限制JPA规范查询以获取所需数据

Question

我有3张桌子：

School
    school_id, school_name, student_id
Student
    student_id, student_name ,subject_id
Subject
    subject_id, subject_name

学校之间存在一对多的关系-

我正在编写规范查询以获取特定学校的学生：

List<Student> students = schoolRepo.findAll(Specification.where (findStudents(schoolId));

public static Specification<Student> findStudents(long schoolId) {
    return (root, query, cbuilder) -> {
        root.fetch("students", JoinType.LEFT);
        return cbuilder.and(cbuilder.equal(root.get("school"), schoolId));
    };
}

虽然我没有在规范查询或代码中的任何地方获取主题（如使用get）。

我仍然可以在生成的查询中的日志中看到主题最终被获取。

我如何更新我的查询以仅限于学校

请建议。

Answer 1

您可以尝试改用EntityGraph。它有助于提高加载实体的性能。你可以这样做

@Entity
@NamedEntityGraph (
  name="school-students",
  attributeNodes = {
     @NamedAttributeNode("students")
  }
)
public class School implements Serializable { ... }


And then in your repository use it like this : 

@Override
@EntityGraph(value = "school-students",
     type = EntityGraph.EntityGraphType.FETCH)
@Query( value = "SELECT s FROM School s where s.id =:id")
School findOne();