[Bug] adapter.get_columns_in_relation does not work with materialized views

[rubenhelsloot]

Is this a new bug?

• [X] I believe this is a new bug
• [X] I have searched the existing issues, and I could not find an existing issue for this bug

Current Behavior

When I use dbt_utils.star() to list the columns of a materialized view, it renders /* no columns returned from star() macro */ instead. I looked into it and found that adapter.get_columns_in_relation returns an empty list.

I believe this is because the relation is a materialized view, and adapter.get_columns_in_relation only returns the columns of tables.

Expected Behavior

I would expect the construct to work for materialized views as well.

Steps To Reproduce

1. Create a postgres project;
2. Create a materialized view with some columns;
3. In a new model, try to get the columns of the materialized view.

Relevant log output

No response

Environment

- OS: MacOS
- Python: 3.11
- dbt-postgres: 1.7.7

Additional Context

No response

[rubenhelsloot]

As a temporary workaround, I've overwritten postgres__get_columns_in_relation like this:

-- Override get_columns_in_relation to work with materialized views

{% macro postgres__get_columns_in_relation(relation) -%}
  {% call statement('get_columns_in_relation', fetch_result=True) %}
      with from_table AS (
          select
              column_name,
              data_type,
              character_maximum_length,
              numeric_precision,
              numeric_scale

          from {{ relation.information_schema('columns') }}
          where table_name = '{{ relation.identifier }}'
              {% if relation.schema %}
              and table_schema = '{{ relation.schema }}'
              {% endif %}
          ORDER BY ordinal_position
      ),

      from_matview AS (
          select
              attname AS column_name,
              pg_catalog.format_type(
                pg_attribute.atttypid,
                pg_attribute.atttypmod
              ) AS data_type,
              NULL::int AS character_maximum_length,
              38 AS numeric_precision,
              9 AS numeric_scale

          FROM pg_attribute
            JOIN pg_class on pg_attribute.attrelid = pg_class.oid
            JOIN pg_namespace on pg_class.relnamespace = pg_namespace.oid
          WHERE pg_attribute.attnum > 0
              AND NOT pg_attribute.attisdropped
              AND pg_class.relname = '{{ relation.identifier }}'
              {% if relation.schema %}
              AND pg_namespace.nspname = '{{ relation.schema }}'
              {% endif %}
          ORDER BY pg_attribute.attnum
      )

      select *
      FROM from_table
      UNION ALL (
        SELECT *
        FROM from_matview
      )

  {% endcall %}
  {% set table = load_result('get_columns_in_relation').table %}
  {{ return(sql_convert_columns_in_relation(table)) }}
{% endmacro %}

[dbeatty10]

Thanks for reporting this @rubenhelsloot !

This looks the same as https://github.com/dbt-labs/dbt-core/issues/9419, so I'm going to close this as a duplicate.

Your workaround might work, but I'd recommend this instead for full-backwards compatibility: https://github.com/dbt-labs/dbt-core/issues/9419#issuecomment-1907067697.