jpql - JPQL 查询 - 从父项获取列表中的子项

Question

当我有文件夹：id和记录：refId（命名参数）时，如果文件夹中存在记录，我将如何创建 JPQL 查询来获取记录。我希望从查询中返回记录，因为需要记录的其他数据。

以下是实体：

@Entity
public class Folder {
    @Id
    @Column(name = "id")
    private Long id;

    @OneToMany(targetEntity = Record.class, cascade = { CascadeType.ALL })
    @JoinColumn(name = "RECORD_FOLDER_0")
    @OrderBy("id ASC")
    private List<Record> records;
    ...
}

@Entity
public class Record {
    @Id
    @Column(name = "id")
    private Long id;

    @Basic
    @Column(name = "refId")
    private Long refId;

    @Basic
    @Column(name = "data", length = 255)
    private String data;
    ...
}

常规 SQL 看起来像：

.createNativeQuery(String.format("SELECT * FROM record r WHERE r.refId=%d AND r.RECORD_FOLDER_0=%d", refId, folderId));

我正在努力研究如何使用 JPQL 查询来做到这一点。

Answer 1

Since you don't have a reference to the parent Folder from Record, you'll have to start with the Folder and join the child Records. Something like this should do the trick:

TypedQuery<Record> q = em.createQuery(
    "SELECT r FROM Folder f JOIN f.records r " +
    "WHERE f.id = :folderId AND r.refId = :refId", Record.class);
q.setParameter("folderId", folderId);
q.setParameter("refId", refId);