Hibernate-简单查询懒惰获取

Question

I'm using the Play Framework with Hibernate and JPA.

I have a simple entity :

@Entity
public class Player extends Model {

    @Required
    public Long gold;
}

I would like to retrieve all my players, so here is the query I execute using Hibernate :

select p from Player p

The result has been stored in a list : List<Player> and when I want to debug to see what is in the list I can see 104 players, but only the 5 first players of the list are really loaded. Other players are lazy fetched : the class name is something like Player_$$_javassist_22 .

My question is : why aren't all my players entirely loaded? Why some of them are lazy fetched? I would like to have all my players loaded without lazy fetching, how can I do?

Thank you

Answer 1

In a XML hibernate mapping you would simply write: <class name="Player" lazy="false">... which causes your player objects to be fetched eagerly.

With annotations you can do the same using @Proxy(lazy=false) as described here

further information you can find here

Answer 2

您可以在关联上使用@ManyToOne(fetch = FetchType.EAGER)以禁用延迟加载。

Answer 3

first lets understand the concept of 'javax.persistence.FetchType' suppose you have two entities as 'Player' and 'Team' as folows having @oneToMany relationship between them

@Entity
@Table(name = "player")
public class Player extends Model {
    public Long gold;
    String name;    
}

and

@Entity
@Table(name = "team")
public class Team {
    @Column (name = "name") 
    public String name;

    @OneToMany(fetch = FetchType.LAZY,mappedBy="players")
    public List<Player> players;    
}

Now when you load a Team from the database, JPA loads its name field for you. But you have two options for players : to load it together with the rest of the fields (ie eagerly[ FetchType.EAGER ]) or to load it on-demand (ie lazily[ FetchType.LAZY ]) when you call the Teams getPlayers() method.

When a Team has many players it is not efficient to load all of its players with it when they are not needed. So in suchlike cases, you can declare that you want players to be loaded when they are actually needed. This is called lazy loading.

so its up to you which FetchType is suitable for your problem. If you really want to load all players while loading the team then use FetchType.EAGER .

hope this will solve your problem....