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Old July 7th, 2005, 09:58 AM
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Default Converting a DataGrid.DataSource to a DataView

All:
I am trying to convert a DataGrid's DataSource to a DataView during the preRender event of the same DataGrid. My "catch" gets an InvalidCastException (Specified Cast is not valid). The ultimate point of the conversion is to get a count of the number of records in the DataGrid. My single line of code:

Me.labTest.Text =
CType(DG1.DataSource, DataView).count.ToString() + " records found"

Can anyone help me with this?

TIA,

Demivolt
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Old July 7th, 2005, 01:12 PM
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What is the datagrid's datasource?

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Old July 7th, 2005, 01:25 PM
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JBenson001:

The DataSource of my DataGrid is a DataSet drawn from a single
SQL Server 2000 Database. The SQL connection, query string and
adapter are located in function called from a VB module within my project.

Thanks,

Demivolt


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Old July 7th, 2005, 01:29 PM
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Me.labTest.Text = dataset.Tables(<table name or index>).Rows.Count

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Old July 7th, 2005, 02:58 PM
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Getting closer. I tried your suggested syntax --

 Me.labTest.Text = dataset.Tables(<table name or index>).Rows.Count

This returns ALL of the records in the table [tables(0)]. I am
wanting a count of only those records going to my DataGrid, i.e. the DataSource of my grid. The only records show up on my grid are based on a criterion triggered by selection from a dropdownList, which sets up a "where" clause in my SQL Select string.

I am thinking that I may be confused about what data is available during a preRender event. Can controls not be created and inserted on a form "on-the-fly" during this even????

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Old July 7th, 2005, 03:04 PM
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Does this help: http://Imar.Spaanjaars.Com/QuickDocId.aspx?QUICKDOC=356


Imar
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Old July 7th, 2005, 04:21 PM
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Imar:
I went to your URL. Your last paragraph was relevant to my case in that, unfortunately, I am using paging, and as stated, the count only returns a number equal to the PageSize.

Your last SENTENCE, however, sums up exactly what I need: " ... return the number of items in the original datasource that the control is bound to." Do you, or anyone, have a suggestion along these lines. Also, can the problem be my choice of the preRender Event?

Thank you,

Demivolt


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Old July 7th, 2005, 04:46 PM
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Either I am not understanding what you want, or you are missing a few concepts.

If you're not using paging, the DataGrid displays all records. Thus, the Items.Count returns all records currently displayed in the grid.

If you want to know all the records in the initial data source, ask the datasource ;)
Suppose you create a dataset with a query like this:

SELECT Col1, Col2 FROM YourTable WHERE SomeCriteria = SomeValue.

Let's say your *database* table holds 100 records, and that 20 are returned by this query. Let's also say your Grid has a PageSize of 10

Then this:

YourDataSet.Tables(0).Rows.Count

returns 20, as that is the number of records in a *DataTable* inside the DataSet, not the total number of records in the table in the *database*.

This:

MyDataGrid.Items.Count returns 10

and this:

SELECT COUNT(*) FROM YourTable


returns 100

So, now you can count whatever you want: items in the grid (Items.Count), items in the datasource (Tables(0).Rows.Count) or items in the database table (SELECT COUNT(*) FROM YourTable)

Is there anything more to count??

Imar
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Old July 8th, 2005, 09:33 AM
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Quote:
quote:Originally posted by demivolt
 I am thinking that I may be confused about what data is available during a preRender event.

I think the answer to the original question has been provided above, but I wanted to chime in with something.

The important thing to remember with a DataGrid is that the DataSource is only available during a page execution when the DataSource was set. It sounds like in your situation this is when you changed the selection of the DDL that establishes the criteria for the query. During a page execution where the DataSource has been set, you can interrogate this property, otherwise (postback not related to changing grid data) it will be null. Then you can't find out how many rows are in the grid's source data when paging is enabled. This is usually not a problem because you'd put the page count result into a label that is stateful and needn't be changed until you rebind the grid.

-Peter
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Old July 8th, 2005, 09:57 AM
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GOT IT!

Imar, your reply pushed me in a direction away from the preRender event and toward a closer inspection of how I was handling my DataSet.
I had a superfluous call to the database in the postback that was giving me unintended results--this was along the lines of what Planoie pointed out later.

Gentlemen, I truly appreciate your help. Have a pleasant weekend. I know I will, now.

Demivolt





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