Clob mapping not working with mysql

Question

Hi,
I have an application that i'm running with MySQL and Oracle at the same
time. At some point, i need to use a 'clob' mapping. When i do this, it
just works fine with oracle but it fails with mysql. i have the exception:
Field "com.ennov.prisma.api.document.jdo.AbstractDocumentPO.description"
is mapped as a clob, but should be represented as a different mapping.
If the field is a string and you would like to force it to map as a
clob, add an extension to its field metadata with a key of "jdbc-size"
and a value of
-1.[com.ennov.prisma.api.document.jdo.AbstractDocumentPO.description]
     at kodo.jdbc.meta.Mappings.invalidMapping(Mappings.java:132)
     at kodo.jdbc.meta.Mappings.invalidMapping(Mappings.java:118)
     at
kodo.jdbc.meta.ClobFieldMapping.fromMappingInfo(ClobFieldMapping.java:46)
if i use a value mapping, it works with MySQL but fails with Oracle (I
have sql error because a clob is used in a distinct select).
In the manual, it is written "Note that some databases can support
string of unlimited length without using a CLOB; when this is the case
the mapping tool will install a value mapping in favor of
this mapping.". So apparently, this is not the case with MySQLDictionary.
To solve my problem and have my code working with both databases, i had
to extend the MySQLDictionary and overwrite the replaceFieldMapping
method in order to replace the clob mapping by a value mapping at
runtime but i don't feel confident to do this kind of modifications by
mysel and would expect this behaviour to be solved quite soon.
Thanks for your help since this problem is urgent for us,
Laurent Czinczenheim

Answer 1

Laurent-
The best solution would probably be to just have separate mappings for
the MySQL and Oracle databases. The easiest way to accomplish this would
be to have a separate setting for each of the databases. E.g.:
kodo.jdbc.meta.MappingFactory: file(SingleFile=true, FileName=oracle.mapping)
kodo.jdbc.meta.MappingFactory: file(SingleFile=true, FileName=mysql.mapping)
That way, you can use a clob mapping for Oracle, and a normal value
mapping for MySQL (since MySQL doesn't need to use the CLOB mapping, and
it isn't very efficient).
For more details on this, see:
http://docs.solarmetric.com/manual.html#ref_guide_mapping_factory
Another solution is to just stick with your custom extension of the
MySQLDictionary, which is a perfectly valid way of having special CLOB
handling in MySQL. Note, though, that CLOB handling is less efficient
than VARCHAR handling, so it should be a mapping of last resort, and
there isn't any need to use it in MySQL.
In article <[email protected]>, czinczenheim wrote:
Hi,
I have an application that i'm running with MySQL and Oracle at the same
time. At some point, i need to use a 'clob' mapping. When i do this, it
just works fine with oracle but it fails with mysql. i have the exception:
Field "com.ennov.prisma.api.document.jdo.AbstractDocumentPO.description"
is mapped as a clob, but should be represented as a different mapping.
If the field is a string and you would like to force it to map as a
clob, add an extension to its field metadata with a key of "jdbc-size"
and a value of
-1.[com.ennov.prisma.api.document.jdo.AbstractDocumentPO.description]
     at kodo.jdbc.meta.Mappings.invalidMapping(Mappings.java:132)
     at kodo.jdbc.meta.Mappings.invalidMapping(Mappings.java:118)
     at
kodo.jdbc.meta.ClobFieldMapping.fromMappingInfo(ClobFieldMapping.java:46)
if i use a value mapping, it works with MySQL but fails with Oracle (I
have sql error because a clob is used in a distinct select).
In the manual, it is written "Note that some databases can support
string of unlimited length without using a CLOB; when this is the case
the mapping tool will install a value mapping in favor of
this mapping.". So apparently, this is not the case with MySQLDictionary.
To solve my problem and have my code working with both databases, i had
to extend the MySQLDictionary and overwrite the replaceFieldMapping
method in order to replace the clob mapping by a value mapping at
runtime but i don't feel confident to do this kind of modifications by
mysel and would expect this behaviour to be solved quite soon.
Thanks for your help since this problem is urgent for us,
Laurent Czinczenheim
Marc Prud'hommeaux
SolarMetric Inc.