You don't need to care about introducing a breaking change in the app. I'm fine with raising the minimum backend version for this. This should make deserialization way easier.

One thing I noticed: Make sure that the fromJson method can take the output of the toJsonWithId. As for offline use, I often use these together. This means for serializing the DateTime we should probably use date.toUtc().millisecondsSinceEpoch. This makes it consistent with the Expense DateTime as well. (I know this isn't as nice in the backend since marshmallow has no field for it)

Thanks for your feedback, @TomBursch . I didn't know about the interference with toJsonWithId, so I hope I did it right now.

Another word of caution: I'm not a web developer and so I'm not always familiar with the Null Constraints of dart. Hence, please have a good look at every question or exclamation mark I use for e.g. a DateTime? data type.

Hey @crosspolar, thanks for the patience. Could you rebase your changes?

@TomBursch , hope that merge is okay. I've used GitHubs "Resolve conflict" button the first time...

(I need to clean it anyway first)

alright, you were faster cleaning 😄

@crosspolar yeah no worries 😄 Thanks again for this, looks really good!