Java 持久性查询语言 JOIN

Question

我有两张桌子：

A(bigint id, ...)
B(bigint id, varchar name, bigint id_A)

现在我想从 A 中获取存在于 B 中的所有行（并且 B 中的那些行具有名称，例如 Andy）

请帮我创建动态查询

A类

@Entity
@Table(name = "A", schema = "mySchema")
@Cache(usage = CacheConcurrencyStrategy.TRANSACTIONAL)
public class A{

    @Id
    private Long id;

}

B类

@Entity
@Table(name = "B",
    schema = "mySchema",
    uniqueConstraints = { @UniqueConstraint(columnNames = {
    "some_id", "id_A" }) })
public class B{

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO, generator = "Seq")
    @SequenceGenerator(name = "Seq", sequenceName = "mySchema.mySeq")
    private Long id;

    @OneToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "id_A", nullable = false)
    private A a;

    @Column(name = "id_A", updatable = false, insertable = false)
    private Long IdA;
}

Answer 1

有几个奇怪的部分。例如这个：

@OneToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "id_A", nullable = false)
private A a;

@Column(name = "id_A", updatable = false, insertable = false)
private Long IdA;

使用@JoinColumn 注释，您告诉JPA 提供程序它应该使用指定的列进行内部映射，但是使用IdA 字段，您正在尝试自己管理该列。会是哪一个？