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Ecplise JPA添加新的父对象

cascade entity-relationship jpa eclipse java

hong yie Huang · 技术社区 · 7 年前

我正在尝试用Netbean构建一个应用程序。我使用Eclipse IDE&JPA API。实体如下:

纳茨。Java语言

@Entity
@Table(name = "NATS")
Public Class NATS implements Serializable {
  private static final long serialVersionUID = 1L;
  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Integer code;
  private String nName;
  @Column(name = "cap_id") // for foreign key purpose
  private Integer capId;
  @OneToOne(cascade=CascadeType.PERSIST)
  @PrimaryKeyJoinColumn(name = "cap_id" )
  private City capital;
  public City getCapital(){
      return this.capital;
  }
  public void setCapital (City newcapital){
      this.capital = newcapital;
  }
  ... some gets & sets methods
}

城市Java语言

@Entity
public class City implements Serializable {
  private static final long serialVersionUID = 1L;
  private String cityName;    
  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  @Basic(optional = false)
  private Integer cityId;
  public String getCityName() {
      return cityName;
  }
  public void setCityName(String newcityName) {
      this.cityName = newcityName;
  }    
  public City(String ctname) {
      this.cityName = ctname;
  }
  public Integer getcityId() {
      return cityId;
  }
  public void setcityId(Integer ctId) {
      this.cityId = ctId;
  }

}

当我想添加新的NAT对时&城市,我用这个:

一些豆子。Java语言

@Stateless
public class somebean {
  @PersistenceContext(unitName = "TestLocal")
  private EntityManager em;

  public NATs insertNewCC(String capitalname, String countryname){
    City newcapital = new City(capitalname );
    NATS newcountry = new NATS();
    newcountry.setNationName(countryname);
    newcountry.setCapital(newcapital);
    em.persist(newcountry); // both objects persisted well, with "capId" still null
    return newcountry;
  }

  public void updateCapitalId(Nations country){
    country.setCapitalId(country.getCapital().getcityId());
    em.merge(country);
  }
}

服务内容如下:

通用资源。Java语言

@Path("generic")
public class GenericResource {

@Context
private UriInfo context;
@EJB
private somebean r;

@GET
@Path("/inscountry")
@Produces("application/json")
public List<NATS> insCountry( @QueryParam("countryname") String countryname, @QueryParam("capitalname") String capitalname){      
    NATS newcountry = r.insertNewCC(capitalname, countryname);
    //r.updateCapitalId(newcountry);   <-- i want to avoid using this line
    List<NATS> result= r.getListNATS();
    return result;
}

当我评论这行时:r.updateCapitalId(newcountry); 我得到了一对国家和首都,其关系在JSON中正确显示,但在会话结束时。由于外键未保存,因此会丢失关系。持久化完成后,NATs实体中的capId为空。所以我需要一个坚持&1合并以完成此操作。除了使用我评论的那句话,还有更好的解决方案吗? 非常感谢。

2 回复 | 直到 7 年前

Tejas 7 年前

重新设计实体NAT,如下所示:

package com;

import java.io.Serializable;

import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.OneToOne;
import javax.persistence.Table;

@Entity
@Table(name = "NATS")

public class NATS
    implements Serializable
{
    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Integer code;
    private String name;
    // for foreign key purpose
    @OneToOne(cascade = CascadeType.PERSIST)
    @JoinColumn(name = "cap_id")
    private City capital;

    public City getCapital()
    {
        return this.capital;
    }

    public void setCapital(City newcapital)
    {
        this.capital = newcapital;
    }

    public Integer getCode()
    {
        return this.code;
    }

    public void setCode(Integer code)
    {
        this.code = code;
    }

    public String getName()
    {
        return this.name;
    }

    public void setName(String name)
    {
        this.name = name;
    }
}

然后执行代码将保持不变:

    City newcapital = new City(capitalname);
    NATS newcountry = new NATS();
    newcountry.setName(countryname);
    newcountry.setCapital(newcapital);
    this.entityManager.persist(newcountry);

dmarquina 7 年前

首先,试着使用缩进和格式化程序,因为你的代码一团糟。其次,您希望保存两个实体(NAT和Country),因此必须取消注释更新城市或逐个保留的行。如果您正在启动一个新的应用程序,我建议您使用Spring boot和它的SpringRepository界面,以使这些事情变得更简单和清晰。