使用 Visual Studio C# 从 MS Access 检索数据

本文关键字：Access 检索 数据 MS Visual Studio 使用 | 更新日期: 2023-09-27 18:31:24

好的，所以有点背景。我发现在 C# 中做一个共享 DLL 很困难，而且真的不值得麻烦，因为这只是一个几乎完成的学校项目，无论如何我宁愿走这条路。

所以我通过这段代码将数据放在MS Access中。

     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，这行得通。问题是当我尝试从数据库中检索数据时。

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

我无法将查询结果转换为双精度值。我不知道代码是错误的，还是我只是以错误的方式去做。提前谢谢。

使用 Visual Studio C# 从 MS Access 检索数据

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;
}

您需要创建/打开连接，然后执行查询。 您为插入做了此操作 - 现在您需要使用选择查询在 get 方法中创建相同的内容。 您需要执行查询，然后将查询结果转换为双精度值。

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