SqlBulkCopyHelper.cs

    public class SqlBulkCopyHelper
    {
        public static async Task BulkInsert<T>(string connectionString, string tableName, string[] columns, IEnumerable<T> list, string[] ignoredColumns = null)
        {
            using (var connection = new SqlConnection(connectionString))
            {
                using (var bulkCopy = new SqlBulkCopy(connection))
                {
                    await connection.OpenAsync();
                    bulkCopy.BulkCopyTimeout = 300;

                    bulkCopy.DestinationTableName = tableName;
                    var table = new DataTable();

                    if (ignoredColumns == null)
                    {
                        ignoredColumns = new string[] { };
                    }

                    var t = typeof(T);
                    var columnProperties = columns.Select(c =>
                    {
                        var property = t.GetProperty(c, BindingFlags.Instance | BindingFlags.Public);

                        return property;
                    }).ToList();

                    foreach (var column in columnProperties)
                    {
                        table.Columns.Add(column.Name, Nullable.GetUnderlyingType(column.PropertyType) ?? column.PropertyType);
                    }

                    foreach (var item in list)
                    {
                        var values = new object[columnProperties.Count];
                        for (var i = 0; i < columnProperties.Count; i++)
                        {
                            if (ignoredColumns.Contains(columnProperties[i].Name))
                            {
                                continue;
                            }
                            values[i] = columnProperties[i].GetValue(item);
                        }

                        table.Rows.Add(values);
                    }

                    bulkCopy.BatchSize = table.Rows.Count;

                    await bulkCopy.WriteToServerAsync(table);

                }
                connection.Close();
            }
        }
    }