[play 2.4] Json Reads/Writes with more than 22 parameters

[valtteri...@hotmail.com]

Hi!

One of our case classes has 30 constructor parameters and we ran into a problem with Json Reads/Writes. They seem to be able to handle only 22 parameters. Beyond that, you get the error message "No unapply or unapplySeq function found".

I cut away some parameters into their own case class like this:

case class LotsOfParams(params....) -> case class NotSoManyParams(smallerCaseClass, other params....)

But this causes the Json to change form. Now we have:

{

  "smallerCaseClass": { cutParamsHere }

}

Which sucks because our client software is relying on the old format.

Can you suggest of alternative ways of handling the situation, or do I have to manually create a Writes with explicit instructions for all the 30 fields?

Valtteri

[Mariot Chauvin]

http://stackoverflow.com/questions/23571677/22-fields-limit-in-scala-2-11-play-framework-2-3-case-classes-and-functions/23588132#23588132

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[Mariot Chauvin]

As this is not pointed the stackoverflow response, you could also use https://github.com/jto/validation which does not 

suffer from the problem AFAIK, see https://github.com/jto/validation/blob/master/documentation/tut/ScalaValidationMacros.md  

[valtteri...@hotmail.com]

Thank you for the suggestions!

I wonder if the Reads/Writes could be modified some day to use constructor fields instead of apply/unapply as well, like the validation macros. I haven't looked at how exactly the Reads/Writes are implemented now so that's just a though that came to mind.

Time to code now.. prototype towards the most elegant solution.. thanks again :)

Valtteri

[valtteri...@hotmail.com]

You know, after thinking about this a bit, I thought I'd go with explicit instructions for all the 30 fields. It's only a single case class so I don't need a more generic way. So I thought it would be the simplest solution and also easiest to read for others.

But what happened? I can't use Writes because they rely on unapply. So I tried using a plain old Json.obj() - function to construct the Json. There's just a single caveat. Unlike Writes, Json.obj() writes Option None values as nulls. So I googled this and guess what the suggested solution is? To use Writes of course. Back to square one..

Valtteri