Check for column name in a SqlDataReader object

public static class DataRecordExtensions
{
    public static bool HasColumn(this IDataRecord dr, string columnName)
    {
        for (int i=0; i < dr.FieldCount; i++)
        {
            if (dr.GetName(i).Equals(columnName, StringComparison.InvariantCultureIgnoreCase))
                return true;
        }
        return false;
    }
}

Using Exceptions for control logic like in some other answers is considered bad practice and has performance costs. It also sends false positives to the profiler of # exceptions thrown and god help anyone setting their debugger to break on exceptions thrown.

GetSchemaTable() is also another suggestion in many answers. This would not be a preffered way of checking for a field's existance as it is not implemented in all versions (it's abstract and throws NotSupportedException in some versions of dotnetcore). GetSchemaTable is also overkill performance wise as it's a pretty heavy duty function if you check out the source.

Looping through the fields can have a small performance hit if you use it a lot and you may want to consider caching the results.

It's much better to use this boolean function:

r.GetSchemaTable().Columns.Contains(field)

One call - no exceptions. It might throw exceptions internally, but I don't think so.

NOTE: In the comments below, we figured this out... the correct code is actually this:

public static bool HasColumn(DbDataReader Reader, string ColumnName) { 
    foreach (DataRow row in Reader.GetSchemaTable().Rows) { 
        if (row["ColumnName"].ToString() == ColumnName) 
            return true; 
    } //Still here? Column not found. 
    return false; 
}

In one line, use this after your DataReader retrieval:

var fieldNames = Enumerable.Range(0, dr.FieldCount).Select(i => dr.GetName(i)).ToArray();

Then,

if (fieldNames.Contains("myField"))
{
    var myFieldValue = dr["myField"];
    ...

Edit

Much more efficient one-liner that does not requires to load the schema:

var exists = Enumerable.Range(0, dr.FieldCount).Any(i => string.Equals(dr.GetName(i), fieldName, StringComparison.OrdinalIgnoreCase));