如何在 JPA /Eclipselink 2.6.5 中使用三个级别的“LEFT JOIN”获取 Table3(关系 OneToOne)?
此命令不获取它:(错误)
SELECT t1 FROM Table1 t1 LEFT JOIN FETCH t1.table2 t2
LEFT JOIN FETCH t2.table3
此命令获取它,但不要先保留“LEFT”:(错误)
SELECT t1 FROM Table1 t1 LEFT JOIN FETCH t1.table2
LEFT JOIN FETCH t1.table2.table3
此获取它,但它只有两个级别:(不需要)
SELECT t2 FROM Table2 t2 LEFT JOIN FETCH t2.table3
表格1:
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Basic(optional = false)
@Column(name = "Id")
private Integer id;
@JoinColumn(name = "Table2", referencedColumnName = "Id")
@ManyToOne(fetch = FetchType.LAZY)
private Table2 table2;
表二:
@Id
@Basic(optional = false)
@NotNull
@Column(name = "Id")
private Integer id;
@OneToMany(cascade = CascadeType.ALL, mappedBy = "table2")
private Collection<Table1> table1Collection;
@OneToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL, mappedBy = "table2")
private Table3 table3;
表3:
@Id
@Basic(optional = false)
@NotNull
@Column(name = "Id")
private Integer id;
@JoinColumn(name = "Table2", referencedColumnName = "Id", insertable = false, updatable = false)
@OneToOne(fetch = FetchType.LAZY, optional = false)
private Table2 table2;
谢谢!
JPA/JPQL 不支持嵌套的获取连接。要解决此问题,您可以向查询添加查询提示,以告诉它您想要使用左外连接连接什么。fetch -join查询提示有一个更好的例子来展示它是如何使用的。
Query query = em.createQuery("SELECT t1 FROM Table1 t1", Table1.class);
query.setHint("eclipselink.LEFT_FETCH", "t1.table2");
query.setHint("eclipselink.LEFT_FETCH", "t1.table2.table3");
我认为您需要在 table1 和 table2 之间进行右连接,因此请改用“RIGHT JOIN”重试前两个示例。
您的各种尝试生成的 SQL 是什么?EclipseLink 2.4+ 应该支持 JPQL stackoverflow.com/a/16693590/496099中的嵌套连接提取