Question

几个月前，我为一个项目做了一个测试程序，一切都很好。现在我正在研究程序本身，所以我从测试程序中复制了代码更改了列，按钮等的名称，因此它适合当前程序。当我尝试在数据库中添加内容时，它在第一次单击时没有任何作用第二个弹出错误，表示连接已打开..我真的不知道是什么问题。我试图再次检查我是否在列名或数据库名称中出错但一切似乎都是正确的。注意：我还有一个显示数据库数据的函数，它没有任何问题。

private void InsertData()
{
    string NewCode = GenerateCode();
    string NewSentence = txtSentence.Text;
    string NewRow = NewRowNum();
    try
    {
        string AddData = "INSERT INTO ShopSentences (BinaryStrings,Sentence,RowNumber) VALUES (@NewBinaryString,@NewSentence,@NewRowNumber)";
        SqlCommand DataAdd = new SqlCommand(AddData, Connection);
        DataAdd.Parameters.AddWithValue("@NewBinaryString", NewCode);
        DataAdd.Parameters.AddWithValue("@NewNewSentence", NewSentence);
        DataAdd.Parameters.AddWithValue("@NewRowNumber", NewRow);
        Connection.Open();
        DataAdd.ExecuteNonQuery();
        Connection.Close();
    }
    catch (Exception e)
    {
        Console.WriteLine(e.ToString());
    }
}
//Checking the banary code in the last row
string GenerateCode()
{
    string RowNo = RowFind();
    int Row = int.Parse(RowNo);
    int Code = Row + 1;
    string Cd = Convert.ToString(Code, 2);
    int Ln = Cd.Trim().Length;
    if (Ln == 3)
    {
        Cd = "100" + Cd;
    }
    else if (Ln == 4)
    {
        Cd = "10" + Cd;
    }
    else if (Ln == 5)
    {
        Cd = "1" + Cd;
    }
    return Cd;
}
//Finding the last row
string RowFind()
{
    Connection.Open();
    string queryString = string.Format("SELECT * FROM ShopSentences");
    SqlDataAdapter sda = new SqlDataAdapter(queryString, Connection);
    DataTable dt = new DataTable("ShopSentences");
    sda.Fill(dt);
    Connection.Close();
    return dt.Rows[dt.Rows.Count - 1]["RowNumber"].ToString();
}
string NewRowNum()
{
    string Row = RowFind();
    int CalcRow = int.Parse(Row) + 1;
    Row = CalcRow.ToString();
    return Row;
}

看似打开的连接是字符串RowFind（）中的连接。

以下是数据库的其他相关内容：

public partial class frmShop : Form
{
    System.Data.SqlClient.SqlConnection Connection;

    public frmShop()
    {
        string DatabaseConnection = WindowsFormsApplication1.Properties.Settings.Default.BinaryStringsDictionaryConnectionString1;
        Connection = new System.Data.SqlClient.SqlConnection();
        Connection.ConnectionString = DatabaseConnection;
        InitializeComponent();
    }

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

    }

    private void GetSentence()
    {
        try
        {
            Connection.Open();
            SqlDataReader ReadSentence = null;
            Int32 BinaryInt = Int32.Parse(txtBinaryString.Text);
            string CommandString = "SELECT Sentence FROM ShopSentences WHERE BinaryStrings = @BinaryString";
            SqlCommand Command = new SqlCommand(CommandString, Connection);
            Command.Parameters.Add("@BinaryString", System.Data.SqlDbType.Int).Value = BinaryInt;
            ReadSentence = Command.ExecuteReader();
            while (ReadSentence.Read())
            {
                txtSentence.Text = (ReadSentence["Sentence"].ToString());
                Fit = 1;
            }
            Connection.Close();
        }
        catch (Exception e)
        {
            Console.WriteLine(e.ToString());
        }
    }
}

Answer 1

由于您多次重复使用相同的连接Connection.Open();，因此收到错误。

您的方法InsertData()使用相同的方法执行此操作3次。

您应该创建连接对象的新实例并将其置于您的方法上。

使用Statement是可行的方法。

private void InsertData()
{
    using (var Connection = new SqlConnection(DatabaseConnection))
    {
        string NewCode = GenerateCode();
        string NewSentence = txtSentence.Text;
        string NewRow = NewRowNum();
        try
        {
            Connection.Open();
            string AddData = "INSERT INTO ShopSentences (BinaryStrings,Sentence,RowNumber) VALUES (@NewBinaryString,@NewSentence,@NewRowNumber)";
            SqlCommand DataAdd = new SqlCommand(AddData, Connection);
            DataAdd.Parameters.AddWithValue("@NewBinaryString", NewCode);
            DataAdd.Parameters.AddWithValue("@NewNewSentence", NewSentence);
            DataAdd.Parameters.AddWithValue("@NewRowNumber", NewRow);
            DataAdd.ExecuteNonQuery();
            //Connection.Close(); no need to close
        }
        catch (Exception e)
        {
            Console.WriteLine(e.ToString());
        }
    }
}

