Re: [appengine-java] Re: convert JDO query to JPA
This actually makes more sense. JPA does not write to the data store until
either the EntityManager is closed or the transaction is flushed. Here's an
example using transactions:
EntityManager em = EMF.get().createEntityManager();
PrintWriter out = response.getWriter();
ListDog dogs;
try {
Dog newDog = new Dog(New dog!, 1);
EntityTransaction tx = em.getTransaction();
tx.begin();
em.persist(newDog);
tx.commit();
Query query = em.createQuery(SELECT FROM Dog); // WHERE key =
:key);
dogs = (ListDog) query.getResultList();
// etc
Here are some examples:
http://openjpa.apache.org/builds/1.0.2/apache-openjpa-1.0.2/docs/manual/jpa_overview_em_lifeexamples.html
On Mon, Nov 23, 2009 at 8:18 PM, lp lucio.picc...@gmail.com wrote:
EntityManager em = EMF.get().createEntityManager();
PrintWriter out = response.getWriter();
ListDog dogs;
try {
Query query = em.createQuery(SELECT FROM Dog WHERE
dogFriends = :key);
query.setParameter(key, key);
dogs = (ListDog) query.getResultList();
dogs.size(); // Do this so we can eager load the list and
solve it!
running your code in my unit test i still get a 0 size result list.
*until* i added the following in my unittest
Dog user1 = new Dog()
//blah blah
em.merge(user1);
em.close(); -- needed to close existing em
em = getEnityManager();
//query now executes correctly
it seems that the entity manager is not working as i expected.
by doing em.close after making objects persistent and then getting new
em, allowed the em.query to execute correctly.
i am not clear of why the em behaviours like that, given the em.find()
seem to find the correct object.
any ideas?
-lp
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Ikai Lan
Developer Programs Engineer, Google App Engine
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Re: [appengine-java] Re: convert JDO query to JPA
Here's a video from Google I/O last year about complex data modeling on App
Engine. It talks a little bit about how we do indexing underneath the hood:
http://www.youtube.com/watch?v=AgaL6NGpkB8
Look for an upcoming article about the subject. App Engine Datastore is
built on top of BigTable. It's not really voodoo, the properties are
simply indexed. The reason it may seem strange is because coming from an
RDBMS world, this just isn't something that is done. In App Engine, however,
the way indexing works allows us to be flexible in what data types it allows
us to surface and the ways we allow users to query those data types.
Here are my example classes:
Dog.java: http://pastie.org/711953
ListFriendsServlet.java: http://pastie.org/711959
import com.google.appengine.api.datastore.Key;
import javax.persistence.*;
import java.util.List;
import java.util.LinkedList;
@Entity
public class Dog {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Key key;
@Basic
private String name;
@Basic
private int age;
private ListKey dogFriends;
public Dog(String name, int age) {
this.name = name;
this.age = age;
}
public Dog() {
this(Lucky, 5);
}
public Key getKey() {
return key;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public void addDogFriend(Key key){
if (this.dogFriends == null) {
this.dogFriends = new LinkedListKey();
}
this.dogFriends.add(key);
}
public ListKey getDogFriends(){
return this.dogFriends;
}
@Override
public String toString() {
return Dog{ +
key= + key +
, name=' + name + '\'' +
, age= + age +
'}';
}
}
import EMF;
import Dog;
import com.google.appengine.api.datastore.Key;
import com.google.appengine.api.datastore.KeyFactory;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.ServletException;
import javax.persistence.EntityManager;
import javax.persistence.Query;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;
public class ListFriendsServlet extends HttpServlet {
@SuppressWarnings(unchecked)
protected void doGet(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
String keyString = request.getParameter(friend);
Key key = KeyFactory.stringToKey(keyString);
EntityManager em = EMF.get().createEntityManager();
PrintWriter out = response.getWriter();
ListDog dogs;
try {
Query query = em.createQuery(SELECT FROM Dog WHERE
dogFriends = :key);
query.setParameter(key, key);
dogs = (ListDog) query.getResultList();
dogs.size(); // Do this so we can eager load the list and
close the EMF
} finally {
em.close();
}
out.println(Listing dogs);
for(Dog dog : dogs) {
out.println(dog);
}
}
}
The other classes describe adding Dogs and Dog friends and aren't terribly
interesting.
On Sun, Nov 22, 2009 at 2:49 PM, lp lucio.picc...@gmail.com wrote:
Can you post the JPA version of your entity?
@Entity
public class Friend {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Key key;
private String lastName;
public int crud;
private String firstName;
@Basic
private CollectionKey friends;
I've just built something similar, and if I pass a Key to:
query.setParameter(key, key);
This works correctly, though if I pass the String key to it
query.setParameter(key, someLongString);
what was ur query? was the query to filter on a collection?
i have set the parameters against primitive members successfully but
not against collection members.
It returns an empty list. Could this be what is happening?
no.i just retested my code to make sure i hadnt messed up. i am
definitely using a Key not a string.
