I have three pojo
class Theme {
private Integer themeId;
.....
private Set<ThemeSectorMap> themeSectors;
}
class Sector{
private Integer sectorId;
private Set<ThemeSectorMap> sectorThemes;
}
class ThemeSectorMap{
private Integer themeSectorMapId
private Theme theme;
private Sector sector;
private User creator;
private Date creationDate;
.....
}

In Mapping file of Theme I mapped the Set<ThemeSectorMap> as:
<set name="themeSector" table="theme_sector_map" cascade="all" lazy ="true" >
<key>
<column name="theme_id" />
</key>
<one-to-many class="com.ogs.model.ThemeSectorMap" />
</set>

When I add theme object, it insert theme and its mapping also when it provide.
But when I update theme and remove any object from set of themeSectors,
it set null theme_id (reference column) in corresponding record.
I want remove whole mapping record from database.

Please give suggestions.