Adding Table to Dataset

Colonel Angus · September 27th, 2004, 08:40 AM

I am getting an error trying to add a new table to my dataset, "Object reference not set to an instance of an object". (Usually this means I left out a "New" keyword somewhere.)

Here's what I've got:

Code:

dim ds as New Dataset
Dim myTable As New DataTable
Dim newRow As DataRow

newRow.Item("myItem") = somevalue
myTable.Rows.Add(newRow)
dsResult.Tables.Add("myTable")
Return dsResult

It compiles ok, but I get that error at runtime. I think I am missing a step in here with adding in the Item, but I'm not sure.

Thanks in advance for your comments.

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In God we trust, everything else we test.

planoie · September 27th, 2004, 09:20 AM

Like you said, you left out a "new"

Dim newRow As new DataRow

newRow.Item("myItem") = somevalue

However, I think you'll have further problems. You can't just create a new row. You'll need to add columns to the new DataTable, then you create the new row from the table so the row knows what columns are in it. Then you can set values of the row.

Colonel Angus · September 27th, 2004, 09:31 AM

Actually,

Code:

Dim newRow As new DataRow

gives it's own error. This was something I was pursuing, but I hit a wall trying to add the DataColumn to the DataRow. I don't know of a DataRow method that does this.

That left me with the impression that adding columns to the row was implicit by setting the value, that's why I thought

Code:

newRow.Item("myItem") = somevalue

would work.

So now I'm a bit stymied. I know I want to add a new table to my dataset. Is there a resource out there?

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In God we trust, everything else we test.

bmains · September 27th, 2004, 09:40 AM

Hey,

You have to do Dim newRow As DataRow = objTable.NewRow()

The New constructor on DataRow is protected, and therefore cannot be set. You have to use DataTable.NewRow() method. Also, add columns to the DataTable through DataTable.Columns.Add() method.

Then add the table to the dataset by passing the object reference, not just the name:

objDS.Tables.Add(objTable)

Brian

Colonel Angus · September 27th, 2004, 09:44 AM

Thank you both! I found a good reference at http://msdn.microsoft.com/library/de...classtopic.asp

I think it corroborates both your comments.

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In God we trust, everything else we test.

Colonel Angus · September 27th, 2004, 02:06 PM

Just an FYI, here's what I have working:

Code:

Dim myTable As DataTable = New DataTable("myTable")
Dim myCol As DataColumn = avgOneTime.Columns.Add("myCol")

Dim newRow = avgOneTime.NewRow()
newRow.Item("myCol") = somevalue
avgOneTime.Rows.Add(newRow)

dsResult.Tables.Add(myTable)

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In God we trust, everything else we test.

bmains · September 27th, 2004, 02:22 PM

Note that you don't have to receive the DataColumn reference using a DataColumn variable, but you can if you need to. I just said that because I saw you passing it to a variable but don't see it used anywhere.

Brian