Question

每个主题，我有一个实体A，比如说a1（PK），a2。实体B，列a2（PK），b1 实体C，列b1（PK），c1

所以用a2连接到B，然后用b1连接到C. （它们都是一对一的关系）

这些实体在web服务中使用，当被调用时将生成包含这些实体列表的XML文件。现在生成一个XML，将实体A和B与字段a1，a2，a1组合在一起非常简单。

但是，如果我想生成仅显示实体A和实体C的XML，那么需要什么语法/注释？我的意思是，我如何设置该实体A以便它可以实现？

如果我可以从实体A，B，C获得所有字段，我也会解决。

我正在使用jpa2，ejb3.1

修改：添加示例。

实体A

@Entity
@Table(name = "TABLE_A")
@XmlRootElement
@NamedQueries({
    @NamedQuery(name = "MyComplex.findAll", query = "SELECT j FROM MyComplex j"),
    @NamedQuery(name = "MyComplex.findA1", query = "SELECT j FROM MyComplex j WHERE j.a1 = :A1")
})
public class MyComplex implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id
    @Column(name = "A1", length = 1)
    private String a1;

    @Column(name = "A2", length = 1)
    private String a2;

    public MyComplex() {
    }

    public MyComplex(String a1) {
        this.a1 = a1;
    }

    public String getA1() {
        return a1;
    }

    public void setA1(String a1) {
        this.a1 = a1;
    }

    public String getA2() {
        return a2;
    }

    public void setA2(String a2) {
        this.a2 = a2;
    }

    @Override
    public int hashCode() {
        int hash = 0;
        hash += (a1 != null ? a1.hashCode() : 0);
        return hash;
    }

    @Override
    public boolean equals(Object object) {
        if (!(object instanceof MyComplex)) {
            return false;
        }
        MyComplex other = (MyComplex) object;
        if ((this.a1 == null && other.a1 != null) || (this.a1 != null && !this.a1.equals(other.a1))) {
            return false;
        }
        return true;
    }    
    @Override
    public String toString() {
        return "jpa.mypackage.Table_A[a1=" + a1 + " ]";
    }      
}

实体B

@Entity
@Table(name = "TABLE_B")
@XmlRootElement
@NamedQueries({
    @NamedQuery(name = "Table_B.findAll", query = "SELECT j FROM Table_B j"),
    @NamedQuery(name = "Table_B.findA2", query = "SELECT j FROM Table_B j WHERE j.a2 = :A2")
})
public class Table_B implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id
    @Column(name = "A2", length = 1)
    private String a2;

    @Size(max = 1)
    @Column(name = "B1", length = 1)
    private String b1;

    //entity constructor here

    //entity get/set methods here

    //entity hash methods here      
}

实体C

@Entity
@Table(name = "TABLE_C")
@XmlRootElement
@NamedQueries({
    @NamedQuery(name = "Table_C.findAll", query = "SELECT j FROM Table_C j"),
    @NamedQuery(name = "Table_C.findB1", query = "SELECT j FROM Table_C j WHERE j.b1 = :B1")
})
public class Table_C implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id
    @Column(name = "B1", length = 1)
    private String b1;

    @Size(max = 1)
    @Column(name = "C1", length = 1)
    private String c1;

    //entity constructor here

    //entity get/set methods here

    //entity hash methods here      
}

修改实体A以加入实体B

@Entity
@Table(name = "TABLE_A")
@XmlRootElement
@NamedQueries({
    @NamedQuery(name = "MyComplex.findAll", query = "SELECT j FROM MyComplex j"),
    @NamedQuery(name = "MyComplex.findA1", query = "SELECT j FROM MyComplex j WHERE j.a1 = :A1")
})
public class MyComplex implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id
    @Column(name = "A1", length = 1)
    private String a1;

    @Column(name = "A2", length = 1)
    private String a2;

    @OneToOne(cascade = CascadeType.ALL, fetch = FetchType.EAGER)
    @JoinColumn(name="A2", referencedColumnName="A2")
    private Table_B table_B;

    //entity constructor here

    //entity get/set methods here
    public Table_B getTable_B() {
        return table_B;
    }

    public void setTable_B(Table_B table_B) {
        this.table_B = table_B;
    }    

    //entity hash methods here  
}

Answer 1

根据你的图，我看到Table_B只是A和C的连接表。如果在MyComplex.java中使用JoinTable设置OneToOne注释，那么我相信你可以设置Table_A和Table_C的关系。

@Entity
@Table(name = "TABLE_A")
@XmlRootElement
@NamedQueries({
    @NamedQuery(name = "MyComplex.findAll", query = "SELECT j FROM MyComplex j"),
    @NamedQuery(name = "MyComplex.findA1", query = "SELECT j FROM MyComplex j WHERE j.a1 = :A1")
})
public class MyComplex implements Serializable {
/* ------------------------------------ */
@OneToOne
@JoinTable(
        name="Table_B",
        joinColumns=
            @JoinColumn(name="A2", referencedColumnName="A2"),
        inverseJoinColumns=
            @JoinColumn(name="B1", referencedColumnName="B1")
    )
private Table_C tableC;
/* ------------ */
}

JPA2如何显示表A中的字段，表C如果表A连接表B然后连接表C？

1 个答案: