Hibernate 2.1.2, Spring 1.0.RC1, MSSQLServer, JDK 1.4.2_01.

If I have a domain class like

public class Vacation{
private int visitNumber;
Collection places; // Place
}


public class Place{
private Country belongsTo;
private String description;
private int daysStayed;
}

The country class is mapped to an "immutable" lookup table.
public class Country{
private String id;
private String name;
}


I have mapped Vacation to have a set of Place objects.
I have mapped Country as a many-to-one class within Place with Cascade='none'. This is because Country table is a lookup table that can never be modified from the Place class.

When I try to persist Vacation object, I get
net.sf.hibernate.TransientObjectException: object references an unsaved transient instance - save the transient instance before flushing: Country

I believe I might be using the many-to-one in the wrong context here since my Country object is supposed to be immutable.
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Are there any alternatives other than refactoring Place class like
public class Place{
private String countryID;
private String description;
private int daysStayed;
}
and removing the many-to-one mapping in Place to the Country class.
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Thanks
Madhu