如何在会话中保存SQL查询以供以后使用

Question

I have a function which runs a query each time a button is pressed or each time any of the 7 DropDownList selection has been changed. How can I change the existing method to use Session or ViewState so my page will run the query once and then query against the Session or ViewState instead of going out to my SQL server for every request?

Code-Behind:

protected void Page_Load(object sender, EventArgs e)
{
    strMainQuery = @"SELECT  'http://dddfgdgdfg?objectid=' + CT.OBJECTID + '&classid=1224' 'Task Detail'
            ,LTRIM(RTRIM(CT.ATTR2846)) 'Service'
            ,LTRIM(RTRIM(CT.ATTR2812)) 'Status'
            ,CONVERT(VARCHAR(14), CT.ATTR2752, 110) 'Due Date'
            ,LTRIM(RTRIM(CT.ATTR2739)) 'Task Name'
            ,LTRIM(RTRIM(UA.REALNAME)) 'Owner'
            ,LTRIM(RTRIM(CT.ATTR2799)) 'Client'

        FROM HSI.RMOBJECTINSTANCE1224 CT INNER JOIN HSI.RMOBJECTINSTANCE1232 S ON CT.ATTR2846 = S.ATTR2821 INNER JOIN HSI.USERACCOUNT UA ON S.FK2852 = (UA.USERNUM * -1)";


    if (!Page.IsPostBack)
    {
        ViewState["sortOrder"] = "Asc";
        ViewState["sortExp"] = "Due Date";
        PullData("Due Date", "Asc"); //ASC: A (top) to Z (bottom) || # (low to high) || Date (oldest to newest)
    }
    else
    {
        PullData(ViewState["sortExp"].ToString(), ViewState["sortOrder"].ToString());
    }
}

public void PullData(string sortExp, string sortDir)
{
    string query = "";
    DataTable taskData = new DataTable();
    connString = ""; //connection string
    if (ddlTaskName.SelectedIndex > 0)
    {
        strClause += " AND CT.ATTR2739 = '" + ddlTaskName.SelectedItem.Text + "'";
    }
    else
    {
        strClause += " AND CT.ATTR2739 LIKE '%'";
    }
    if (ddlService.SelectedIndex > 0)
    {
        strClause += " AND CT.ATTR2846 = '" + ddlService.SelectedItem.Text + "'";
    }
    else
    {
        strClause += " AND CT.ATTR2846 LIKE '%'";
    }
    if (ddlStatus.SelectedIndex > 0)
    {
        strClause += " AND CT.ATTR2812 = '" + ddlStatus.SelectedItem.Text + "'";
    }
    else
    {
        strClause += " AND CT.ATTR2812 LIKE '%'";
    }
    if (ddlDueDate.SelectedIndex > 0)
    {
        strClause += " AND CONVERT(VARCHAR(14), CT.ATTR2752, 110) = '" + ddlDueDate.SelectedItem.Text + "'";
    }
    else
    {
        strClause += " AND CONVERT(VARCHAR(14), CT.ATTR2752, 110) LIKE '%'";
    }
    if (ddlOwner.SelectedIndex > 0)
    {
        strClause += " AND UA.REALNAME = '" + ddlOwner.SelectedItem.Text + "'";
    }
    else
    {
        strClause += " AND UA.REALNAME LIKE '%'";
    }
    if (ddlClient.SelectedIndex > 0)
    {
        strClause += " AND CT.ATTR2799 = '" + ddlClient.SelectedItem.Text + "'";
    }
    else
    {
        strClause += " AND CT.ATTR2799 LIKE '%'";
    }

    if (ddlTaskName.SelectedIndex == 0 && ddlService.SelectedIndex == 0 && ddlStatus.SelectedIndex == 0 && ddlDueDate.SelectedIndex == 0 && ddlOwner.SelectedIndex == 0 && ddlClient.SelectedIndex == 0)
    {
        query = strMainQuery + " WHERE CT.ACTIVESTATUS = 0";
    }
    else
    {
        query = strMainQuery + " WHERE CT.ACTIVESTATUS = 0" + strClause;
    }

    using (SqlConnection conn = new SqlConnection(connString))
    {
        try
        {
            SqlCommand cmd = new SqlCommand(query, conn);

