdb;Persist Security Info=False"); 
      OleDbCommand conn = new OleDbCommand(str); 
      con.Open(); 
      string query = "insert into Account ([Username],[Password],FirstName,MiddleName,LastName,Age,Section,Gender,Address,AccountStatus) values('" + txt1.Text + "','" + txt2.Text + "','" + txt4.Text + "','" + txt5.Text + "','" + txt6.Text + "','" + txt7.Text + "','" + txt8.Text + "','" + cmb2.Text + "','" + txt9.Text + "','" + cmb1.Text + "')"; 
      OleDbCommand cmd = new OleDbCommand(query, con); 
      conn.ExecuteNonQuery(); 
      MessageBox.Show("Registration Success!"); 
      con.Close(); 

和錯誤是：

連接屬性尚未初始化

Answer 1

有你的Access數據庫3個主要問題連接：

1. OleDbConnection連接字符串屬性在打開OLE DB連接時未初始化（請注意，con與此上下文中的conn不同）。

2. 錯誤地分配給變量conn的連接字符串聲明爲OleDbCommand，請改爲使用OleDbConnection。

3. 連接字符串數據源路徑似乎通過使用斜線符號爲目錄分隔符（假定目標文件存在Windows文件夾中），可使用反斜槓轉義序列（\\）或用文字串單反斜線代替（例如@"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\Users\......"）無效。

因此，正確的連接順序應該是這樣的：

string str = ("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\\Users\\charlyn_dale\\Documents\\Visual Studio 2010\\Projects\\LMS\\WindowsFormsApplication2\\Accounts.accdb;Persist Security Info=False"); 

using (OleDbConnection conn = new OleDbConnection(str)) 
{ 
    conn.Open(); 

    // security tips: better use parameter names to prevent SQL injection on queries 
    // and put value checking method for all textbox values (sanitize input) 
    string query = "insert into Account ([Username],[Password],FirstName,MiddleName,LastName,Age,Section,Gender,Address,AccountStatus) values ('" + txt1.Text + "','" + txt2.Text + "','" + txt4.Text + "','" + txt5.Text + "','" + txt6.Text + "','" + txt7.Text + "','" + txt8.Text + "','" + cmb2.Text + "','" + txt9.Text + "','" + cmb1.Text + "')"; 
    using (OleDbCommand cmd = new OleDbCommand(query, conn)) 
    { 
     conn.ExecuteNonQuery(); 
    } 
    ... // other stuff 
    conn.Close(); 
} 

注：由於添加到OLE DB連接using報表應立即使用，以騰出資源後丟棄。

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