sqlCommandBuilder更新未按预期工作

Question

我正在尝试使用CommandBuilder进行更新。当通过按钮命令检索获取数据的代码时，代码工作得很好，但是当我从page_load获取数据时，更新失败。

该程序只需从数据库中获取数据，然后使用sqlCommandBuilder对特定表进行更新。

我搞不懂到底是怎么回事。

下面是失败的代码。

  private Users users;

protected void Page_Load(object sender, EventArgs e)
{
    users = (Users)Session["Users"];

    string connectionString = ConfigurationManager.ConnectionStrings["DBCS"].ConnectionString;
    SqlConnection connection = new SqlConnection(connectionString);
    string selectQuery = "Select * from Candidate where Candidate_ID = " + users.Candidate_ID;
    SqlDataAdapter dataAdapter = new SqlDataAdapter(selectQuery, connection);

    DataSet dataSet = new DataSet();
    dataAdapter.Fill(dataSet, "Candidates");
    ViewState["DATASET"] = dataSet;
    ViewState["SELECT_QUERY"] = selectQuery;

    if (dataSet.Tables["Candidates"].Rows.Count > 0)
    {
        DataRow dataRow = dataSet.Tables["Candidates"].Rows[0];


        txtLastName.Text = dataRow["LastName"].ToString();
        txtCity.Text = dataRow["City"].ToString();
        ddlGender.SelectedValue = dataRow["Gender"].ToString();
        lblStatus.Text = "";
    }
    else
    {
        lblStatus.ForeColor = System.Drawing.Color.Red;
        lblStatus.Text = "No record with ID = " + txtCandidateID.Text;
    }


}


protected void btnUpdate_Click(object sender, EventArgs e)
{
    string connectionString = ConfigurationManager.ConnectionStrings["DBCS"].ConnectionString;
    SqlConnection con = new SqlConnection(connectionString);

    SqlDataAdapter dataAdapter = new SqlDataAdapter();
    dataAdapter.SelectCommand = new SqlCommand((string)ViewState["SELECT_QUERY"], con);
    SqlCommandBuilder builder = new SqlCommandBuilder(dataAdapter);

    DataSet ds = (DataSet)ViewState["DATASET"];

    DataRow dr = ds.Tables["Candidates"].Rows[0];

    dr["LastName"] = txtLastName.Text;
    dr["Gender"] = ddlGender.SelectedValue;
    dr["City"] = txtCity.Text;

    int rowsUpdated = dataAdapter.Update(ds, "Candidates");
    if (rowsUpdated == 0)
    {
        lblStatus.ForeColor = System.Drawing.Color.Red;
        lblStatus.Text = "No rows updated";
    }
    else
    {
        lblStatus.ForeColor = System.Drawing.Color.Green;
        lblStatus.Text = rowsUpdated.ToString() + " row(s) updated";
    }
}

以下是完美工作的代码。

 protected void Page_Load(object sender, EventArgs e)
{


}


protected void btnUpdate_Click(object sender, EventArgs e)
{
    string connectionString = ConfigurationManager.ConnectionStrings["DBCS"].ConnectionString;
    SqlConnection con = new SqlConnection(connectionString);

    SqlDataAdapter dataAdapter = new SqlDataAdapter();
    dataAdapter.SelectCommand = new SqlCommand((string)ViewState["SELECT_QUERY"], con);
    SqlCommandBuilder builder = new SqlCommandBuilder(dataAdapter);

    DataSet ds = (DataSet)ViewState["DATASET"];

    DataRow dr = ds.Tables["Candidates"].Rows[0];

    dr["LastName"] = txtLastName.Text;
    dr["Gender"] = ddlGender.SelectedValue;
    dr["City"] = txtCity.Text;

    int rowsUpdated = dataAdapter.Update(ds, "Candidates");
    if (rowsUpdated == 0)
    {
        lblStatus.ForeColor = System.Drawing.Color.Red;
        lblStatus.Text = "No rows updated";
    }
    else
    {
        lblStatus.ForeColor = System.Drawing.Color.Green;
        lblStatus.Text = rowsUpdated.ToString() + " row(s) updated";
    }
}




protected void btnFetchData_Click(object sender, EventArgs e)
{
    users = (Users)Session["Users"];

    string connectionString = ConfigurationManager.ConnectionStrings["DBCS"].ConnectionString;
    SqlConnection connection = new SqlConnection(connectionString);
    string selectQuery = "Select * from Candidate where Candidate_ID = " + users.Candidate_ID;
    SqlDataAdapter dataAdapter = new SqlDataAdapter(selectQuery, connection);

    DataSet dataSet = new DataSet();
    dataAdapter.Fill(dataSet, "Candidates");
    ViewState["DATASET"] = dataSet;
    ViewState["SELECT_QUERY"] = selectQuery;

    if (dataSet.Tables["Candidates"].Rows.Count > 0)
    {
        DataRow dataRow = dataSet.Tables["Candidates"].Rows[0];


        txtLastName.Text = dataRow["LastName"].ToString();
        txtCity.Text = dataRow["City"].ToString();
        ddlGender.SelectedValue = dataRow["Gender"].ToString();
        lblStatus.Text = "";
    }
    else
    {
        lblStatus.ForeColor = System.Drawing.Color.Red;
        lblStatus.Text = "No record with ID = " + txtCandidateID.Text;
    }
}

Answer 1

你错过了Page.IsPostBack的支票吗？

请记住，在ASP.NET中，单击服务器按钮时，在单击事件按钮中的代码之前调用Page_Load中的代码。

不带

protected void Page_Load(object sender, EventArgs e)
{ 
     if(!Page.IsPostBack)
     {
         // load data
     }

}

重新加载数据集的代码将再次执行，当您在按钮单击事件中接收到控件时，您的更改将丢失。

Answer 2

fisrt对您的源代码进行调试。

在每一行上创建断点，并检查哪些值存储在变量包中。

还可以在try catch块中调试purpouse。

当您了解错误发生的位置时，您可以检查以修复问题。

您收到哪种类型的错误？？

另一个假设用户总是处于session.Take状态的东西是aspnet使用自定义方法循环会话，并且您可以使会话为空，因为iis应用程序池已重新启动。

是在进行强制转换之前检查会话(值)是否为空的良好实践。