This is part of the FAQs

If your entity uses a backing field for a property, or some other non-standard design, then you can map it using the Access property.

// model public class Account { private IList<Customer> customers = new List<Customer>(); public IList<Customer> Customers { get { return customers; } } } // mapping HasMany(x => x.Customers) .Access.CamelCaseField(); 

The Access property can be used to set various combinations of Field and Property, with various casings and prefixes.

For example, for the same mapping but with the field called _customers you could use the Prefix.Underscore overload: Access.CamelCaseField(Prefix.Underscore).