如果存储RowFind()

返回的行，则可以再保存一个连接

string RowFind()
{
    using (var Connection = new SqlConnection(DatabaseConnection))
    {  
        Connection.Open();
        string queryString = string.Format("SELECT * FROM ShopSentences");
        SqlDataAdapter sda = new SqlDataAdapter(queryString, Connection);
        DataTable dt = new DataTable("ShopSentences");
        sda.Fill(dt);
        //Connection.Close();
        return dt.Rows[dt.Rows.Count - 1]["RowNumber"].ToString();
    }
}

所以你要连接一次而不是两次：

var Row  = RowFind();
string NewCode = GenerateCode(Row);
string NewRow = NewRowNum(Row);
string NewSentence = txtSentence.Text;

将属性的连接字符串变量声明为属性，以便重用它：

private string DatabaseConnection {get; set;}

Answer 2

相反，使用实例级别的SqlConnection，您应该只提供一个用于创建连接的公共工厂：

public partial class frmShop : Form
{
    private string ConnectionString
    {
        get { return WindowsFormsApplication1.Properties.Settings.Default.BinaryStringsDictionaryConnectionString1; }
    }

    public frmShop()
    {
        InitializeComponent();
    }

    private SqlConnection CreateConnection()
    {
        var conn = new SqlConnection(ConnectionString);
        conn.Open();
        return conn;
    }

    private void frmShop_Load(object sender, EventArgs e)
    {
        // TODO: This line of code loads data into the 'binaryStringsDictionaryDataSet.ShopSentences' table. You can move, or remove it, as needed.
        this.shopSentencesTableAdapter.Fill(this.binaryStringsDictionaryDataSet.ShopSentences);
    }
    private void GetSentence()
    {
        try
        {
            using (var conn = CreateConnection())
            {
                var BinaryInt = int.Parse(txtBinaryString.Text);
                var commandString = "SELECT Sentence FROM ShopSentences WHERE BinaryStrings = @BinaryString";
                using (var Command = new SqlCommand(commandString, conn))
                {
                    Command.Parameters.Add("@BinaryString", System.Data.SqlDbType.Int).Value = BinaryInt;

                    using (var readSentence = Command.ExecuteReader())
                    {
                        while (readSentence.Read())
                        {
                            txtSentence.Text = (readSentence["Sentence"].ToString());
                            Fit = 1;
                        }
                    }
                }
            }
         }

        catch (Exception e)
        {
            Console.WriteLine(e.ToString());
        }
    }

    private void InsertData()
    {
        try
        {
            using (var conn = CreateConnection())
            {
                var commandString = "INSERT INTO ShopSentences (BinaryStrings,Sentence,RowNumber) VALUES (@NewBinaryString,@NewSentence,@NewRowNumber)";
                using (var comm = new SqlCommand(commandString, conn))
                {
                    comm.Parameters.AddWithValue("@NewBinaryString", GenerateCode());
                    comm.Parameters.AddWithValue("@NewNewSentence", txtSentence.Text);
                    comm.Parameters.AddWithValue("@NewRowNumber", NewRowNum());

                    comm.ExecuteNonQuery();
                }
            }
        }
        catch (Exception e)
        {
            Console.WriteLine(e.ToString());
        }
    }
    //Checking the banary code in the last row
    string GenerateCode()
    {
        string RowNo = RowFind();
        int Row = int.Parse(RowNo);
        int Code = Row + 1;
        string Cd = Convert.ToString(Code, 2);
        int Ln = Cd.Trim().Length;
        if (Ln == 3)
        {
            Cd = "100" + Cd;
        }
        else if (Ln == 4)
        {
            Cd = "10" + Cd;
        }
        else if (Ln == 5)
        {
            Cd = "1" + Cd;
        }
        return Cd;
    }
    //Finding the last row
    string RowFind()
    {
        using (var conn = CreateConnection())
        {
            var commandString = "SELECT * FROM ShopSentences";
            using (var comm = new SqlCommand(commandString, conn))
            {
                using (var sda = new SqlDataAdapter(queryString, Connection))
                {
                    using (DataTable dt = new DataTable("ShopSentences"))
                    {
                        sda.Fill(dt);
                        return dt.Rows[dt.Rows.Count - 1]["RowNumber"].ToString();
                    }
                }
            }
        }
    }

    string NewRowNum()
    {
        var Row = RowFind();
        var CalcRow = int.Parse(Row) + 1;
        return CalcRow.ToString();


}
}

但这只是一个开始，你不应该在你的Form类中有任何硬SQL依赖。

Answer 3

在代码中多次共享同一个SqlConnection实例时，不是直接打开，而是先检查连接状态，然后再打开它（如果尚未打开）。例如：

if(Connection.State!= ConnectionState.Open)
       Connection.Open();

连接已打开

3 个答案: