Check if column exists when iterating datatable?

Question

I'm taking a datatable and serializing it as geojson. I'm using linq for this:

var envelope = new
{
    type = "FeatureCollection",
    features = dataTable.AsEnumerable().Select(record => new {
        type = "Feature",
        properties = new
        {
            Name = Convert.ToString(record["Name"]),
            Date = Convert.ToString(record["Date"]),
            Icon = Convert.ToString(record["imageUrl"]),
            //ReportMonth = Convert.ToString(record["Month"]),
            ReportMonth = (!string.IsNullOrEmpty(record["Month"])) ? Convert.ToString(record["ReportMonth"]) : string.Empty
        },
        geometry = new
        {
            type = "Point",
            coordinates = new[] {
                Convert.ToDecimal(record["Lon"]),
                Convert.ToDecimal(record["Lat"])
            }
        }
    }).ToArray()
};

This works when the datatable has all the columns. When the column doesn't exist in the datatable (ie. column Month) then the iteration fails.

Is there a way to check if the column exists? I tried using a ternary operator to check the value, but it obviously won't work since I'm still checking if the value exists.

Wouldn't I have to use `DataColumnCollection` for something like this `DataColumnCollection columns = dataTable.Columns; `? — fdkgfosfskjdlsjdlkfsf, Nov 04 '19 at 22:49
Possible duplicate of [ADO.NET DataRow - check for column existence](https://stackoverflow.com/questions/970985/ado-net-datarow-check-for-column-existence) — , Nov 04 '19 at 22:53
It doesn't build if I add it as part of `AsEnumerable().Select`. — fdkgfosfskjdlsjdlkfsf, Nov 04 '19 at 22:57

score 1 · Accepted Answer · 2019-11-05T00:15:38.730

1

You can use:

ReportMonth = record.Table.Columns.Contains("Month") 
            ? Convert.ToString(record["Month"])
            : string.Empty;

Convert.ToString(object) returns string.Empty if the object is null so we don't need to check it.

Here is a speed performance optimization:

bool hasName = dataTable.Columns.Contains("Name");
bool hasDate = dataTable.Columns.Contains("Date");
bool hasimageUrl = dataTable.Columns.Contains("imageUrl");
bool hasMonth = dataTable.Columns.Contains("Month");
bool hasLon = dataTable.Columns.Contains("Lon");
bool hasLat = dataTable.Columns.Contains("Lat");

var envelope = new
{
  // use: ReportMonth = hasMonth ? ... : ... ;
}

edited Nov 05 '19 at 00:15

answered Nov 04 '19 at 22:56

This will iterate the datatable multiple times, not a good solution inside linq statement. Why not use the datarow object you have? Also an explanation of the actual issue the OP is having would be nice as well. – Trevor Nov 04 '19 at 23:07
And for every record in that table your doing a lookup, hence why i said its not a good solution. You don't need to lookup everytime, only one time is needed. – Trevor Nov 04 '19 at 23:16
Indeed, we can check before the query to initialize some booleans if afraid of speed performance. – Nov 04 '19 at 23:18

score 0 · Answer 2 · answered Nov 04 '19 at 23:00

0

You could try record.Table.Columns.Contains(...).

answered Nov 04 '19 at 23:00

tymtam

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Check if column exists when iterating datatable?

2 Answers2