            // create data adapter
            SqlDataAdapter da = new SqlDataAdapter(query, conn);
            // this will query your database and return the result to your datatable

            DataSet myDataSet = new DataSet();
            da.Fill(myDataSet);

            DataView myDataView = new DataView();
            myDataView = myDataSet.Tables[0].DefaultView;

            if (sortExp != string.Empty)
            {
                //MessageBox.Show(sortExp);
                //MessageBox.Show(sortDir);
                myDataView.Sort = string.Format("{0} {1}", sortExp, sortDir);
            }

            yourTasksGV.DataSource = myDataView;
            yourTasksGV.DataBind();

            TasksUpdatePanel.Update();

            conn.Close();
        }
        catch (Exception ex)
        {
            string error = ex.Message;
        }
    }
}

As you can see, each time PullData is called, it is going out to the SQL server and running the query which will eventually slow down once I start to have more and more data.

How can I convert the existing method to query once and save to a Session/ViewState so I don't have to query against SQL server each time?

Answer 1

Before running the query, check the cache. If its there, use it. If not, run the query and add the resulting data into Cache.

You could use Cache.Insert Method (String, Object, CacheDependency, DateTime, TimeSpan) . You can find some great caching tips: ASP.NET Caching: Techniques and Best Practices .

Here is how I would structure the PullData method:

public void PullData(string sortExp, string sortDir)
{
    // build your query string
    // ...

    // Now create a hash of that query string
    string cacheKey = HashHelper(query);

    DataSet ds = null;

    // check cache if key exists
    if(Cache[cacheKey] != null)
    {
         // read dataset from cache
         ds = (DataSet)Cache[cacheKey];
    }
    else
    {
        // perform sql command and fill your dataset
        // ....
        // save dataset to cache for 30 minutes or whatever you like
        Cache.Insert(cacheKey, ds, null, DateTime.Now.AddMinutes(30), TimeSpan.Zero);
    }

    // Get DataView based on sort options
    DataView myDataView = new DataView();
    myDataView = ds.Tables[0].DefaultView;

    if (sortExp != string.Empty)
    {
        myDataView.Sort = string.Format("{0} {1}", sortExp, sortDir);
    }

    yourTasksGV.DataSource = myDataView;
    yourTasksGV.DataBind();

    TasksUpdatePanel.Update();

    // keep calm and carry on
}

Here is my Hash Helper

private string HashHelper(string query)
{
    using (SHA256Managed hashEngine = new SHA256Managed())
    {
        byte[] data = hashEngine.ComputeHash(Encoding.UTF8.GetBytes(query));
        StringBuilder hash = new StringBuilder(64);
        for (int i = 0; i < data.Length; i++)
        {
            hash.Append(data[i].ToString("x2"));
        }
        return hash.ToString();
    }

}

Answer 2

With your current structure of code you can not do it. Because your strMainQuery has the sql statement without the WHERE clause and as the dropdown value changes you are dynamically building the conditions for the WHERE clause. So you can't store that result set in session as the values change with every dropdown selection.

Here is what you can do.

1. Retrieve all records for strMainQuery without any WHERE condition and store the results in session or some other state management. So your PullData method will contain

    SqlCommand cmd = new SqlCommand(strMainQuery, conn); 

2. As the dropdown value changes access the session object and use LINQ to filter the data based on the values for different dropdown. This will at least help you not to access the database server for every dropdown value changes, rather

   Fetch once => store it => and do additional data filtering using LINQ

   Before you bind the grid in the below lines do the data filtering.

    // do the data filtering against the data source based on dropdown selected values yourTasksGV.DataSource = myDataView; yourTasksGV.DataBind(); 

I do see that you are calling PullData in both !Page.IsPostBack as well as in the else part the PageLoad which means that this function PullData will be called every time there is a postback triggered by any other controls on the page. Rather add a OnSelectedIndexChanged event for the dropdowns and call the PullData method.