I have an odd requirement that I have not yet stum...

# exposed

[Tommi Lepola]

I have an odd requirement that I have not yet stumbled upon, since I'm more of a front-end orienteered fellow. How would you turn this into Exposed objects and Kotlin interfaces?
• In the UI there's a list, where you can add items to. The items are supposed to be turned into rows in the database table(s)
• The problem:
◦ The items have fields, like Name, Tag, Value. The items also have a Type field. The Type field dictates the rest of the fields for the item.
▪︎ So the Name, Tag and Value are independent of the Type field.
▪︎ But if the value of Type is Type A, a few more fields are added for the item: IP, Port, Channel. However, if the Type has the value Type B, the item has other fields added to it: Address, Body, Method
• The question:
◦ What kind of table(s) with what kinds of fields would you turn this spec into?
▪︎ One option would be to create one table where all Type dependent values (IP, Port, Channel, Address, Body, Method) are nullable.
▪︎ Another option would be to create add a field into table for the item such as TypeDependentFields, which would then be an object/class which would contain either IP, Port, Channel or Address, Body, Method.
• For example in TypeScript this could be achieved with union types: TypeDependentFields: TypeAFields | TypeBFields, but Kotlin doesn't have union types.
• It'd be nice to have this kind of datamodel atleast between the frontend (React TypeScript) and the backend for simplicity
• Tech stack: Kotlin, Ktor, Exposed, PostgreSQL

[Endre Deak]

1. you can use an entity-attribute-value schema for this
2. you can use exposed to read up raw attributes with values
3. you need the different types defined as classes somewhere, and some factory methods which can take the exposed result and turn them to an actual type instance
(at least that's what I'd do after a brief first read)

[Tommi Lepola]

Thanks! Someone else recommended this at another Slack as well, and it seems like this is the way to go 🙂 I might ask for some more details later when I get to play around with the idea some more, but at least this helps me to get going!