数据库连接问题 [英] problem in database connectivity

问题描述

在运行此代码时，出现" executereader:连接属性尚未初始化"的运行时错误

I am getting run time error of "executereader:connection property has not been initialized", while running this code

 private void Form1_Load(object sender, EventArgs e)
        {

        }

        private void textBox1_TextChanged(object sender, EventArgs e)
        {

        }

        private void button1_Click(object sender, EventArgs e)
        {
             try
            {
                string sconnection;
                sconnection = "provider=microsoft.jet.oledb.4.0;" + "data source=intuitive.mdb";
                OleDbConnection dbconn;
                dbconn = new OleDbConnection(sconnection);
                dbconn.Open();


                OleDbCommand cmd = new OleDbCommand();
                OleDbDataReader dr = null;
                dr = cmd.ExecuteReader();
                 
                cmd.CommandText = "select * from table";

              //  dr = cmd.ExecuteReader();

                string userText = textBox1.Text;
                string passText = textBox2.Text;
             

                while (dr.Read())
                {
                   if (this.CompareStrings(dr["username"].ToString(), userText) &&
                        this.CompareStrings(dr["password"].ToString(), passText))
         
                    {
                        MessageBox.Show("OK");
                    }
                    else
                    {
                        MessageBox.Show("Error");
                    }

                }

                dr.Close();

                dbconn.Close();

            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }
    }
} 

请帮我解决这个问题.

Please help me out of this problem.

推荐答案

互换以下代码:

从:

Interchange the following codes:

FROM:

dr = cmd.ExecuteReader();
cmd.CommandText = "select * from table";

收件人:

TO:

cmd.CommandText = "select * from table";
dr = cmd.ExecuteReader();

问候，
Eduard

Regards,
Eduard

您的连接字符串有问题，请尝试以下操作.

There is problem in your connection string, try following.

Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\intuitive.mdb;User Id=UserID;Password=PWD;

您必须在执行任何查询之前初始化OleDbCommand对象的Connection属性.执行查询.

You have to initialize Connection Property of OleDbCommand object before executing any query.Write this code before executing your query.

cmd.Connection = dbconn

然后仍然会出现错误，请检查连接字符串.
请查看以下链接:连接字符串:)

and after that still there will be error then please check Connection String.
Check out following link :Connection Strings :)

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