一尘不染

有人可以在hibernate状态下解释mappedBy吗?

java

需要使用一对多和多对一关系。这是我对象中的双向关系,因此我可以从任一方向来回移动。mappedBy是推荐的解决方法,但是,我听不懂。有人可以解释:

推荐的使用方式是什么?
它解决什么目的?
就我的示例而言,这是带有注释的类:

  • Airline 拥有许多 AirlineFlights
  • 许多 AirlineFlights属于一个 Airline

航空公司:

@Entity 
@Table(name="Airline")
public class Airline {
    private Integer idAirline;
    private String name;

    private String code;

    private String aliasName;
    private Set<AirlineFlight> airlineFlights = new HashSet<AirlineFlight>(0);

    public Airline(){}

    public Airline(String name, String code, String aliasName, Set<AirlineFlight> flights) {
        setName(name);
        setCode(code);
        setAliasName(aliasName);
        setAirlineFlights(flights);
    }

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Column(name="IDAIRLINE", nullable=false)
    public Integer getIdAirline() {
        return idAirline;
    }

    private void setIdAirline(Integer idAirline) {
        this.idAirline = idAirline;
    }

    @Column(name="NAME", nullable=false)
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = DAOUtil.convertToDBString(name);
    }

    @Column(name="CODE", nullable=false, length=3)
    public String getCode() {
        return code;
    }
    public void setCode(String code) {
        this.code = DAOUtil.convertToDBString(code);
    }

    @Column(name="ALIAS", nullable=true)
    public String getAliasName() {
        return aliasName;
    }
    public void setAliasName(String aliasName) {
        if(aliasName != null)
            this.aliasName = DAOUtil.convertToDBString(aliasName);
    }

    @OneToMany(fetch=FetchType.LAZY, cascade = {CascadeType.ALL})
    @JoinColumn(name="IDAIRLINE")
    public Set<AirlineFlight> getAirlineFlights() {
        return airlineFlights;
    }

    public void setAirlineFlights(Set<AirlineFlight> flights) {
        this.airlineFlights = flights;
    }
}

航空公司航班:

@Entity
@Table(name="AirlineFlight")
public class AirlineFlight {
    private Integer idAirlineFlight;
    private Airline airline;
    private String flightNumber;

    public AirlineFlight(){}

    public AirlineFlight(Airline airline, String flightNumber) {
        setAirline(airline);
        setFlightNumber(flightNumber);
    }

    @Id
    @GeneratedValue(generator="identity")
    @GenericGenerator(name="identity", strategy="identity")
    @Column(name="IDAIRLINEFLIGHT", nullable=false)
    public Integer getIdAirlineFlight() {
        return idAirlineFlight;
    }
    private void setIdAirlineFlight(Integer idAirlineFlight) {
        this.idAirlineFlight = idAirlineFlight;
    }

    @ManyToOne(fetch=FetchType.LAZY)
    @JoinColumn(name="IDAIRLINE", nullable=false)
    public Airline getAirline() {
        return airline;
    }
    public void setAirline(Airline airline) {
        this.airline = airline;
    }

    @Column(name="FLIGHTNUMBER", nullable=false)
    public String getFlightNumber() {
        return flightNumber;
    }
    public void setFlightNumber(String flightNumber) {
        this.flightNumber = DAOUtil.convertToDBString(flightNumber);
    }
}

编辑:

数据库模式:

AirlineFlights具有idAirline作为ForeignKey,而Airline没有idAirlineFlights。这使得AirlineFlights作为所有者/识别实体?

从理论上讲,我希望航空公司成为airlightFlights的所有者。


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2020-03-11

共1个答案

一尘不染

通过@JoinColumn在两个模型上都指定,你就没有双向关系。你有两个单向关系,并且在那个位置有一个非常混乱的映射。你要告诉这两个模型“拥有” IDAIRLINE列。实际上,实际上其中只有一个!“正常”的事情是完全@JoinColumn脱颖而出@OneToMany,而是将maptedBy添加到@OneToMany

@OneToMany(cascade = CascadeType.ALL, mappedBy="airline")
public Set<AirlineFlight> getAirlineFlights() {
    return airlineFlights;
}

这告诉Hibernate:“在我有一个用来查找配置的集合上,检查名为’airline’的bean属性。”

2020-03-11