Examples of javax.jdo.Query

javax.jdo.Query
The Query interface allows applications to obtain persistent instances, values, and aggregate data from the data store. The {@link PersistenceManager} is the factory for Query instances. There may be many Query instances associated with a PersistenceManager. Multiple queries might be executed simultaneously by different threads, but the implementation might choose to execute them serially. In either case, the implementation must be thread safe.
There are three required elements in a Query: the class of the results, the candidate collection of instances, and the filter.
There are optional elements: parameter declarations, variable declarations, import statements, ordering and grouping specifications, result and result class, the range of results, and flags indicating whether the query result is unique and whether the query can be modified.
The query namespace is modeled after methods in Java:
- setClass corresponds to the class definition
- declareParameters corresponds to formal parameters of a method
- declareVariables corresponds to local variables of a method
- setFilter and setOrdering correspond to the method body
There are two namespaces in queries. Type names have their own namespace that is separate from the namespace for fields, variables and parameters.
The method setClass introduces the name of the candidate class in the type namespace. The method declareImports introduces the names of the imported class or interface types in the type namespace. Imported type names must be unique. When used (e.g. in a parameter declaration, cast expression, etc.) a type name must be the name of the candidate class, the name of a class or interface imported by method declareImports, or denote a class or interface from the same package as the candidate class.
The method setClass introduces the names of the candidate class fields.
The method declareParameters introduces the names of the parameters. A name introduced by declareParameters hides the name of a candidate class field of the same name. Parameter names must be unique.
The method declareVariables introduces the names of the variables. A name introduced by declareVariables hides the name of a candidate class field if equal. Variable names must be unique and must not conflict with parameter names.
The result of the query by default is a list of result class instances, but might be specified via setResult. The class of the result by default is the candidate class, but might be specified via setResultClass.
A hidden field may be accessed using the 'this' qualifier: this.fieldName.
The Query interface provides methods which execute the query based on the parameters given. They return a single instance or a List of result class instances which the user can iterate to get results. The signature of the execute methods specifies that they return an Object which must be cast to the appropriate result by the user.
Any parameters passed to the execute methods are used only for this execution, and are not remembered for future execution. @version 2.1


  @SuppressWarnings("unchecked")
  public static Tag getByAlias(String alias) {
    initPm();
    Tag tag = null;
    Query query = pm.newQuery(Tag.class);
    query.setFilter("alias==tagAlias");
    query.declareParameters("java.lang.String tagAlias");
    query.setRange(0, 1);
    List<Tag> listResult = (List<Tag>) query.execute(alias);
    if (listResult.size() > 0) {
      tag = listResult.get(0);
    }
    return tag;
  }

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  }
  
  @SuppressWarnings("unchecked")
  public static List<Tag> getTop10View() {
    initPm();
    Query query = pm.newQuery(Tag.class);    
    query.setOrdering("count desc");
    query.setRange(0, 10);
    List<Tag> listResult = (List<Tag>) query.execute();
    return listResult;
  }

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    email.append(user.getLastEmail());
    email.append("\r\n\r\n");
    
    //retrieve subscriptions
    //fetch sub
    Query sq = pm.newQuery(Subscription.class);
    sq.setFilter("userKey == uk && lastDate > date");
    sq.declareParameters("com.google.appengine.api.datastore.Key uk, java.util.Date date");
    
    @SuppressWarnings("unchecked")
    List<Subscription> ls = (List<Subscription>) sq.execute(user.getKey(),user.getLastEmail());
    
    //fetch new subscriptions
    for(Subscription sub : ls){
      //fetch entries
      Query qEntry = pm.newQuery(BlogEntry.class);
      qEntry.setFilter("blogKey == bk && pubDate > date");
      qEntry.declareParameters("com.google.appengine.api.datastore.Key bk, java.util.Date date");
      
      //fetch entries
      List<BlogEntry> entries = (List<BlogEntry>) qEntry.execute(sub.getBlogKey(),user.getLastEmail());
      
      boolean title = false;
      for(BlogEntry entry : entries){
        ismail = true;
        if (!title) {
          title = true;
          email.append("\r\n");
          email.append(entry.getBlogTitle());
          email.append("\r\n");
        }
        email.append(" * ");
        email.append(entry.getTitle());
        email.append("\r\n  ");
        email.append(entry.getLink());
        email.append("\r\n");
      }
      qEntry.closeAll();
    }
    sq.closeAll();
    
    email.append("\r\nClick here to unsubscribe : ");
    email.append(HOST);

