從深層遞歸父子關係構建JSON

Question

我在postgres數據庫中有以下記錄。 parent_pk與父子關係中的pk相關。 pk = 1是所有孩子的直接和間接的父母。

pk    name    type   parent_pk 
---   ----    ----   --------- 
1    hnumber101  house   1 
2    hnumber201  house   1 
791   dodge_charger vehicle   1 
801   mustang   vehicle   791 
595020   civic   vehicle   2 
10077661099 john    user   10046725614 
10046725614 mesto   dev    1 
801   shen    house   791 
44444444  crep    house   10046725614 
22222222  keper   user   10046725614 
11111111  show    house   10046725614 
84257651  shen    house   801 
11    lemp    house   2 

我想生成以下格式 -

{ 
    "children" : [ 
    { "pk" : "1", "name" : "hnumber101", "children" : [ 
     { "pk" : "10046725614", "name" : "mesto", "children" : [ 
      { "pk" : "10077661099", "name" : "john", "children" : [] }, 
      { "pk" : "44444444", "name" : "crep", "children" : [] }, 
      { "pk" : "22222222", "name" : "keper", "children" : [] }, 
      { "pk" : "11111111", "name" : "show", "children" : [] } 
     ] } 
     ] }, 
     { "pk" : "791", "name" : "dodge_charger", "children" : [ 
     { "pk" : "801", "name" : "mustang", "children" : [ 
      { "pk" : "84257651", "name" : "shen", "children" : [ 
      ] } 
     ] }, 
     { "pk" : "2", "name" : "hnumber201", "children" : [ 
      { "pk" : "595020", "name" : "civic", "children" : [] }, 
      { "pk" : "11", "name" : "lemp", "children" : [] } 
     ] } 
     ] } 
    ] } 
    ] 
} 

一個JSON出上述與我目前的代碼，我可以能夠得到的只有PK = 1的孩子的孩子。 但深層遞歸沒有發生。

Collection<GatherEntity> gatherEntityChildren= gatherManager.findByParentGatherId(1); 
getRecursiveGatherFromParent(gatherEntityChildren, gatherListParent); 

private List<Gather> getRecursiveGatherFromParent(Collection<GatherEntity> gatherEntityChildren, List<Gather> gatherListParent) throws JSONException {  


     if(gatherEntityChildren != null && gatherEntityChildren.size() > 0) { 
      for (Iterator<gatherEntity> iterator = gatherEntityChildren.iterator(); iterator.hasNext();) { 
       GatherEntity gatherEntity = (GatherEntity) iterator.next(); 

       Gather gather = getGatherFromEntity(gatherEntity); 
       List<Gather> gatherChildren = populateGatherAndChild(gatherEntity); 
       gather.setChildren(new HashSet<Gather>(gatherChildren)); 
       gatherListParent.add(gather); 
      } 
     } 
     return gatherListParent; 
    } 

    private List<Gather> populateGatherAndChild(GatherEntity gatherEntity) { 
     Collection<GatherEntity> gatherEntityChildren= gatherManager.findByParentGatherId(gatherEntity.getGatherId()); 
     List<Gather> gatherList = gatherEntityChildren.stream().map(UserAPIImpl::getGatherFromEntity).collect(Collectors.toList());  
     return gatherList; 
    } 

    private static Gather getGatherFromEntity(GatherEntity gatherEntity) { 
     Gather gather = new Gather(); 
     gather.setGatherId(gatherEntity.getGatherId()); 
     gather.setName(gatherEntity.getName()); 
     return gather; 
    } 

Answer 1

你已經錯過了對孩子的遞歸調用：

 if(gatherEntityChildren != null && gatherEntityChildren.size() > 0) { 
     for (Iterator<gatherEntity> iterator = gatherEntityChildren.iterator(); iterator.hasNext();) { 
      GatherEntity gatherEntity = (GatherEntity) iterator.next(); 

      Gather gather = getGatherFromEntity(gatherEntity); 
      Collection<GatherEntity> gatherChildren = populateGatherAndChild(gatherEntity); 

      List<Gather> gatherList = gatherEntityChildren.stream().map(UserAPIImpl::getGatherFromEntity).collect(Collectors.toList()); 
      gather.setChildren(new HashSet<Gather>(gatherList)); 
      gatherListParent.add(gather); 

      getRecursiveGatherFromParent(gatherChildren, gatherListParent); 
     } 
    } 
    return gatherListParent; 
} 

private List<GatherEntity> populateGatherAndChild(GatherEntity gatherEntity) { 
    return gatherManager.findByParentGatherId(gatherEntity.getGatherId()); 
}