Json: map non-primitive non-Dictionary collections to JSON objects

[maumar]

Currently collections are mapped to JSON arrays, we could map them to JSON objects instead.

[roji]

@maumar can you provide some context on what this means?

[AndriySvyryd]

This would allow to map collections of owned types as objects where one of the properties on the owned type is mapped to the object key and the value contains another JSON object containing the rest of the properties.
In the client side it would still be a regular collection, as opposed to #21262

[roji]

Am noting that while this is technically possible, I'm not aware of anyone actual doing this (or requesting it). Significantly, AFAIK neither System.Text.Json nor Newtonsoft.Json support this mode (not out of the box in any case), which should be a pretty strong signal. If nobody's doing this with JSON outside of the database, I'm not sure why it would be needed in the database specifically.

Also, such a mapping cannot be ordered, since JSON objects are generally unordered, and binary representations of JSON (e.g. jsonb in PostgreSQL, but also in other databases) very explicitly do not preserve ordering. Even where they do, there is generally no operation for accessing the Nth key of an object, based on the object layout. We could, of course, support this as an unordered collection (similar to foreign-key-based relationships in non-JSON relational databases), but then the natural way to represent this would be via a Dictionary, no?

To summarize, I think it's an interesting theoretical thought, but I'm not sure what the purpose of such a mapping would be, and why users would want it.