DB2 - DbJson length, treat length = 4000+ as LOB type for DB2

[rPraml]

Hello @rbygrave,

this fixes the

TestJsonMapBasic.whereManyPredicateDb2:76 » Persistence Query threw SQLException:DB2 SQL Error: SQLCODE=-134, SQLSTATE=42907

I've bisected and it was introduced by this commit: 11c9bdf because it changes EBasicJsonMap.content property from @DbJson to

  @DbJson(length = 5000)
  Map<String, Object> content;

The problem is, that a field with value of length 5000 is no longer detected as lob. And lob fields are not allowed in DB2 distinct queries...
We've added a workaround for this some time ago: #2511
Unfortunately, the detection mechanism is not precise enough. So as quick workaround (!) I added to the "isDbLob" a check if the dbLength > 255

I'm not happy with this check, because there is also a "use best type detection" here: #3107 so that lengths > 4000 are mapped to lob instead to varchar.

So from DB2 perspective, it would be better to use dbLength > 4000 as fix ?

I could either refactor the whole "unselectLobs" code to "unselectLobsForDb2". "isDbLob" -> "isDb2Lob" ans so on. So I can use hard coded values.
(All in all, distincts and lobs are very annoying in DB2 and it seems that this is really only needed for DB2 and maybe Oracle? - see comment here)

OR

I find a way to determine the exact DDL type from a BeanProperty, but this is not easily to determine, because it is hidden in "renderDbType" and so on.

in short words, the easiest fix would be to assume that a DbJson is a lob if dbLength > 4000. What do you think about this?

cheers
Roland

[rob-bygrave]

assume that a DbJson is a lob if dbLength > 4000.

That sounds reasonable to me.

[rbygrave]

• Use 4000 to match the DB2 logic for considering a column a lob (for distinct etc)
• Rename distinctNoLobs -> platformDistinctNoLobs
• Rename isDbLob() -> isLobForPlatform()
• Rename unselectLobs() -> unselectLobsForPlatform()