尝试将数据插入SQL Server数据库时打开连接问题

I have created a Main form with password request to login to next form depend on a username. Now here I have made another form with tabs. One tab for inserting data, other one for checking data.

我创建了一个带有密码请求的主表单，以便根据用户名登录到下一个表单。现在我在这里制作了另一个带标签的表格。一个用于插入数据的选项卡，另一个用于检查数据。

I have create the form like this Picture

我已经创建了像这张图片的表格

This is my code:

这是我的代码：

namespace Kartice
{
    public partial class Matjaz : Form
    {
    //   string KarticaMString = "Data Source=hostname;Initial Catalog=mydatabase;uid=uid;pwd=pwd;Integrated Security=True;";
      // SqlConnection KarticaM = new SqlConnection();
        public Matjaz()
        {
            InitializeComponent();
        }

    private void karticaMBindingNavigatorSaveItem_Click(object sender, EventArgs e)
    {
    }

    private void usersBindingNavigatorSaveItem_Click(object sender, EventArgs e)
    {
    }

    private void usersBindingNavigatorSaveItem_Click_1(object sender, EventArgs e)
    {
    }

    private void karticaMBindingNavigatorSaveItem_Click_1(object sender, EventArgs e)
    {
    }

    private void Matjaz_Load(object sender, EventArgs e)
    {
        // TODO: This line of code loads data into the 'kartice1.KarticaM' table. You can move, or remove it, as needed.
        this.karticaMTableAdapter.Fill(this.kartice1.KarticaM);

    }

    private void tabPage1_Click(object sender, EventArgs e)
    {

    }

    private void ExitBtn_Click(object sender, EventArgs e)
    {
        Application.Exit();

    }

    private void InsertBtn_Click(object sender, EventArgs e)
    {
        string Sqlquery = null;
       string  KarticaMString = null;

        using (SqlConnection conn = new SqlConnection(KarticaMString))
        {
            {
                Sqlquery = "INSERT INTO KarticaM (DateInsert, DateTransaction, Value, Purpose, DepositLift) VALUES (" + DateInsertPicker.Value + "," + DateTransactionPicker.Value + "," + ValueTxt.Text + "," + PurposeTxt.Text + "," + DepositLiftCombobox.SelectedText + ")";
                conn.Open();
                using (SqlCommand cmd = new SqlCommand(Sqlquery, conn))
                {
                    cmd.Parameters.Add("@DateInsert", SqlDbType.DateTime).Value = DateInsertPicker.Value;
                    cmd.Parameters.Add("@DateTransaction", SqlDbType.DateTime).Value = DateTransactionPicker.Value;
                    cmd.Parameters.Add("@Value", SqlDbType.Money).Value = ValueTxt.Text;
                    cmd.Parameters.Add("@Purpose", SqlDbType.Text).Value = PurposeTxt.Text;
                    cmd.Parameters.Add("DepositLift", SqlDbType.Text).Value = DepositLiftCombobox.SelectedValue;

                    cmd.ExecuteNonQuery();
                    cmd.Connection = conn;
                }
                conn.Close();
            }
        }

    }
  }
}

I got this error :( Error

我收到了这个错误:(错误

2 个解决方案

#1

Though your major or first Problem is ConnectionString is null, i could also find other errors from your code:

虽然你的主要或第一个问题是ConnectionString为null，我也可以从你的代码中找到其他错误：

1. Your ConnectionString is null .

1.您的ConnectionString为空。

 string  KarticaMString = null;//assign your connection string here    
 using (SqlConnection conn = new SqlConnection(KarticaMString))

Solution:

解：

assign the proper Connection String before assigning it to the SqlConnection object.

在将其分配给SqlConnection对象之前，请分配正确的连接字符串。

Example:

例：

string  KarticaMString = "Data Source=hostname;Initial   
Catalog=mydatabase;uid=uid;pwd=pwd;Integrated Security=True";

2. your Insert Into Statement can be attacked using SQL Injection.
Solution: Use Parametrised Queries.

2.使用SQL注入可以攻击您的Insert Into Statement。解决方案：使用参数化查询。

3. though you are assigning parameters using SqlCommand.Parameters.AddWithValue() they will not be reflected to your sql statement untill unless you specify those parameters in the sql statement.

3.虽然您使用SqlCommand.Parameters.AddWithValue（）分配参数，但除非您在sql语句中指定这些参数，否则它们不会反映到您的sql语句中。

Solution: first add the parameters in insert into statement then add the values to the respective parameters using SqlCommand.Parameters.AddWithValue() statement.

解决方案：首先在insert语句中添加参数，然后使用SqlCommand.Parameters.AddWithValue（）语句将值添加到相应的参数中。

4. you are assigning the SqlConnection object after calling the ExecuteNonQuery() Statement. Solution: Not Required as you have already done it before.

4.在调用ExecuteNonQuery（）语句后分配SqlConnection对象。解决方案：不需要，因为您之前已经完成了。

5. suggestion: what i feel is you dont need to close the SqlConnection object explicitly as you have declared it inside the using{} block, object Disposal willbe taken care by using block Solution: Remove the statement conn.Close();

5.建议：我觉得你不需要显式关闭SqlConnection对象，因为你已经在using {}块中声明它，对象Disposal将通过使用块解决方案解决方法：删除语句conn.Close（）;

Final Solution

最终解决方案

private void InsertBtn_Click(object sender, EventArgs e)
    {
       string Sqlquery = null;
       string  KarticaMString = "@Data Source=.\SQLEXPRESS;AttachDbFilename=C:\Users\Bojan\Desktop\Programiranje\School‌\Kartice\Kartice\Kartice.mdf;Integrated Security=True;User Instance=True";

        using (SqlConnection conn = new SqlConnection(KarticaMString))
        {

                Sqlquery = "INSERT INTO KarticaM (DateInsert, DateTransaction, Value, Purpose, DepositLift) VALUES (@DateInsert,@DateTransaction,@Value,@Purpose,@DepositLift)";
                conn.Open();
                using (SqlCommand cmd = new SqlCommand(Sqlquery, conn))
                {
                    cmd.Parameters.Add("@DateInsert", SqlDbType.DateTime).Value = DateInsertPicker.Value;
                    cmd.Parameters.Add("@DateTransaction", SqlDbType.DateTime).Value = DateTransactionPicker.Value;
                    cmd.Parameters.Add("@Value", SqlDbType.Money).Value = ValueTxt.Text;
                    cmd.Parameters.Add("@Purpose", SqlDbType.Text).Value = PurposeTxt.Text;
                    cmd.Parameters.Add("@DepositLift", SqlDbType.Text).Value = DepositLiftCombobox.SelectedValue;

                    cmd.ExecuteNonQuery();                    
                }


        }

    }

#2

Notice this:

注意这个：

string KarticaMString = null;

using (SqlConnection conn = new SqlConnection(KarticaMString))
{
    ...
}

The connection string, KarticaMString, is obviously null. You'll have to provide a valid connection string to the SqlConnection constructor. See ConnectionString for more information on how to write a valid connection string, or use a SqlConnectionStringBuilder.

连接字符串KarticaMString显然为null。您必须为SqlConnection构造函数提供有效的连接字符串。有关如何编写有效连接字符串或使用SqlConnectionStringBuilder的更多信息，请参阅ConnectionString。

#1