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Date: Fri, 2 May 2008 16:31:23 -0700 (PDT)
From: Fay Wang <fyw300@yahoo.com>
Reply-To: fyw300@yahoo.com
Subject: Unpredictable set clause in generated sql
To: dev@openjpa.apache.org
Cc: Fay Wang <fyw300@yahoo.com>
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Message-ID: <955848.90434.qm@web55806.mail.re3.yahoo.com>

Hi,
      Our application requires the push-down sql from named/dynamic query be the same each time a same JPQL is executed. In the following JPQL example,
	
      query="UPDATE BasicA t set t.name= ?1, t.age = ?2 WHERE t.id = ?3"

      we observe two different push-down sql could be generated:
      
      UPDATE PDQBasicA t0 SET name = ?, age = ? WHERE (t0.id = ?)

      UPDATE PDQBasicA t0 SET age = ?, name = ? WHERE (t0.id = ?)

      This unpredictable behavior breaks our application. The indeterministic ordering of the update list is due to the indeterministic ordering provided by HashMap and HashSet in QueryExpressions and JPQLExpressionBuilder, respectively.

      When the HashMap is changed to LinkedHashMap and HashSet to LinkedHashSet, the access order based on insertion will be preserved and the generated push-down sql will have predictable ordering of update list. Is there an alternative way to address this issue?

      Should a JIRA issue be open to fix this problem? Any comment is appreciated.

	In QueryExpressions:
    /**
     * Add an update.
     */
    public void putUpdate(Path path, Value val) {
        if (updates == Collections.EMPTY_MAP)
            updates = new HashMap();  <== change HashMap to LinkedHashMap
        updates.put(path, val);
    }

In JPQLExpressionBuilder:

    JPQLNode[] findChildrenByID(int id) {
        Collection set = new HashSet(); <== change HashSet to LinkedHashSet
        findChildrenByID(id, set);
        return (JPQLNode[]) set.toArray(new JPQLNode[set.size()]);
    }

-Fay


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