how to create CSV string from DataTable in VB.NET? - vb.net

Question

I'm fetching data from database as a DataTable and need to convert into CSV string in VB.NET.

Answer 1

Create a generic method with DataTable, CSV Headers, DataTable Columns parameters:
Private Function CSVBuilder(dt As DataTable, headers As List(Of String), columns As List(Of String)) As String
Dim sCSV = New StringBuilder(String.Join(",", headers))
sCSV.Append(Environment.NewLine)
Dim view As New DataView(dt)
Dim tDt As DataTable = view.ToTable(True, columns.ToArray)
For Each row As DataRow In tDt.Rows
'-- Handle comma
sCSV.Append(String.Join(",", (From rw In row.ItemArray Select If(rw.ToString.Trim.Contains(","), String.Format("""{0}""", rw.ToString.Trim), rw.ToString.Trim))))
sCSV.Append(Environment.NewLine)
Next
Return sCSV.ToString
End Function
And then call in your code to get CSV string:
CSVBuilder(dataTable,
New List(Of String) From {"Header Column 1", "Header Column 2", ...},
New List(Of String) From {"DataTableColumn1", "DataTableColumn2", ...})

Answer 2

In response to the comment, since this wouldn't fit in that space:
Private Function CSVBuilder(dt As DataTable) As String
Dim sCSV As New StringBuilder()
'Headers
Dim delimeter As String = ""
For Each col As String In dt.Columns.Select(Func(col) col.ColumnName)
If col.Contains(",") Then col = """" & col & """"
sCSV.Append(delimeter).Append(col)
delimeter = ","
Next
sCSV.AppendLine()
For Each row As DataRow In tDt.Rows
sCSV.AppendLine(String.Join(",", (From rw In row.ItemArray Select If(rw.ToString.Trim.Contains(","), String.Format("""{0}""", rw.ToString.Trim), rw.ToString.Trim))))
Next
Return sCSV.ToString
End Function
Now, I did remove this code:
Dim view As New DataView(dt)
Dim tDt As DataTable = view.ToTable(True, columns.ToArray)
But I wouldn't do this as part of the CSVBuilder() method. If you want to project a specific view of a table, I would do that separately from creating the CSV data. You could make a separate method for it:
Public Function GetProjection(dt As DataTable, columns As IEnumerable(Of String)) As DataTable
Dim view As New DataView(dt)
Return view.ToTable(True, columns.ToArray())
End Function
And then you call them together like this:
Dim dt As DataTable = '.... original table here
Dim columns() As String = '... the columns you want
Dim csv As String = CSVBuilder(GetProjection(dt, columns))
or like this:
Dim dt As DataTable = '.... original table here
Dim columns() As String = '... the columns you want
Dim dt1 = GetProjection(dt, columns)
Dim csv As String = CSVBuilder(dt1)
This is called Currying, and it's a good thing to do.
Finally, I'll repeat my suggestion to think in terms of writing to a stream. Long strings with repeated append operations can cause real problems for the .Net garbage collector. Using StringBuilder can help, but won't fully eliminate these problems. Writing to a Stream, which is often connected to a file on disk, gives you the opportunity to completely eliminate this issue. Plus, it will likely save you work later on.