Accessing the List-Property of a DataColumnCollection of a DataTable

Question

I am trying to access the List-Property of the DataColumnCollection of a DataTable, and it seems like there is none. The access is necessary, for there is a collection of strings ("Format") that I need to process after the extraction from the DataTable.

The documentation of Microsoft says, that it is accessible via the Columns of the DataTable (https://learn.microsoft.com/en-us/dotnet/api/system.data.datatable?view=net-6.0), but it isn't.

foreach (object item in dataTable.Columns.List)  // .List is marked as error
{
    Console.WriteLine("TEST: " + item.Format);   // .Format (is string) is marked as error
}

I know that the List-Property is at least getable and that's all I need. I believe that I'm missing something very obvious here... any Ideas?

Object doesn't have a format property. Use var instead of object, then item will have the actual type of what is in dataTable.Columns.List. — Palle Due, Dec 21 '21 at 11:02

Pankaj · Answer 1 · 2021-12-21T11:05:50.690

1

DataColumnCollection is derived from InternalDataCollectionBase which itself is a collection, so your dataTable.Columns themselves is a list, you don't need to do columns.List

This is how you can access the properties of each column.

DataColumnCollection columns = table.Columns;

// Get the ColumnName and DataType for every column.
foreach(DataColumn dataColumn in columns)
{
    Console.WriteLine(dataColumn.ColumnName);
    Console.WriteLine(dataColumn.DataType);
}

edited Dec 21 '21 at 11:05

answered Dec 21 '21 at 11:00

Pankaj

2,618
3
25
47

1

Probably easier to say "because the class is a microsoft one with a name that ends in Collection, it should have an enumerator.." - because these classes are ooooold and implemen t IEnumerable, not IEnumerable they give their elements out as objects, and the compiler writes a cast when it munges the foreach into the iterating expression.. Which is why `foreach(var x in datatable.Columns)` doesn't work immediately (x becomes object and must be cast) – Caius Jard Dec 22 '21 at 12:43

score 0 · Answer 2 · edited Dec 21 '21 at 15:49

0

Try to use linq

var dtColumn = from item in dataTable.Columns.Cast<DataColumn>()
select item.ColumnName;

edited Dec 21 '21 at 15:49

Pablo Claus

5,886
3
29
38

answered Dec 21 '21 at 11:23

sandeepjersey10061990

19
2

Ugh, this really doesn't need LINQ – Caius Jard Dec 22 '21 at 12:35
(but it'd be reasonably expected to work if a DataColumn had a Format property) – Caius Jard Dec 22 '21 at 12:47

score 0 · Answer 3 · answered Dec 22 '21 at 12:33

0

It looks like I found the Answer:

foreach (TableColumn item in dataTable.Columns) 
{
    Console.WriteLine("TEST: " + item.Format);  
}

Seems like the type TableColumn inherits from DataColumn and the property Format can be directly accessed.

answered Dec 22 '21 at 12:33

Nepomuk

21
4

This will work if the datatable.Columns collection does contain a TableColumn instance (whatever that is; neither the DocumentFormat.OpenXml.Spreadsheet.TableColumn, nor System.Windows.Documents.TableColumn seem to inherit from DataColumn, nor do they contain a Format property).. – Caius Jard Dec 22 '21 at 12:41
Incidentally, without knowing that you've filled your datatable with some unknown type TableColumn which has a Format, we wouldn't have been able to arrive at a helpful answer.. If you do stuff that's non-standard, let us know so we can target the advice – Caius Jard Dec 22 '21 at 12:46
1

Will do @CaiusJard. I wasn't aware that it would be non-standard. Thx for contributing. – Nepomuk Dec 23 '21 at 09:47

Accessing the List-Property of a DataColumnCollection of a DataTable

3 Answers3