[feature] Optionally suppress keys with null values

[kostmo]

Apparently, such a feature is available in the Data.Aeson.TH module (see omitNothingFields), but that module requires that TemplateHaskell be enabled.

[informatikr]

This should be done in the ToJSON instance.

omitNothingFields exists for TemplateHaskell and DeriveGeneric. Or if you write your own ToJSON instance, you can do it there.

[kostmo]

I do now see omitNothingFields in the Data.Aeson.Types module in addition to the Data.Aeson.TH module.

However, I currently have over 50 records (with this number expected to grow) which require serialization to JSON, so the cost of additional per-record boilerplate is high.

With my modification to aeson-pretty to suppress nulls, I am able to get by with only a single, short line per record to declare each as an instance of ToJson:

instance ToJSON MyModule.MyRecord

Unless I am missing something, without having aeson-pretty handle it, the per-record boilerplate increases to this:

instance ToJSON MyModule.MyRecord where
    toJSON = genericToJSON defaultOptions { omitNothingFields = True }

Although this is a 100% increase in lines for me (more in terms of tokens), perhaps this amount of boilerplate doesn't earn me any sympathy.

[chris-martin]

Wouldn't it make more sense to write a function

removeNullValues :: Value -> Value

and then encode your value with encodePretty . removeNullValues . toJSON instead of encodePretty?

[philderbeast]

Wouldn't it make more sense to write a function

The stripNulls example from aeson-extras does exactly this, https://github.com/phadej/aeson-extra/pull/57.