Re: Handling data relations in Gridview

Hi

Thanks for a very thorough response. You have hit the proverbial nail
on the head, understanding my "problem" exactly. Your experience on
the newsgroups is finally paying dividends I see (ha ha).

Anyway, though I understand your answer and your proposed workaround, I
can't say that I like it. I guess the alternative to achieving the
same functionality is to use stored procedures for the CRUD interface
but ... you lose the caching from the dataset, Correct? So if I had a
child row of 1000 items that each had a relation or two that mapped a
FK into a readable tag (city name vs an index), would I have to go back
to the DB through a tableadapter query "select city_name from citylist
(where index = @index)" or would I have the name of the city as part of
the join 1000 times (if the child records all came from the same city)?
There is something slightly annoying about both of these.

Are there any other options? The one I outlined below is interesting,
but it seems you are getting the same data twice. If I could some how
Fill()'s for the two related tables (two fills thru two table
adapters), then build a third table from the cached tables to satisfy
the relation .... Am I insane or is there something missing from the
FW?

A custom BL would still have to pass back a joined table by "doing" the
relation in the Get method. Is this a bad thing too?

Thanks again

Bill

Steven Cheng[MSFT] wrote:
Hello Bill,

Welcome to the ASPNET newsgroup.

From your description, you're building a data display page in ASP.NET
application(2.0). Currently you have
a Dataset that contains multiple datatables which have relationship with
eachother, however, when bind a certain datatable in the dataset to a
Gridview, you found the gridview only display one dimension data only (with
out the related parent table's values) and you're wondering how to make the
GridView display the related table's data(through the foreign key column),
correct? If there is anything I missed or didn't quite address, please feel
free to let me know.

Based on my understanding, the behavior yet is expected due to the ASP.NET
webform page's databinding mechanism. ASP.NET template control databinding
is quite different from winform control databinding. In winform, since the
datasoure is always in memory, the databound context is easy to track the
datasource and navigate between the current bound datatable to its related
parent or child table. However, in ASP.NET since the page must be flushed
and write out to clent, it can not hold the datasource in memory forever,
it just query the current attached datasource(table or view) and bind that
direct attached table/view's data/columns to the databound
control(Gridview, datagrid ....). that's why you'll find GridView directly
display the foreign key value rather than the detailed value in
parent/child table/view.

To resolve this in webform page, we need to manually customize the
databinding process. for example, we can use the databound control such as
GridView's Item/Row DataBound event to do the customization.


#GridView.RowDataBound Event
http://msdn2.microsoft.com/en-us/library/system.web.ui.webcontrols.gridview.
rowdatabound.aspx

In the RowDataBound event, we can access the current GridView Row's inner
sub controls(in each gridviewRow column). Also, we can access the current
databound data item(such as DataRowview). Then, we can manualy get the
related data (parent or sub rows through the DAtaRowView) and use it to
modify the certain Gridview row column's controls. for example:


the following Gridview is bound to a DataView(from a datatable which
contains the Northwind "products" table's data), and the container dataset
also contains another datatable ("categories" table in northwind), I add a
relation between them and bind the products view to the GridView. In the
RowDataBound event, I manually query parent row data from Categories table:


=====aspx template==========

<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False"
OnRowDataBound="GridView1_RowDataBound">
<Columns>
<asp:BoundField DataField="ProductID"
HeaderText="ProductID" />
<asp:BoundField DataField="ProductName"
HeaderText="ProductName" />
<asp:TemplateField HeaderText="Category">
<EditItemTemplate>
<asp:TextBox ID="txtCategory" runat="server"
Text='<%# Bind("CategoryID") %>'></asp:TextBox>
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="lblCategory" runat="server"
Text='<%# Bind("CategoryID") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
</Columns>
</asp:GridView>

==============code behind==============

protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
PerformDataBind();
}
}

protected void PerformDataBind()
{
//get the dataset which contains two datatables that have relation
DataSet ds = GetDataSet();

ds.Relations.Add("products_categories",
ds.Tables[1].Columns["CategoryID"], ds.Tables[0].Columns["CategoryID"]);


GridView1.DataSource = ds.Tables[0].DefaultView;

GridView1.DataBind();
}


protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
{
if (e.Row.RowType == DataControlRowType.DataRow)
{
DataRowView product = e.Row.DataItem as DataRowView;

string strCategory =
product.Row.GetParentRow("products_categories")["CategoryName"] as string;

Label lbl = e.Row.FindControl("lblCategory") as Label;

lbl.Text = strCategory;
}
}

=========================

Hope this helps. If you have anything unclear on this, please feel free to
post here.

Regards,

Steven Cheng
Microsoft Online Community Support


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