datanucleus/JDO

Andy, thank you for your support.
Your response reassured me that my code should have worked. I found my mistake.
Here is what you requested.

@PersistenceCapable(detachable = "true", table = "message")
@DatastoreIdentity(strategy = IdGeneratorStrategy.IDENTITY)
@Inheritance(strategy = InheritanceStrategy.NEW_TABLE)
public class Message {
    @PrimaryKey
    @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
    protected Long messageId = null;
    @Persistent
    @Column(name = "displayName", jdbcType = "VARCHAR", length = 20)
    private String displayName = null;
    @Persistent
    @Column(name = "inputText", jdbcType = "VARCHAR", length = 1200)
    private String inputText = "";
    public Message() {}
    public Message(String displayName, String inputText) {
        this.displayName = displayName;
        this.inputText = inputText;
    }
//... setters and getters here
    @Override
    public String toString() {
        return "messageId is " + getMessageId();
    }
    public boolean equals(Message other) {
        return this.messageId == other.messageId;
    }
    public int hashCode() {
        return this.messageId.intValue();
    }
}

and

    Query<Entry> q = pm.newQuery("select from myDomain.Message where :names.contains(displayName)");
    q.declareParameters("java.util.Set names");
    Collection<Message> collection = (Collection<Message>) q.execute(names);

which gave me
javax.jdo.JDOUserException: Explicit parameters defined for query, yet implicit parameter syntax (":names") found
As you probably already know, if I remove
q.declareParameters("java.util.Set names");
then the exception goes away.
Now, I am using

    tx.begin();
    Query<Message> q = pm.newQuery("select from myDomain.Message where :names.contains(displayName)");
    Collection<Message> collection = (Collection<Message>) q.execute(names);
    messageCollection = (Collection<Message>)pm.detachCopyAll(collection);
    q.closeAll();
    tx.commit();

Thanks again.