java - 多对多、Hibernate 问题、AssociationOverrides

Question

我在理解 hibernate 的多对多部分时遇到问题:(。

我正在尝试创建一些表，但我不知道如何在它们之间创建有效的关系。

我有表 UserCurs 和 OrarCurs，然后我有中间表 Prezenta。

这是我的结构。

用户CursID

import javax.persistence.Embeddable;

import javax.persistence.ManyToOne;

@Embeddable
public class UserCursID implements java.io.Serializable {

    private static final long serialVersionUID = -9120607274421816301L;


    private User user;
    private Curs cs;


    @ManyToOne
    public User getUser() {
        return user;
    }
    public void setUser(User user) {
        this.user = user;
    }
    @ManyToOne
    public Curs getCs() {
        return cs;
    }
    public void setCs(Curs cs) {
        this.cs = cs;
    }
}

UserCurs(也是 User 和 Curs 的中间表):

@Entity
@Table(name="user_curs")
@AssociationOverrides({
    @AssociationOverride(name="pk.user", joinColumns = @JoinColumn(name="id_user")),
    @AssociationOverride(name="pk.cs", joinColumns = @JoinColumn(name="id_curs"))
})
public class UserCurs implements java.io.Serializable {

    private static final long serialVersionUID = 4050660680047579957L;

    private UserCursID pk = new UserCursID();

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    private Integer uc_id;

    public Integer getUc_id() {
        return uc_id;
    }

    public void setUc_id(Integer uc_id) {
        this.uc_id = uc_id;
    }

    @EmbeddedId
    public UserCursID getPk() {
        return pk;
    }
    public void setPk(UserCursID pk) {
        this.pk = pk;
    }
}

奥拉尔库斯:

@Entity
@Table(name="OrarCurs")
public class OrarCurs {
    @Id
    @Column(name="oc_id")
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    private Integer oc_id;

    @ManyToOne(fetch = FetchType.LAZY, cascade = {CascadeType.DETACH, CascadeType.MERGE, CascadeType.REFRESH, CascadeType.PERSIST})
    @JoinColumn(name="curs_id")
    private Curs orarcurs;

    @Column(name="data_curs")
    private Date dataCurs;

    public Integer getOc_id() {
        return oc_id;
    }

    public void setOc_id(Integer oc_id) {
        this.oc_id = oc_id;
    }

    public Curs getOrarcurs() {
        return orarcurs;
    }

    public void setOrarcurs(Curs orarcurs) {
        this.orarcurs = orarcurs;
    }

    public Date getDataCurs() {
        return dataCurs;
    }

    public void setDataCurs(Date dataCurs) {
        this.dataCurs = dataCurs;
    }
}

和 PrezentaID:

import javax.persistence.Embeddable;
import javax.persistence.ManyToOne;

@Embeddable
public class PrezentaID implements java.io.Serializable{

    private static final long serialVersionUID = -9120607274421816301L;

    private UserCurs usercurs;
    private OrarCurs orar;

    @ManyToOne
    public UserCurs getUserCurs() {
        return usercurs;
    }
    public void setUserCurs(UserCurs usercurs) {
        this.usercurs = usercurs;
    }

    @ManyToOne
    public OrarCurs getOrar() {
        return orar;
    }
    public void setOrar(OrarCurs orar) {
        this.orar = orar;
    }
}

Prezenta 类:

@Entity
@Table(name="prezenta")
@AssociationOverrides({
    @AssociationOverride(name="pk1.usercurs", joinColumns = @JoinColumn(name="id_usercurs", referencedColumnName="usercurs_id")),
    @AssociationOverride(name="pk1.orar", joinColumns = @JoinColumn(name="id_orar", referencedColumnName="oc_id"))
})
public class Prezenta implements java.io.Serializable{

    private static final long serialVersionUID = 4050660680047579957L;

    private PrezentaID pk1 = new PrezentaID();
    private Boolean Present;

    @EmbeddedId
    public PrezentaID getPk1() {
        return pk1;
    }

    public Boolean getPresent() {
        return Present;
    }

    public void setPresent(Boolean present) {
        Present = present;
    }

    public void setPk1(PrezentaID pk1) {
        this.pk1 = pk1;
    }

}

运行 main.class 后，一切正常，所有表都已创建，但在我的 Prezenta 表中添加了这三列

Hibernate:更改表 prezenta 添加约束 FK_8ndmk871bbblvtt50y0qhrvl7 外键 (id_orar) 引用 OrarCurs (oc_id)

Hibernate:alter table prezenta添加约束FK_8vv4yxxpxc85vew0ox779r2kn外键(userCurs_id_curs，userCurs_id_user)引用user_curs(id_curs，id_user)

基本上，该表具有以下列:id_orar、userCurs_id_curs、userCurs_id_user，但我不想要最后两列，我想要而不是与 uc_id 对应的一列(来自 UserCurs)，我不知道如何执行此操作。

Answer 1

您不必为此映射创建 Prezenta 类。您所需要的只是要映射的两个类和注释@ManyToMany。这是一个好话题: https://www.baeldung.com/hibernate-many-to-many Hibernate 将使用您的类中的 pk 创建连接表

@Entity
@Table(name="db table1 name")
Class1{
    @Id
    @Column(name="id in table 1")
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    private Integer class1_id;

    @JoinTable(
        name = "class1_class2", 
        joinColumns = { @JoinColumn(name = "class1_id") }, 
        inverseJoinColumns = { @JoinColumn(name = "class2_id") }
    )
    private List<Class2> list1;
}

@Entity
@Table(name="db table2 name")
Class2{
    @Id
    @Column(name="id in table 1")
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    private Integer class1_id;

 @ManyToMany(mappedBy = "list1")
 private List<Class1> list2
}