Examples of com.db4o.query.Query

com.db4o.query.Query
handle to a node in a S.O.D.A. query graph.

A node in the query graph can represent multiple classes, one class or an attribute of a class.

The graph is automatically extended with attributes of added constraints (see {@link #constrain(Object)}) and upon calls to {@link #descend(java.lang.String)} that request nodes that do not yet exist.

References to joined nodes in the query graph can be obtained by "walking" along the nodes of the graph with the method {@link #descend(String)}.

{@link #execute()}evaluates the entire graph against all persistent objects.

{@link #execute()} can be called from any {@link Query} nodeof the graph. It will return an {@link ObjectSet} filled withobjects of the class/classes that the node, it was called from, represents.

Note:
{@link Predicate Native queries} are the recommended main query interface of db4o.

    query.descend("mMessage").constrain(message).identity();
    return new Persistent.InitializingObjectSet<WoTMessageRating>(mFreetalk, query);
  }
  
  public ObjectSet<? extends MessageRating> getAllMessageRatingsBy(OwnIdentity rater) {
    final Query query = db.query();
    query.constrain(WoTMessageRating.class);
    query.descend("mRater").constrain(rater).identity();
    return new Persistent.InitializingObjectSet<WoTMessageRating>(mFreetalk, query);
  }

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    return identity;
  }
  
  public ObjectSet<WoTIdentity> getAllIdentities() {
    Query q = db.query();
    q.constrain(WoTIdentity.class);
    return new Persistent.InitializingObjectSet<WoTIdentity>(mFreetalk, q);
  }

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      fetchOwnIdentities();
      garbageCollectIdentities();
    } 
    catch(Exception e) {} /* Ignore, return the ones which are in database now */
    
    final Query q = db.query();
    q.constrain(WoTOwnIdentity.class);
    return new Persistent.InitializingObjectSet<WoTOwnIdentity>(mFreetalk, q);


  }

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  }


  @SuppressWarnings("unchecked")
  public synchronized WoTIdentity getIdentity(String id) throws NoSuchIdentityException {
    Query q = db.query();
    q.constrain(WoTIdentity.class);
    q.descend("mID").constrain(id);
    ObjectSet<WoTIdentity> result = q.execute();
    
    switch(result.size()) {
      case 1:
        WoTIdentity identity = result.next();
        identity.initializeTransient(mFreetalk);

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    return getIdentity(WoTIdentity.getIDFromURI(uri));
  }
  
  @SuppressWarnings("unchecked")
  public synchronized WoTOwnIdentity getOwnIdentity(String id) throws NoSuchIdentityException {
    Query q = db.query();
    q.constrain(WoTOwnIdentity.class);
    q.descend("mID").constrain(id);
    ObjectSet<WoTOwnIdentity> result = q.execute();
    
    switch(result.size()) {
      case 1:
        WoTOwnIdentity identity = result.next();
        identity.initializeTransient(mFreetalk);

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        // TODO: Maybe handle this in WoT. Would require checks in many places though.
        continue;
      }
      
      synchronized(this) { /* We lock here and not during the whole function to allow other threads to execute */
        Query q = db.query(); // TODO: Encapsulate the query in a function...
        q.constrain(WoTIdentity.class);
        q.descend("mID").constrain(identityID);
        ObjectSet<WoTIdentity> result = q.execute();
        WoTIdentity id = null; 
        
        if(result.size() == 0) {
          try {
            importIdentity(bOwnIdentities, identityID, requestURI, insertURI, nickname, fetchID);

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      if((ownIdentities && mLastOwnIdentityFetchID == 0) || (!ownIdentities && mLastIdentityFetchID == 0))
        return;


      long acceptID = ownIdentities ? mLastOwnIdentityFetchID : mLastIdentityFetchID;


      Query q = db.query();
      if(ownIdentities)
        q.constrain(WoTOwnIdentity.class);
      else {
        q.constrain(WoTIdentity.class);
        q.constrain(WoTOwnIdentity.class).not();
      }
      
      q.descend("mLastReceivedFromWoT").constrain(acceptID).not();
      ObjectSet<WoTIdentity> result = q.execute();


      for(WoTIdentity identity : result) {
        identity.initializeTransient(mFreetalk);
        if(logDEBUG) Logger.debug(this, "Garbage collecting identity " + identity);
        deleteIdentity(identity, messageManager, taskManager);

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        HashSet<String> deleted = new HashSet<String>();


        Logger.debug(this, "Searching for duplicate identities ...");


        for(WoTIdentity identity : getAllIdentities()) {
          Query q = db.query();
          q.constrain(WoTIdentity.class);
          q.descend("mID").constrain(identity.getID());
          q.constrain(identity).identity().not();
          ObjectSet<WoTIdentity> duplicates = new Persistent.InitializingObjectSet<WoTIdentity>(mFreetalk, q);
          
          for(WoTIdentity duplicate : duplicates) {
            if(deleted.contains(duplicate.getID()) == false) {
              Logger.error(duplicate, "Deleting duplicate identity " + duplicate.getRequestURI());

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  // TODO: This function should be a feature of WoT.
  private synchronized void updateShortestUniqueNicknameCache() {
    if(logDEBUG) Logger.debug(this, "Updating shortest unique nickname cache...");
    
    // We don't use getAllIdentities() because we do not need to have intializeTransient() called on each identity, we only query strings anyway.
    final Query q = db.query();
    q.constrain(WoTIdentity.class);
    ObjectSet<WoTIdentity> result = new Persistent.InitializingObjectSet<WoTIdentity>(mFreetalk, q);
    final WoTIdentity[] identities = result.toArray(new WoTIdentity[result.size()]);
    
    Arrays.sort(identities, new Comparator<WoTIdentity>() {

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  private FetcherCommand getCommand(Class<? extends FetcherCommand> commandType, WoTIdentity identity) throws NoSuchCommandException {
    return getCommand(commandType, identity.getID());
  }
  
  private FetcherCommand getCommand(Class<? extends FetcherCommand> commandType, String identityID) throws NoSuchCommandException {
    final Query q = mDB.query();
    q.constrain(commandType);
    q.descend("mIdentityID").constrain(identityID);
    final ObjectSet<FetcherCommand> result = new Persistent.InitializingObjectSet<FetcherCommand>(mFreetalk, q);
    
    switch(result.size()) {
      case 1: return result.next();
      case 0: throw new NoSuchCommandException();

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