HQL递归，我该怎么做？ [英] HQL recursion, how do I do this?

问题描述

我有一个树结构，其中每个 Node 有一个父元素，一个 Set< Node>孩子。每个节点都有一个字符串标题，我想在其中选择 Set< String>标题，是该节点和所有父节点的标题。我如何编写这个查询？

单个标题的查询就是这样，但就像我说的，我希望它扩展到整个家长分支。 / p>

  SELECT node.title FROM节点WHERE node.id =：id 
  

干杯

Nik

解决方案

你不能用HQL进行递归查询。 查看此。如前所述，它甚至没有标准的SQL。您有两种选择：

• 编写供应商特定递归本机 SQL查询



• make多个查询。例如：
  
  

    //使用查询获取第一个节点
   while（currentNode.parent！= null）{ 
   Query q = //创建查询
   q.setParameter（id，currentNode.getParentId（））; 
   Node currentNode =（Node）q.getSingleResult（）; 
   nodes.add（currentNode）; //这是Set 
  } 
    

<我肯定会选择第二种方式。

I have a tree structure where each Node has a parent and a Set<Node> children. Each Node has a String title, and I want to make a query where I select Set<String> titles, being the title of this node and of all parent nodes. How do I write this query?

The query for a single title is this, but like I said, I'd like it expanded for the entire branch of parents.

SELECT node.title FROM Node node WHERE node.id = :id

Cheers

Nik

解决方案

You can't do recursive queries with HQL. See this. And as stated there it is not even standard SQL. You have two options:

• write a vendor-specific recursive native SQL query

• make multiple queries. For example:

  // obtain the first node using your query
  while (currentNode.parent != null) {
     Query q = //create the query
     q.setParameter("id", currentNode.getParentId());
     Node currentNode = (Node) q.getSingleResult();
     nodes.add(currentNode); // this is the Set
  }
  

I'd definitely go for the 2nd option.

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