Nesting Tables in WordProcessing

Whenver I try and nest tables in a new Wordprocessing Document, the file won't open.  Here is a basic example of what I'm trying to accomplish

 Using wordDoc As WordprocessingDocument = WordprocessingDocument.Create("C:\Integration\Nested.docx", DocumentFormat.OpenXml.WordprocessingDocumentType.Document)
 '---- Create Main Document
 Dim mainDocument As MainDocumentPart = wordDoc.AddMainDocumentPart()
 mainDocument.Document = New DocumentFormat.OpenXml.Wordprocessing.Document()
 Dim body As New DocumentFormat.OpenXml.Wordprocessing.Body()
 
 '--- Create Parent Table
 Dim tbl1 As New DocumentFormat.OpenXml.Wordprocessing.Table
 Dim row1 As New DocumentFormat.OpenXml.Wordprocessing.TableRow
 Dim col1 As New DocumentFormat.OpenXml.Wordprocessing.TableCell(New DocumentFormat.OpenXml.Wordprocessing.Paragraph)

 '--- Create Nested Table
 Dim tbl2 As New DocumentFormat.OpenXml.Wordprocessing.Table
 Dim row2 As New DocumentFormat.OpenXml.Wordprocessing.TableRow
 Dim col2 As New DocumentFormat.OpenXml.Wordprocessing.TableCell(New DocumentFormat.OpenXml.Wordprocessing.Paragraph(New DocumentFormat.OpenXml.Wordprocessing.Run(New DocumentFormat.OpenXml.Wordprocessing.Text("Test"))))

 '--- Add Cell and Row to Nested Table
 row2.Append(col2)
 tbl2.Append(row2)
 
 '--- Add Nested Table to Parent Cell
 col1.Append(tbl2)
 
 '--- Add Cell and Row to Parent Table
 row1.Append(col1)
 tbl1.Append(row1)
 
 '--- Add Parent Table to Body
 body.Append(tbl1)
 
 '--- Add Body to Document and Save
 mainDocument.Document.Append(body)
 mainDocument.Document.Save()
End Using

I'm not sure, but I would guess that the main document part isn't enough. Try to figure out which parts need also to be created in order to create a valid document. Or this happens only when you add a second, nested table inside a cell of the first table?

It only happens when I add a second nested table inside a cell of the first table.  I finally found a solution after searching and a lot of trial and error.  I don't know why this works, but If you append a paragrah after you append the nested table the document opens successfully.

As I know, you cannot have an empty table cell without a paragraph. Still, I would say that having another table inside a parent cell as its only child element wouldn't pose a problem, ... but as you found out it does! I gues it is the same as a blank document - even a blank document starts with a paragraph, otherwise there would be no starting position for the cursor.

If you are doing data driven document generation you might also want to take a look at Docentric toolkit. It is also able to render hierarchical data in the form of n-level nested tables.