DynamicDto

The Kotlin side of the dynamic_dto composite: a discriminator and a JSON payload.

A COMPOSITE type says at schema level what shape a column holds, which is right where the shape is fixed and wrong where it is not. dynamic_dto is the other case - one column holding whichever of several unrelated shapes this row happens to carry, with type_name saying which.

Neither direction needs this type to be named. A dynamic_dto column comes back as the registered class itself, and a column holding several of them comes back as their common supertype; going the other way, an instance of a registered class is written as one on the terms DynamicTypes.strategy sets. What this type is for is the two places inference does not reach: a value whose destination is ambiguous because its class is registered as a composite as well, and a caller who wants the payload as it is stored rather than as a class.

DynamicTypes.toDynamicDto is the only way to make one, which is what keeps the discriminator honest. A name is checked against the registry there and nowhere else - the column is a plain (text, jsonb) and the server has never heard of the registry, so a value built with a name nothing is registered under would store cleanly and fail on whichever read reached it first, in some other process, much later.