使用Visual Studio C從MS Access檢索數據＃

Question

好吧，有一點背景。我發現在C＃中使用共享DLL很困難，而且這真的不值得麻煩，因爲這僅僅是一個很好的學校項目，而且我寧願去這條路線。

因此，我通過這段代碼將數據存入MS Access。

 public void SetBal(double money) 
    { 
     bal = money; //balance equals whatever money that was sent to it 
     string query = "Insert into Users" + "([Money])" + "Values (@Money)" + "where Users.UserID = 1"; 
     dbconn = new OleDbConnection(connection); 
     OleDbCommand insert = new OleDbCommand(query, dbconn); 
     insert.Parameters.Add("Money", OleDbType.Char).Value = bal; 
     dbconn.Open(); 
     try 
     { 
      int count = insert.ExecuteNonQuery(); 
     } 
     catch (OleDbException ex) 
     { 

     } 
     finally 
     { 
      dbconn.Close(); 
     } 

    } 

好吧，那有效。問題是當我試圖從數據庫中檢索數據時。

public double GetBal() 
    { 
     string query = "SELECT Users.Money FROM Users"; 
     bal = Convert.ToDouble(query); 
     return bal; 
    } 

我無法將查詢結果轉換爲double。我不知道代碼是否錯誤，或者我只是以錯誤的方式去做。提前致謝。

Answer 1

您需要創建/打開您的連接，然後執行查詢。你爲插入做了 - 現在你需要使用select查詢在你的get方法中創建同樣的東西。您需要執行查詢，然後將查詢結果轉換爲double。

Answer 2

public double GetBal() 
{ 
    // Make sure you change this to a real userID that you pass in. 
    var query = "SELECT Users.Money FROM Users WHERE Users.UserID = 1"; 

    double balance = 0; 

    using (var dbconn = new OleDbConnection(connectionString)) { 
    var command = new OleDbCommand(query, dbconn); 
    dbconn.Open(); 

    // Send the command (query) to the connection, creating an 
    // OleDbReader in the process. We want it to close the database 
    // connection in the process so we pass in that behavior as an 
    // argument (CommandBehavior.CloseConnection) 
    var myReader = command.ExecuteReader(CommandBehavior.CloseConnection); 

    // this while loop will keep executing until there are no more rows 
    // to read from the database. myReader.Read() moves to the next row 
    // in the database too. The first read() puts you at the first row. 
    while(myReader.Read()) 
    { 
     // Use the reader's GetDouble() method to read the data and convert 
     // it to a double. The 0 is there because it is the first column in 
     // the results. for example to read the third column, it would be 
     // myReader.GetDouble(2). 
     balance = myReader.GetDouble(0)); 
    } 
    // because there is only one row (query said where Users.UserID = 1) the 
    // above loop will only execute once. 

    // Close the reader so we can tell the command that the connection 
    // can be closed...because CommandBehavior.CloseConnection was specified 
    myReader.Close(); 
    } 

    // return the value we got from the database 
    return balance; 
}