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          //bad number
          return;
        }
        
        //find sub
        Query q = pm.newQuery(Subscription.class);
        q.setFilter("userKey == k");
        q.declareParameters("com.google.appengine.api.datastore.Key k");
        
        @SuppressWarnings("unchecked")
        List<Subscription> subs = (List<Subscription>) q.execute(u.getKey());
        int i = 1;
        for(Subscription sub : subs){
          if (nb == i) {
            subToRemove = sub.getKey();
            break;

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  @Override
  public User getUserFromId(PersistenceManager pm , String id){
    User user = null;


    Query q = pm.newQuery(User.class);
    q.setFilter("id == jid");
    q.declareParameters("java.lang.String jid");
    
    @SuppressWarnings("unchecked")
    List<User> list = (List<User>) q.execute(id);
    
    if (list.size() > 0){
      user = list.get(0);
    }
    q.closeAll();
    
    
    return user;
  }

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  @Override
  public Subscription getSubscription(PersistenceManager pm, User user, Blog blog){
    
    Subscription sub = null;


    Query q = pm.newQuery(Subscription.class);
    
    q.setFilter("userKey == uk && blogKey == bk");
    q.declareParameters("com.google.appengine.api.datastore.Key uk , "
        + "com.google.appengine.api.datastore.Key bk");


    @SuppressWarnings("unchecked")
    List<Subscription> list = (List<Subscription>) q.execute(user.getKey(), blog.getKey());
    
    if (list.size() > 0){
      sub = list.get(0);
    }
    q.closeAll();
    q = null;
    
    return sub;
  }

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  @Override
  public Blog getBlogFromLink(PersistenceManager pm , String link){
    Blog blog = null;


    //try direct link
    Query q = pm.newQuery(Blog.class);
    q.setFilter("link == '" + link +"'");
    
    List<Blog> blogs = (List<Blog>) q.execute();
    
    if (blogs.size() > 0){
      blog = blogs.get(0);
    }
    
    //if blog not found, fetch blog by rss
    if (blog == null){
      q = pm.newQuery(Blog.class);
      q.setFilter("rss == '" + link +"'");
      
       blogs = (List<Blog>) q.execute();
      if (blogs.size() > 0){
        blog = blogs.get(0);
      }
    }
    q.closeAll();
    q = null; 
    
    return blog;
  }

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    DataManager dm = DataManagerFactory.getInstance();
    PersistenceManager pm = dm.newPersistenceManager();
    
    User user = dm.getUserFromId(pm , jid);
    
    Query q = pm.newQuery(Subscription.class);
    q.setFilter("userKey == uk");
    q.declareParameters("com.google.appengine.api.datastore.Key uk");
    
    @SuppressWarnings("unchecked")
    List<Subscription> list = (List<Subscription>) q.execute(user.getKey());
    
    for(Subscription s : list){
      pm.currentTransaction().begin();
      s.setLatestEntryNotifiedDate(lastPubDate);
      s.setLastProcessDate(lastProcess);

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    if (jid != null){
      DataManager dm = DataManagerFactory.getInstance();
      PersistenceManager pm = dm.newPersistenceManager();
      
      //fetch user
      Query quser = pm.newQuery(User.class);
      quser.setFilter("id == jid");
      quser.declareParameters("java.lang.String jid");
      quser.setUnique(true);
      
      User user = (User) quser.execute(jid);
      
      if (user != null){
        //fetch all subscriptions
        Query q = pm.newQuery(Subscription.class);
        q.setFilter("userKey == key");
        q.declareParameters("com.google.appengine.api.datastore.Key key");
        
        @SuppressWarnings("unchecked")
        List<Subscription> list = (List<Subscription>) q.execute(user.getKey());
        
        //mark all user's subscription as read (by recent date)
        for(Subscription s : list){
          pm.currentTransaction().begin();
          s.setLatestEntryNotifiedDate(now);

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    PersistenceManager pm = dm.newPersistenceManager();
    
    //fetch user
    User u = dm.getUserFromId(pm , id);
    
    Query q = pm.newQuery(Subscription.class);
    q.setFilter("userKey == k");
    q.declareParameters("com.google.appengine.api.datastore.Key k");
    
    @SuppressWarnings("unchecked")
    List<Subscription> subs = (List<Subscription>) q.execute(u.getKey());
    
    int n = 0;
    StringBuilder sb = new StringBuilder();
    for(Subscription s : subs){
      Blog b = pm.getObjectById(Blog.class, s.getBlogKey());

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