Hello, can someone help me with this, I am trying to follow this post
http://code.google.com/appengine/docs/java/datastore/relationships.html
to
create relationship between LINKS and TAGS.
I am getting an error:
Caused by:
java.lang.NullPointerException
at com.linkytty.Linkstore.addNewTag(Linkstore.java:101)
at com.linkytty.TagLinker.doPost(TagLinker.java:52)
This happens when I try to add a key using ".add()" :
public void addNewTag(Key tagKey) {
selectedTags.add(tagKey);
}
addNewTag() is called from my
PersistenceManager pm = PMF.get().getPersistenceManager();
Linkstore linkObject = pm.getObjectById(Linkstore.class, objectKey);
linkObject.addNewTag(objectKey);
I've logged my "objectKey" and etc. and it seems that it gets those
right
(
String linkKeyId = req.getParameter("key");
linkKeyID : aghsaW5reXR0eXIPCxIJTGlua3N0b3JlGAUM
Key objectKey = KeyFactory.stringToKey(linkKeyId);
objectKey: Linkstore(5)
)
My Classes:
the class that creates links:
public class Linkstore {
@PrimaryKey
@Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
private Key linkid;
@Persistent(defaultFetchGroup = "true")
private Set<Key> selectedTags;
//STUFF HERE
public Linkstore(User author, String linkcontent, String linkcomment,
Date
date) {
this.author = author;
this.linkcontent = linkcontent;
this.linkcomment = linkcomment;
this.date = date;
selectedTags = new HashSet<Key>();
}
public Key getId() {
return linkid;
}
public String getKeyAsString() {
if (linkid == null)
return null;
return KeyFactory.keyToString(linkid);
}
// STUFF HERE
public void addNewTag(Key tagKey) {
selectedTags.add(tagKey);
}
}
The class that captures the post:
public void doPost(HttpServletRequest req, HttpServletResponse resp)
throws IOException {
String linkKeyId = req.getParameter("key");
Key objectKey = KeyFactory.stringToKey(linkKeyId);
String tagStringKey = req.getParameter("tagkey");
Key tagObjectKey = KeyFactory.stringToKey(tagStringKey);
PersistenceManager pm = PMF.get().getPersistenceManager();
Linkstore linkObject = pm.getObjectById(Linkstore.class,
objectKey);
linkObject.addNewTag(objectKey);
resp.sendRedirect("/");
}
///
Does the "@Persistent(defaultFetchGroup = "true")" make any
difference?
Help & Thanks!
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