On 03/07/2020 16:21, Pedro Ferreira wrote:
> Hi,
>
> I was wondering if there's some way to create some sort of a "virtual"
> model which is not based on an actual table?
>
> Use case: I have a model (e.g. `Room`) which contains a `data` JSONB
> attribute/column which is supposed to store plugin-specific data. I
> would like plugin code to be able to create a "virtual" model which
> references `Room` 1-to-1 and injects a `plugin_data` backref into it.
> That means I would be able to do `room.plugin_data.user`, for instance,
> which would use `room.data['user_id']` to fetch a `User` object.
Spyne contains some work towards that goal.
I added an example[1]. What works: the Preferences object gets
serialized to json and stored as jsonb. It's also deserialized from json
to an instance when read. It's implemented as a generic UserDefinedType[2].
Caveats:
1. It's postgresql-only (never tested on other RDBMS, maybe it'll work!
help is welcome)
2. It doesn't do fancy orm stuff like mapping the value of a user_id
field to a user instance.
3. Doesn't automatically mark stuff dirty as a field in the subobject
changes[3].
4. Doesn't support marking subfields dirty -- When the subobject is
marked as dirty (using flag_dirty[4]), the whole json document is
updated instead of just the changed subfield. (using jsonb_set[5]).
Disclaimer: I'm the author of Spyne.
I hope it helps!
Best,
Burak
[1]:
https://github.com/arskom/spyne/blob/bc8c3567992abcc387c135d5f8e19c76439c2482/examples/sql/sql_crud.py#L60
[2]:
https://github.com/arskom/spyne/blob/bc8c3567992abcc387c135d5f8e19c76439c2482/spyne/store/relational/document.py#L187
[3]:
https://github.com/arskom/spyne/blob/bc8c3567992abcc387c135d5f8e19c76439c2482/spyne/test/test_sqlalchemy.py#L148
[4]:
https://docs.sqlalchemy.org/en/13/orm/session_api.html#sqlalchemy.orm.attributes.flag_dirt
[5]:
https://www.postgresql.org/docs/12/functions-json.html#FUNCTIONS-JSON-PROCESSING-TABLE
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