GenericAddOrUpdateFromCsv.cs

public void AddOrUpdate<T>(string fileName, params string[] columnNames) where T : class
{
    Console.WriteLine($"AddOrUpdate : {fileName} ");

    var entityRows = new List<T>();

    var csvRows = _csvFileReader.ReadAllRows("DataFiles\\" + fileName);

    foreach (var csvRow in csvRows)
    {
        var instance = (T)Activator.CreateInstance(typeof(T));

        for (int index = 0; index < csvRow.Length; index++)
        {
            var property = instance.GetType().GetProperty(columnNames[index]);

            if (property == null)
            {
                throw new ArgumentNullException($"Property [{columnNames[index]}] not found on type [{instance}]");
            }

            var propertyValue = Cast(property.PropertyType, csvRow[index]);

            property.SetValue(instance, propertyValue);

        }
        entityRows.Add(instance);
    }
    _context.Set<T>().AddOrUpdate(entityRows.ToArray());
    _context.SaveChanges();
}