JPA JOIN查詢問題

Question

我正在嘗試JPA查詢，但以下查詢始終出現錯誤

SELECT p
FROM usertype_permissions up
JOIN permissions p ON up.PERMISSION_ID = p.ID
WHERE up.USERTYPE_ID = 1

錯誤：

Caused by: java.lang.IllegalArgumentException: An exception occurred while
creating a query in EntityManager: 

Exception Description: Syntax error parsing the query
[SELECT p
FROM usertype_permissions up
JOIN permissions p ON up.PERMISSION_ID = p.ID
WHERE up.USERTYPE_ID = 1].

Answer 1

在JPQL中，您必須使用實體名稱（默認情況下是Java類的名稱），對我來說usertype_permissions是實體名稱/ Java類看起來很奇怪。

看起來您正在使用表名，並且連接后的單詞必須引用類的屬性，例如l.books

例：

@Entity
public class Lib implements Serializable {
      @OneToMany
      private Set<Book> books;
}

@Entity
public class Book implements Serializable {
      @OneToOne
      private Lib lib;
}

JPQL查詢如下所示：

SELECT l FROM Lib JOIN l.books books