c# - 错误 - 连接字符串属性尚未初始化(C# 数据库)？

Question

错误:

The error says:- The ConnectionString Property has not been initialized at system.data.OledbOledConnection.PermissionDemand().

我无法找出错误。谁能解释一下这是什么意思以及如何解决？

C#代码:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.OleDb;//microsoft database
namespace AccessLoginApp
{
public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();

    }

    private void Form1_Load(object sender, EventArgs e)
    {
        try
        {
            OleDbConnection connection = new OleDbConnection();
            connection.ConnectionString = @"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\Users\admin\Documents\Book Database.accdb;
        Persist Security Info=False;";

        }
        catch (Exception ex)
        {
            MessageBox.Show("Error"+ ex);
        }
    }

    private void button1_Click(object sender, EventArgs e)
    {

        try{
        OleDbConnection connection = new OleDbConnection();
        connection.Open();
        OleDbCommand command = new OleDbCommand();
        command.Connection = connection;
        command.CommandText = " Insert into Book Name(Book Name,Book Number,Publisher) values('" + bookName.Text + "','" + bookNumber.Text + "','" + publisher.Text + "')";
        command.ExecuteNonQuery();
        MessageBox.Show("Data Saved");


        }
        catch (Exception ex)
        {
            MessageBox.Show("Error" + ex);
        }

    }




}
}

Answer 1

表单加载中的变量connection和button1_Click事件是类OleDbConnection的不同实例(显然它们是不同的)和你尚未在 button1_Click 事件中使用连接字符串初始化连接变量(这也会导致错误)。如果你这样做意味着你的代码将运行良好，如果你将串联查询替换为参数化查询意味着你的代码将运行良好。而 using 语句的引入将使您的代码完美。您可以尝试以下操作:

string conString = @"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\Users\admin\Documents\Book Database.accdb;Persist Security Info=False;";
// This will be the connection string
private void Form1_Load(object sender, EventArgs e)
{
    // Need not to do anything regarding connection
    // some other statements if needed
}

private void button1_Click(object sender, EventArgs e)
{

    try
    {
        using (OleDbConnection connection = new OleDbConnection(conString)) // Create and initialize connection object
        {
            connection.Open();
            using (OleDbCommand command = new OleDbCommand())
            {
                command.Connection = connection;
                command.CommandText = " Insert into Book(Book_Name,Book_Number,Publisher) values(@BookName,@BookNumber,@Publisher)";
                command.Parameters.Add("@BookName", OleDbType.VarChar).Value = bookName.Text;
                command.Parameters.Add("@BookNumber", OleDbType.Integer).Value = bookNumber.Text;
                command.Parameters.Add("@Publisher", OleDbType.VarChar).Value = publisher.Text;                     
                command.ExecuteNonQuery();

            }
        }
      MessageBox.Show("Data Saved");
    }
    catch (Exception ex)
    {
        MessageBox.Show("Error" + ex);
    }

}