[hibernate-issues] [Hibernate-JIRA] Created: (HHH-2351) PersistentMap incorrectly flags rows for insertion when data contains NULLs

[Matt Doran (JIRA)]

PersistentMap incorrectly flags rows for insertion when data contains NULLs
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         Key: HHH-2351
         URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-2351
     Project: Hibernate3
        Type: Bug

  Components: core  
    Versions: 3.0.5, 3.2.1    
 Environment: Found in 3.0.5, but the code in 3.2.1 contains the same error.
    Reporter: Matt Doran
 Attachments: partial-map-null-fix.patch

There is a bug in the org.hibernate.collection.PersistentMap implementation that can cause hibernate to try to insert duplicate rows when the map values from the database contain null.

The issue is caused when incorrectly testing if an row exists in a Map.  The persistent map testing whether map values are == null instead of checking to see if the key exists.  i.e. using Map.get(key) == null instead of Map.containsKey(key).
This is incorrect, because the map values are allowed to contain null.

This problem can bee seen in the following code:

	public boolean needsInserting(Object entry, int i, Type elemType) 
	throws HibernateException {
		final Map sn = (Map) getSnapshot();
		Map.Entry e = (Map.Entry) entry;
		return e.getValue()!=null && sn.get( e.getKey() )==null;
	}

If the map contains an entry: key1 -> NULL , and we try to update the value , then the above code will incorrectly result in a new row being attempted to be inserted (instead of updated).

Instead of checking whether the values == null the Map.containKey() method should be used.

I think similar bugs also exist in the "needsUpdating" and "getDeletes" methods.  I've attached a possible patch for the "needsInserting" and "needsUpdating" methods, but I don't understand everything that's going on here or the code in "getDeletes" ....  but I'm sure you guys will know the right answer!


SIDE NOTE:
The reason this has just started causing us an issue in our product (PaperCut NG), is that we are porting to Oracle, which turns empty strings into NULLs (which is annoying).  For other databases we stored blank strings in the values, but in Oracle they become NULLs (whether we like it or not).  We then start getting errors about violating uniqueness constraints when Hibernate incorrectly these attempts to re-insert the rows in the database.

This is of critical importance to us.  In the short-term, our work-around might involve just deleting rows that contain NULL.


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