Question

在下面的代码中，我只想根据更改的选定组合框填充我的文本框。但我得到以下错误。

转换varchar值时转换失败 'System.Data.DataRowViewConvert.ToString（）'到数据类型int。'

如果你帮助我，我会很感激。

SqlConnection objConnection = new SqlConnection(@"Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=C:\UniversityDataBase.mdf;Integrated Security=True");
        private void comboBox1_Click(object sender, EventArgs e)
        {
            string query = "SELECT *FROM TutorTable";
            SqlDataAdapter SDA = new SqlDataAdapter(query, objConnection);
            DataTable dt = new DataTable();
            SDA.Fill(dt);
            comboBox1.DataSource = dt;
            comboBox1.DisplayMember = "Tid";
            objConnection.Close();
        }

    private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
    {
        string sqlQuery = "SELECT *FROM TutorTable where Tid = '"+comboBox1.Text+ "Convert.ToString()'";
        SqlCommand objCommand = new SqlCommand(sqlQuery, objConnection);
        objConnection.Open();
        objCommand.ExecuteNonQuery();
        SqlDataReader dr;
        dr = objCommand.ExecuteReader();
        while (dr.Read())
        {
            string Tname = (string)dr["Tname"].ToString();
            textBox1.Text = Tname;
        }

    }

Answer 1

为什么在这段代码中使用Convert.ToString（）：

"SELECT * FROM TutorTable where Tid = '"+comboBox1.Text+ "Convert.ToString()'"

我认为正确的方法是：

"SELECT * FROM TutorTable where Tid = '"+comboBox1.Text+ "'"

但是考虑使用存储过程来阻止sql注入或使用ORM。

我认为comboBox1.Text已经返回一个字符串值。所以，如果是这样，就没有必要放Convert.ToString(comboBox.Text)，只需要把comboBox1.Text

根据文档，Text属性是一个字符串 https://msdn.microsoft.com/en-us/library/system.windows.forms.combobox.text(v=vs.110).aspx

Answer 2

我发现解决方案如下：

private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
    {
        SqlConnection con = new SqlConnection(@"Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=C:\UniversityDataBase.mdf;Integrated Security=True");
        string sqlQuery = "SELECT *FROM TutorTable WHERE Tid = '" + comboBox1.Text + "'";
        SqlCommand objCommand = new SqlCommand(sqlQuery, con);
        con.Open();
        SqlDataReader dr;
        dr = objCommand.ExecuteReader();
        while (dr.Read())
        {
            string name = (string)dr["Tname"].ToString();
            textBox1.Text = name;
        }
    }

Answer 3

你已经得到了答案，但还有更多事情需要处理

您的代码

private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
{
    string sqlQuery = "SELECT *FROM TutorTable where Tid = '"+comboBox1.Text+ "Convert.ToString()'";
    SqlCommand objCommand = new SqlCommand(sqlQuery, objConnection);
    objConnection.Open();
    objCommand.ExecuteNonQuery();
    SqlDataReader dr;
    dr = objCommand.ExecuteReader();
    while (dr.Read())
    {
        string Tname = (string)dr["Tname"].ToString();
        textBox1.Text = Tname;
    }

}

需要注意的事项：

1）使用varabled而不是操纵sql 例如SELECT *FROM TutorTable where Tid = @id并将id传递给sqlCommand对象

2）您无需在ExecuteNonQuery

之前致电SqlDataReader

3）您需要使用if(dr.Read()）而不是while

4）您可以直接指定值文本框。例如texBox1.Text = dr["Tname"].ToString();

5）关闭objConnection

填充文本框，当组合框选择索引更改时

3 个答案: