Using Collections

Morphia supports collections (List, Set, Map) and arrays (Integer).

...

private Set<String> tags;

private Map<String,Translation> translations;

@Reference
private List<Article> relatedArticles;
...

Morphia will use the following implementations (by default) when creating collections:

• java.util.ArrayList for List
• java.util.HashSet for Set
• java.util.HashMap for Map

If you want to use another implementation, you can override this on the annotations:

...
@Property(concreteClass = java.util.TreeSet.class)
private Set<String> tags;

@Embedded(concreteClass = java.util.TreeMap.class)
private Map<String,Translation> translations;

@Reference(concreteClass = java.util.Vector.class)
private List<Article> relatedArticles;
...