java - 查询仅返回其子级不为null的实体

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();

因此，我有一个查询，该查询返回具有选定属性的所有项目，以在一个请求中获得所有内容并避免N + 1问题。如您所见，Project与DefaultDailyEntrySettings有一个关系（外键）。问题在于，并非每个项目都有一个DefaultDailyEntrySettings子级（数据库中为null）。因此查询仅返回具有1的projects。我希望它返回所有projects，如果不存在，只需用空值初始化defaultDailyEntrySettings即可，而不是在没有projects的情况下不返回defaultdailyEntrySettings。有办法吗？

另一个选择是为每个project自动提供一个具有空字段的defaultDailyEntrySettings而不是外键为null，但是我无法弄清楚如何使用注释。

最佳答案

也许是这样吗？

@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();