Update for v0.19: Result, response objects

[jtcohen6]

Description & motivation

Thanks to @clrcrl, I realized this evening (dbt-labs/dbt-utils#319 + dbt-labs/dbt-utils#320) that the call statement object has very subtly changed in dbt v0.19.0.

Instead of returning a status, the call statement block now returns an adapter-specific response which includes the same basic info in a structured format, while still rendering to the same thing status used to, via its _message attribute. I'd say this is a big improvement overall!

{
    'response': BigQueryAdapterResponse(_message='OK', code=None, rows_affected=None, bytes_processed=None),
    'data': [(Decimal('1'),)],
    'table': <agate.table.Table object at 0x111ceafd0>
}

It's also a potentially breaking change for macros, materializations, packages (e.g. dbt_utils.insert_by_period, dbt_external_tables.stage_external_sources) that hook right into the statement['status'] field. It should be as simple as switching this from statement['status'] to statement['response']. Or, to be compatible both ways:

{% set my_msg = statement['response'] if 'response' in statement.keys() else statement['status'] %}

While I was there, I realized that I'd failed to update the "dbt Classes" Result object docs. I... had also kind of forgotten these docs existed. They were still linking to a JSON Schema that went away in v0.15.0. I think the whole "dbt Classes" docs could use some love.

To-do before merge

Pre-release docs

Is this change related to an unreleased version of dbt?

• Yes: please
  • update the base branch to next
  • add Changelog components: <Changelog>[New/Changed] in v0.x.0</Changelog>
  • add links to the "New and changed documentation" section of the latest Migration Guide
• No: please ensure the base branch is current
• Unsure: we'll let you know!

[clrcrl]

Small pieces of feedback, otherwise LGTM

[clrcrl]

Hanging comma, should this be a period instead?

[jtcohen6]

ty for catching!

[clrcrl]

I know this is a PR for next, but schemas.getdbt.com doesn't have any content — is that expected for now?

[jtcohen6]

yup, expected for now — it'll have something there by the time of final release (: