java - 查询仅在子实体不为空时返回实体

Question

我有以下查询:

  @Query("SELECT new de.hiqs.project.Project(project.id, project.name, project.isArchived, " +
          "project.customer.id, project.customer.name, project.customer.smallestTimeUnitEnabled, " +
          "project.customer.smallestTimeUnit, project.defaultDailyEntrySettings.id, " +
          "project.defaultDailyEntrySettings.performanceRecord, project.defaultDailyEntrySettings.startDateHour," +
          "project.defaultDailyEntrySettings.startDateMinute, project.defaultDailyEntrySettings.endDateHour, " +
          "project.defaultDailyEntrySettings.endDateMinute, project.defaultDailyEntrySettings.pause ) " +
          "FROM Project project")
  List<Project> findAllInOneRequest();

所以我有一个查询，它返回具有所选属性的所有项目，以便在一个请求中获取所有内容并避免 N+1 问题。如您所见，Project 与 DefaultDailyEntrySettings 存在关系(外键)。问题是并非每个项目都有 DefaultDailyEntrySettings 子项(数据库中为 null)。因此查询仅返回有一个的projects。我希望它返回所有 projects 并在 defaultDailyEntrySettings 不存在时将其初始化为 null，而不是在没有 defaultdailyEntrySettings 的情况下不返回 projects 。有办法做到吗？

另一种选择是自动为每个project提供一个带有空字段的defaultDailyEntrySettings，而不是外键为空，但我不知道如何使用注释来做到这一点。

Answer 1

也许是这样的？

@Query("SELECT new de.hiqs.project.Project(project.id, project.name, project.isArchived, " +
      "project.customer.id, project.customer.name, project.customer.smallestTimeUnitEnabled, " +
      "project.customer.smallestTimeUnit, project.defaultDailyEntrySettings.id, " +
      "project.defaultDailyEntrySettings.performanceRecord, project.defaultDailyEntrySettings.startDateHour," +
      "project.defaultDailyEntrySettings.startDateMinute, project.defaultDailyEntrySettings.endDateHour, " +
      "project.defaultDailyEntrySettings.endDateMinute, project.defaultDailyEntrySettings.pause ) " +
      "FROM Project project " +
      "WHERE EXISTS (SELECT 1 FROM project.defaultDailyEntrySettings)" +
      "UNION ALL " + 
      "SELECT new de.hiqs.project.Project(project.id, project.name, project.isArchived, " +
      "project.customer.id, project.customer.name, project.customer.smallestTimeUnitEnabled, " +
      "project.customer.smallestTimeUnit, null, " +
      "null, null," +
      "null, null, " +
      "null, null ) " +
      "FROM Project project " +
      "WHERE NOT EXISTS (SELECT 1 FROM project.defaultDailyEntrySettings)")
List<Project> findAllInOneRequest();