CacheModel does not support caching null results
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Key: IBATIS-174
URL: http://issues.apache.org/jira/browse/IBATIS-174
Project: iBatis for Java
Type: Bug
Components: SQL Maps
Versions: 2.0.9
Environment: All
Reporter: Chris Mathews
Attachments: CacheModelTest.java
Currently IBatis caching does not support caching null results. Any null
object placed into the CacheModel will always result in what is interpertated
as a cache miss when it is looked up again. When a null object put into the
cache (by calling CacheModel.putObject()) it is actually entered into the cache
as a CacheModel.NULL_OBJECT (which is fine). However, when the same object is
retrieved (by calling CacheModel.getObject()) the CacheModel.NULL_OBJECT is
translated into an actual Java null value. A null value being returned by
CacheModel.getObject() is considered a cache miss in the calling code
(CachingStatement.executeQueryForList() and
CachingStatement.executeQueryForObject())... this is causing a hard hit to
database unnecessarily.
We are running into this problem while trying to cache a simple holiday table
in one of our applications. The query takes a date a parameter and returns a
row if the holiday exists or null if it does not. Since the vast majority of
days are not holidays and therefore return null, 95% of these statements are
actually hitting the database and basically making the cache for this query
ineffective.
The change to fix this appears to be very simple...
Change line 289 from:
return value == NULL_OBJECT ? null : value;
To simply:
return value;
The code that calls CacheModel.getObject() in CachingStatement already checks
to NULL_OBJECT return values and handles them appropriately so it looks like
this scenario has already been thought through but possibly the above suggested
change was missed.
Attached is a test case that shows the defect and should pass once the above
change is made.
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