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    <p>I hope I understand the question correctly - you want to implement a news feed into your application and allow users to follow each other. The new followers need to be able to see the users actions. I am sure there are multiple other ways of solving this problem, but I will attempt to help you out by providing a solution that makes use of JAVA JDO to access the datastore. </p> <p>I would first design the <a href="https://developers.google.com/appengine/docs/java/datastore/jdo/relationships" rel="nofollow">entity relationships in JDO</a> as follows: </p> <pre><code>1 User to many actions. 1 User to many followers (User). 1 User to many following (User). </code></pre> <p>Here are simple JDO classes:</p> <p>User Class:</p> <pre><code>@PersistenceCapable(identityType=IdentityType.APPLICATION) public class User { @PrimaryKey @Persistent(valueStrategy=IdGeneratorStrategy.IDENTITY) private Key key; @Persistent private String userId; // Google unique user ID, could also store user email. @Persistent private Set&lt;Key&gt; actions; @Persistent private Set&lt;Key&gt; followers; @Persistent private List&lt;Key&gt; following; public User(Key key, String userId) { this.key = key; this.userId = userId; this.actions = new HashSet&lt;Key&gt;(); this.followers = new HashSet&lt;Key&gt;(); this.following = new HashSet&lt;Key&gt;(); } public Key getKey() { return this.key; } public void addAction(Key actionKey) { this.actions.add(actionKey); } public void addActions(Set&lt;Key&gt; actionKeys) { this.actions.addAll(actionKeys); } public Set&lt;Key&gt; getActions() { return this.actions; } public void addFollower(Key followerKey) { this.followers.add(followerKey); } public void addFollowers(Set&lt;Key&gt; followerKeys) { this.followers.addAll(followerKeys); } public Set&lt;Key&gt; getFollowers() { return this.followers; } public void addFollowing(Key followingKey) { this.following.add(followingKey); } public void addAllFollowing(Set&lt;Key&gt; followingKeys) { this.following.addAll(followingKeys); } public Set&lt;Key&gt; getFollowing() { return this.following; } } </code></pre> <p>Action Class:</p> <pre><code>@PersistenceCapable(identityType=IdentityType.APPLICATION) public class Action { @PrimaryKey @Persistent(valueStrategy=IdGeneratorStrategy.IDENTITY) private Key key; @Persistent Date date; @Persistent private String title; public Action(Key key, String title) { this.key = key; this.title = title; this.date = new Date(); // date of creation (now). } public Key getKey() { return this.key; } public void setTitle(String title) { this.title = title; } public String getTitle() { return this.title; } } </code></pre> <p>The Action class makes use of a Date property, you can refer to the <a href="https://developers.google.com/appengine/docs/java/datastore/entities#Java_Properties_and_value_types" rel="nofollow">documentation</a> for applicable data types in the datastore. When an action is created, <a href="http://docs.oracle.com/javase/6/docs/api/java/util/Date.html" rel="nofollow">a Date object is allocated and initialized so that it represents the time at which it was allocated, measured to the nearest millisecond</a>.</p> <p>In my example above I linked the entities by their Keys, you could instead link them by their classes as follows:</p> <pre><code>List&lt;Action&gt; actions; </code></pre> <p>The relationship in my example is one of an unowned one-to-many relationship, perhaps it should be owned one-to-many. More information <a href="https://developers.google.com/appengine/docs/java/datastore/jdo/relationships" rel="nofollow">here</a> for your to take a look and perhaps decide which would be best for your solution.</p> <p>Once the relationships have been defined, you can <a href="https://developers.google.com/eclipse/docs/endpoints-addentities" rel="nofollow">create your endpoint classes around the JDO model classes</a>. This will create basic api methods. You might want to change the endpoint class methods to suit your needs, for example change the way an action is created. A basic example would be to create the key from the actions title as follows (ActionEnpoint.java):</p> <pre><code>... @ApiMethod(name = "insertAction") public Action insertAction( @Named("title") String title ) { PersistenceManager pm = getPersistenceManager(); Key key = KeyFactory.createKey(Action.class.getSimpleName(), title); Action action = null; try { action = new Action(key, title); pm.makePersistent(action); } finally { pm.close(); } return action; } ... </code></pre> <p>If you want to, you can add a method to your UserEndpoint class to query the datastore and return all actions belonging to that user and per date using the <a href="https://developers.google.com/appengine/docs/java/datastore/jdo/queries" rel="nofollow">datastore query objects</a>. </p> <p>You need to add a method to your UserEndpoint class that allows you to add an action to that user, here is a simple example:</p> <pre><code>... @ApiMethod(name = "addActionToUser") public Achiever addActionToUser( @Named("userId") String userId, @Named("actionTitle") String actionTitle) { PersistenceManager pm = getPersistenceManager(); Key userKey = KeyFactory.createKey(User.class.getSimpleName(), userId); Key actionKey = KeyFactory.createKey(Action.class.getSimpleName(), actionTitle); User user = null; try { user = (User) pm.getObjectById(User.class, userKey); user.addAction(actionKey); pm.makePersistent(user); } catch (Exception e) { } return user; } ... </code></pre> <p>Once all of the above is complete you can easily get the list of actions per user by calling the getUser method in your UserEndpoint class, which returns a User object. You can then call [ReturnedUserObject].getActions(). A new follower can now view all of the "followees" actions by just calling the api method to get that "followees" object and get his/her actions. You can then just sort the actions by date or however you envision it.</p> <p>I hope I understood your question correctly, I was unsure about the first component you mentioned, but it seemed as though you got your relationships mixed up. I hope this solution points you in the right direction at least :).</p> <p>If you need any additional help or clarification, or my answer was completely off point to what you were looking for then please let me know. </p> <p>Kind regards, Miki</p>
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    1. POImplementing news feed on GAE - Should I use Prospective Search?
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    1. CO@Miki First of all thank you for the detailed answer. Secondly, the main issue here was not putting the data into the datastore but querying for it in a way that i will not have to fetch EVERYTHING in one batch. Meaning, using cursors. So, just in case i missed something in your answer, can you tell me how do you query "followees" actions (sorted by date) and using a cursor ?
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    2. CO@AsafK Ah, I understand, I apologise, I did not mean to sound condescending, after re-reading your question it makes sense that you have already been storing data properly :). Regardless, in the generated endpoint classes, there should be an api method that will list your data (listUser or listAction). The method takes two parameters, a cursorString and an integer limit. The method returns a list of actions (or users) by making use of a cursor. You should also be able to query by date, I have never done this before but take a look at the docs on querying datastore for more info :).
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    3. CO@Miki As i said in my question, 'IN' query in GAE datastore cannot use cursors. see [documentation](https://developers.google.com/appengine/docs/java/datastore/queries#Java_Limitations_of_cursors). And a query to fetch all "followees" action need to use 'IN'.
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