连接到MDB数据库C＃

Question

An unhandled exception of type 'System.Data.OleDb.OleDbException' occurred in System.Data.dll

Additional information: Could not use ''; file already in use This is where the error points at:

da.Fill(dt);

The database is located at C:\\ChattBankMDB.mdb on my computer.

Database: http://puu.sh/hjQj0/d86ede4c00.png

When I press the button1, I would like for the form to follow up and login on the Customer database else a messagebox.show will say failure to login.

Button on form:

public partial class CustLogin : Form {

OleDbConnection db = new OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\\ChattBankMDB.mdb");
OleDbDataAdapter da = new OleDbDataAdapter();
DataTable dt = new DataTable();
public CustLogin()
{
    InitializeComponent();
}

private void button1_Click(object sender, EventArgs e)
{
    da = new OleDbDataAdapter("Select CustID, CustPassword From Customers", db);
    da.Fill(dt);
    for (int i = 0; i < dt.Rows.Count; i++)
    {
        if (UserText.Text == dt.Rows[i]["CustID"] && PassText.Text == dt.Rows[i]["CustPassword"])
        {
            WelcomeCust f = new WelcomeCust();
            this.Hide();
            f.Show();
        }
        else
        {

            MessageBox.Show("FAILURE TRY AGAIN");
        }
    }
}

Answer 1

I've noticed a couple of potential issues:

• Database Injection.
• Password in plain text.
• Utilizing SqlConnection .

A .mdb isn't a SQL database, it is actually a Microsoft Access database. So you'll want to actually use ADO.NET connection. So your code should actually be:

private readonly string dbConnection = ConfigurationManager.ConnectionStrings["..."].ConnectionString;
private const string query = "SELECT * FROM [Example] WHERE ([Id] = @Id);";

public void Example()
{
     using(var connection = new OleDbConnection(dbConnection))
         using(var command = new OleDbCommand(query, connection))
         {
              // Apply parameter, open connection, etc.
         }
}

You utilize parameters to avoid a sub-query being introduced. As for your password in plain text you should take a look at BCrypt or another library for a Salt / Hash approach.

Then the change to the connection should alleviate your issue.

Your next issue I believe stems from the Fill being before you build your data table.

Answer 2

The database is an Acces database , so you need to use OleDB to connect to it.

Moreover, the query can cause errors.

Replace :

("Select* from Customers where CustID ='" + UserText.Text +"'
and CustPassword =" + PassText.Text + '"', conn)

By :

("Select * from Customers where CustID = '" + UserText.Text + "' 
and CustPassword = '" + PassText.Text + "'", conn);