[GitHub] [hive] belugabehr commented on pull request #1118: HIVE-23363: Upgrade DataNucleus dependency to 5.2

[GitBox <gi...@apache.org>]

belugabehr commented on pull request #1118:
URL: https://github.com/apache/hive/pull/1118#issuecomment-652546609


   @ashutoshc Let me see if I can address all of your questions with some background and context.  It took me a long time to get these changes to pass the unit tests.
   
   So, these mappings, in some respect, don't really matter.  When HMS is started, users use the `schema-tool` to create the HMS schema for real.  Some of these mappings in the `jdo` file (like indexes) are only applied when unit testing because the unit tests build the schema via DN and `datanucleus.schema.autoCreateAll`.  For unit testing, the database backend is Apache Derby.  I changed the name of the index to match the Derby schema more closely.  In trying to debug these various errors, I was very confused at first about it complaining about "COLUMNS_PK".
   
   https://github.com/apache/hive/blob/4942a7c0b4be3a5b0c889a89b903e9a70c57d494/standalone-metastore/metastore-server/src/main/sql/derby/hive-schema-4.0.0.derby.sql#L364
   
   With that said, when I upgraded to DN 5.x, the unit tests would not pass.  I narrowed the issue down to this one table definition.  I tried several iterations to get success, but this is the one that worked.  I derived this solution by closely examining the docs on this topic.  It has an example that very closely aligns with this use case:
   
   http://www.datanucleus.org/products/accessplatform/jpa/mapping.html#embedded_collection
   
   It is a bit of a wonder looking at the existing JDO definition how this ever worked.
   
   ```
             <primary-key name="COLUMNS_PK">
               <column name="COLUMN_NAME"/>
             </primary-key>
   ```
   
   This is not correct, this should be a compound primary key of CD_ID *and* COLUMN_NAME.  This is enforced by `SQL110922153006740` in the full schema.  As things currently stand, the COLUMN_NAME definition in the `jdo` file says that the COLUMN_NAME is not defined to be non-null.  This caused an error with Derby as it didn't allow creating a PRIMARY KEY on a field that could be null.
   
   So, putting it all together, I came to the current solution.


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