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statements it is going to execute is not much better than dynamically generated SQL. What gets compiled and optimized is the code that generates the statement, not the actual execution of that statement. All the work that has to be done with dynamically generated SQL passed in as command text has to also be done with statements that are generated within a stored procedure and executed using sp_executesql or a similar facility built in to your database. This can become a problem when you re allowing your users to pick which columns they want to sort on. Either you need a stored procedure for each possible sort value or you need to dynamically generate the statement. Using a GridView, we ll show you some of the differences in solving this problem with a data reader and a DataSet. The GridView itself is very simple (see SortIE.aspx in Web10). <asp:GridView Runat=server ID=gvAuthors EnableViewState=false AllowSorting=True OnSorting="gvAuthors_Sorting" BorderWidth="1px" BackColor="White" GridLines="Vertical" CellPadding="3" BorderStyle="Solid" BorderColor="#999999" ForeColor="Black"> <FooterStyle BackColor="#CCCCCC" /> <PagerStyle ForeColor="Black" HorizontalAlign="Center" BackColor="#999999" /> <HeaderStyle ForeColor="White" Font-Bold="True" BackColor="Black" /> <AlternatingRowStyle BackColor="#CCCCCC" /> <SelectedRowStyle ForeColor="White" Font-Bold="True" BackColor="#000099" /> </asp:GridView> The grid is bound by a method named BindGrid. You ll be implementing several different versions of this method. This code will be common to all of the examples (see SortIE.aspx in Web10). protected void gvAuthors_Sorting(object sender, GridViewSortEventArgs e { BindGrid(e.SortExpression); } protected void Page_Load(object sender, EventArgs e) { BindGrid("au_id"); }
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The grid, when rendered, will be a simple dump of the author data (see Figure 10-2). The column headers, however, will be rendered as hyperlinks because you set AllowSorting to true in the declaration of the grid. Clicking on the column header is what causes the gvAuthors_Sorting event to fire on the server. The name of the column the user has clicked on will be passed along to this event trap as SortExpression.
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Figure 10-2. The authors data displayed in a grid for sorting First you ll dynamically generate the SQL (see SortIE.aspx in Web10). private void BindGrid(string sortExpr) { SqlConnection cn = new SqlConnection ConfigurationManager.ConnectionStrings ["localPubs"].ToString()); SqlCommand cm = new SqlCommand (string.Format( "select * from authors order by {0}", sortExpr), cn);
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cn.Open(); gvAuthors.DataSource = cm.ExecuteReader(); gvAuthors.DataBind(); cn.Close(); } When this page is put under load, it serves about 106 requests per second. Of course, this is specific to the machine that it s running on, but in the following examples, you ll be changing nothing except the data access method, so you should get a good relative gauge as to how these sorting methods compare. Next, you ll move the dynamic generation of the SQL into that database, using this stored procedure (script for this can be found in usp_SortAuthors.sql in the Code10 directory). create procedure usp_SortAuthors @sortExpr varchar(25) as declare @sql varchar(100) set @sql = 'select * from authors order by ' + @sortExpr EXEC(@sql) Go The BindGrid method of your test page will be modified to call this stored procedure instead of generating the SQL itself. The sort expression will be passed as a parameter to the stored procedure (see SortIE.aspx in Web10). private void BindGrid(string sortExpr) { SqlConnection cn = new SqlConnection ConfigurationManager.ConnectionStrings ["localPubs"].ToString()); SqlCommand cm = new SqlCommand("usp_SortAuthors", cn); cm.CommandType = CommandType.StoredProcedure; cm.Parameters.Add( new SqlParameter( "@sortExpr", SqlDbType.VarChar, 25)).Value = sortExpr; cn.Open(); gvAuthors.DataSource = cm.ExecuteReader(); gvAuthors.DataBind(); cn.Close(); }
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This method yields about 104 requests per second. Clearly, you re not getting the gains you d expect to by moving to a stored procedure. You re simply not saving the database any work; you re just moving the SQL generating logic into another process. Next you ll try a dedicated stored procedure for each column the user can sort by. You ll dynamically generate these stored procedures (see SortIE.aspx in Web10). private void GenSprocs() { SqlConnection cn = new SqlConnection ConfigurationManager.ConnectionStrings ["localPubs"].ToString()); SqlCommand cm = new SqlCommand("select * from authors", cn); DataSet ds = new DataSet(); cn.Open(); SqlDataAdapter da = new SqlDataAdapter(cm); da.Fill(ds); foreach (DataColumn dc in ds.Tables[0].Columns) { string sql = "create procedure usp_SortAuthors_{0} as " + "select * from authors order by {0}"; sql = string.Format(sql, dc.ColumnName); cm = new SqlCommand(sql, cn); cm.ExecuteNonQuery(); } cn.Close(); } Now you ll modify the BindGrid method to dynamically build the name of the stored procedure you ll call (see SortIE.aspx in Web10). private void BindGrid(string sortExpr) { SqlConnection cn = new SqlConnection(ConfigurationManager.ConnectionStrings ["localPubs"].ToString()); SqlCommand cm = new SqlCommand (string.Format("usp_SortAuthors_{0}",sortExpr), cn); cm.CommandType = CommandType.StoredProcedure;
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