//JPA
javax.persistence.Query query = em.createQuery(select from Friend f
where f.friends=:key);
query.setParameter(key, user2.getKey());
return list of 0
using the *same* JPA entity code the JDO works fine
//JDO
javax.jdo.Query query = pm.newQuery(Friend.class);
Key myKey = user2.getKey();
query.declareParameters(com.google.appengine.api.datastore.Key
myKey);
query.setFilter(friends == myKey);
query.setOrdering(lastName ASC, firstName ASC);
ListFriend friendList = (ListFriend) query.execute(myKey);
return correct list
Q1 can u post your JPA code so i can see what u have done differently?
Q2. is mixing JPA and JDO
[appengine-java] Re: convert JDO query to JPA
EntityManager em = EMF.get().createEntityManager();
PrintWriter out = response.getWriter();
ListDog dogs;
try {
Query query = em.createQuery(SELECT FROM Dog WHERE
dogFriends = :key);
query.setParameter(key, key);
dogs = (ListDog) query.getResultList();
dogs.size(); // Do this so we can eager load the list and
solve it!
running your code in my unit test i still get a 0 size result list.
*until* i added the following in my unittest
Dog user1 = new Dog()
//blah blah
em.merge(user1);
em.close(); -- needed to close existing em
em = getEnityManager();
//query now executes correctly
it seems that the entity manager is not working as i expected.
by doing em.close after making objects persistent and then getting new
em, allowed the em.query to execute correctly.
i am not clear of why the em behaviours like that, given the em.find()
seem to find the correct object.
any ideas?
-lp
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[appengine-java] Re: convert JDO query to JPA
EntityManager em = EMF.get().createEntityManager();
PrintWriter out = response.getWriter();
ListDog dogs;
try {
Query query = em.createQuery(SELECT FROM Dog WHERE
dogFriends = :key);
query.setParameter(key, key);
dogs = (ListDog) query.getResultList();
dogs.size(); // Do this so we can eager load the list and
solve it!
running your code in my unit test i still get a 0 size result list.
*until* i added the following in my unittest
Dog user1 = new Dog()
//blah blah
em.merge(user1);
em.close(); -- needed to close existing em
em = getEnityManager();
//query now executes correctly
it seems that the entity manager is not working as i expected.
by doing em.close after making objects persistent and then getting new
em, allowed the em.query to execute correctly.
i am not clear of why the em behaviours like that, given the em.find()
seem to find the correct object.
any ideas?
-lp
--
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[appengine-java] Re: convert JDO query to JPA
Can you post the JPA version of your entity?
@Entity
public class Friend {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Key key;
private String lastName;
public int crud;
private String firstName;
@Basic
private CollectionKey friends;
I've just built something similar, and if I pass a Key to:
query.setParameter(key, key);
This works correctly, though if I pass the String key to it
query.setParameter(key, someLongString);
what was ur query? was the query to filter on a collection?
i have set the parameters against primitive members successfully but
not against collection members.
It returns an empty list. Could this be what is happening?
no.i just retested my code to make sure i hadnt messed up. i am
definitely using a Key not a string.
//JPA
javax.persistence.Query query = em.createQuery(select from Friend f
where f.friends=:key);
query.setParameter(key, user2.getKey());
return list of 0
using the *same* JPA entity code the JDO works fine
//JDO
javax.jdo.Query query = pm.newQuery(Friend.class);
Key myKey = user2.getKey();
query.declareParameters(com.google.appengine.api.datastore.Key
myKey);
query.setFilter(friends == myKey);
query.setOrdering(lastName ASC, firstName ASC);
ListFriend friendList = (ListFriend) query.execute(myKey);
return correct list
Q1 can u post your JPA code so i can see what u have done differently?
Q2. is mixing JPA and JDO ok? ie. JPA entity and JDO seems to work for
me.
Q3.how does the collection equality filter work in app engine? I have
not found any docs to explain the 'voodoo' like behaviour.
from what i can determine the collection filter is executed on the
data store and not in the application as the unfiltered list executed
the 1000 row limit.
it works but i dont understand how.
any help most appreciated
-lp
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[appengine-java] Re: convert JDO query to JPA
Q2. is mixing JPA and JDO ok? ie. JPA entity and JDO seems to work for me. As per the DataNucleus docs you can define persistence with JPA metadata and persist using JDO, or define persistence using JDO metadata and persist using JPA. You definitely won't find that flexibility in any other JPA/JDO implementation. Q3.how does the collection equality filter work in app engine? I have not found any docs to explain the 'voodoo' like behaviour. I assume their interpretation of field == collectionValue is the same as collectionValue.contains(field) i.e non-standard JDOQL. When they support valid JDOQL syntax (the latter expression, in their next release IIRC) you would be strongly recommended to change to use that rather than this weirdness -- You received this message because you are subscribed to the Google Groups Google App Engine for Java group. To post to this group, send email to google-appengine-j...@googlegroups.com. To unsubscribe from this group, send email to google-appengine-java+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-appengine-java?hl=.
