Java JPA FetchType.EAGER不起作用 [英] Java JPA FetchType.EAGER does not work
问题描述
我正在使用JPA在Java EE(Jersey)中创建一个应用程序,其中的未初始化实体存在问题.我有3个实体,汽车,所有者,房屋,其中汽车可以有多个所有者,所有者可以有多个房屋.当我返回(entityManager.find)汽车时,所有者将被初始化.当我返回房屋时,将初始化所有者,但不会初始化汽车.我希望能够调用诸如House.getOwner().getCar().getId()之类的东西.现在,我必须在House上致电find,然后在Owner上致电find以获得Car.我该如何解决?
I'm making an application in Java EE (Jersey) with JPA where I have a problem with the uninitialized entities. I have 3 entities Car, Owner, House where the car can have multiple owners and owners can have multiple houses. When i return (entityManager.find) Car then owner is initialized. When i return House then Owner is initialized, but Car is not. I would like to be able to call something like House.getOwner().getCar().getId(). Now I must call find on House and then call find on Owner to get Car. How do I resolve this?
@Entity
@Table(name = "House")
public class HouseEntity {
@Id
@Column(name = "id")
@GeneratedValue(strategy = GenerationType.IDENTITY)
private long id;
@ManyToOne(fetch = FetchType.EAGER)
@JoinColumn(name = "owner_id", nullable = false)
private OwnerEntity owner;
}
@Entity
@Table(name = "Owner")
public class OwnerEntity {
@Id
@Column(name = "id")
@GeneratedValue(strategy = GenerationType.IDENTITY)
private long id;
@ManyToOne(fetch = FetchType.EAGER)
@JoinColumn(name = "car_id")
private CarEntity car;
@OneToMany(mappedBy = "owner")
@JoinColumn(name = "house", nullable = false)
private Set<HouseEntity> house;
}
@Entity
@Table(name = "Car")
public class CarEntity {
@Id
@Column(name = "id")
@GeneratedValue(strategy = GenerationType.IDENTITY)
private long id;
@OneToMany(mappedBy = "owner")
private Set<OwnerEntity> owner;
}
Edit1:对不起,映射中有错误,类运行良好.但是初始化问题仍然存在.
Sorry there was mistake in mapping, classes working well. But problem with initialization remains.
推荐答案
尝试一下:
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;
@Entity
@Table(name = "House")
public class HouseEntity {
@Id
@Column(name = "id")
@GeneratedValue(strategy = GenerationType.AUTO)
private long id;
@ManyToOne
@JoinColumn(name = "owner_id", nullable = false)
private OwnerEntity owner;
public long getId() {
return id;
}
public void setId(long id) {
this.id = id;
}
public OwnerEntity getOwner() {
return owner;
}
public void setOwner(OwnerEntity owner) {
this.owner = owner;
}
}
import java.util.Set;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.OneToMany;
import javax.persistence.Table;
@Entity
@Table(name = "Owner")
public class OwnerEntity {
@Id
@Column(name = "id")
@GeneratedValue(strategy = GenerationType.AUTO)
private long id;
@ManyToOne
@JoinColumn(name = "car_id")
private CarEntity car;
@OneToMany(mappedBy = "owner", fetch = FetchType.EAGER)
private Set<HouseEntity> houses;
public long getId() {
return id;
}
public void setId(long id) {
this.id = id;
}
public CarEntity getCar() {
return car;
}
public void setCar(CarEntity car) {
this.car = car;
}
public Set<HouseEntity> getHouses() {
return houses;
}
public void setHouses(Set<HouseEntity> houses) {
this.houses = houses;
}
}
import java.util.Set;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;
@Entity
@Table(name = "Car")
public class CarEntity {
@Id
@Column(name = "id")
@GeneratedValue(strategy = GenerationType.AUTO)
private long id;
@OneToMany(mappedBy = "car", fetch = FetchType.EAGER)
private Set<OwnerEntity> owner;
public long getId() {
return id;
}
public void setId(long id) {
this.id = id;
}
public Set<OwnerEntity> getOwner() {
return owner;
}
public void setOwner(Set<OwnerEntity> owner) {
this.owner = owner;
}
public void addOwner(OwnerEntity owner){
this.owner.add(owner);
}
}
当您提取Car时,将填充整个对象图.
When you fetch for Car entire object graph will be populated.
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