Quickbase Pipelines: How to upsert nested JSON array to multi-select text field?

How interesting. I just had to solve this problem the other night.
To get a more succinct Jinja2 expression you'll want to use combinations of following filters:

• selectattr
• map
• join

If I understand your schema correctly, the expression for the first issue (where you are simply writing to a text field) would look like this:

{{ d.custom_fields | selectattr('key', 'eq', 'street') | map(attribute='value') | join('') }}

The second problem may be a little less elegant because there isn't a way that I know of to combine multiple lists using jinja2.
{% for choice in d.custom_fields | selectattr('key', 'eq', 'choices') -%}
{{ choice.value | join(';') -}}
{% if not loop.last %};{% endif -%}
{% endfor -%}

The important part to remember about multi-select text is that a semicolon should be used as a delimiter (unless you are posting the data directly via the RESTful API).

Here is a live parser that allows you to test with json instead of only YAML.
https://j2live.ttl255.com/