using model.columns in dbt

using-model-columns-in-dbt.sql

the view definition
```sql 
-- target_view.sql
{%- set frame = 'OVER (PARTITION BY transaction_id ORDER BY id DESC)' -%}
SELECT DISTINCT
    transaction_id
{%- for f in model['columns'] -%}
  {% if f != 'transaction_id' %}
  , FIRST_VALUE({{ f }}) {{ frame }} AS {{ f }}
  {%- endif -%}
{% endfor %}
  , ROUND(DATE_DIFF(
        'day'
      , FIRST_VALUE(purchase_date) {{ frame }}
      , FIRST_VALUE(expires_date) {{ frame }}
    ) / 30.4) AS purchase_duration_months
FROM {{ ref('src_purchases_table') }}
WHERE deleted_at IS NOT NULL
```
the model definition in the schema.yml file
```yaml
# schema.yml
models:
  - name: target_view
    columns:
      - name: column1
      - name: transaction_id
      - name: id
      - name: user_id
      - name: purchase_date
      - name: expires_date
```
the compiled output 
```sql
-- target/compiled/project/target_view.sql
SELECT DISTINCT
    transaction_id
  , FIRST_VALUE(column1) OVER (PARTITION BY transaction_id ORDER BY id DESC) column1
  , FIRST_VALUE(id) OVER (PARTITION BY transaction_id ORDER BY id DESC) id
  , FIRST_VALUE(user_id) OVER (PARTITION BY transaction_id ORDER BY id DESC) user_id
  , ROUND(DATE_DIFF(
        'day'
      , FIRST_VALUE(purchase_date) OVER (PARTITION BY transaction_id ORDER BY id DESC)
      , FIRST_VALUE(expires_date) OVER (PARTITION BY transaction_id ORDER BY id DESC)
    ) / 30.4) AS purchase_duration_months
FROM source.src_purchases_table
```