HQL recursion, how do I do this?

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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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