Dbt Quick Patterns — Macros Part 2

Yes, Debug Mode Exists… If You Create It.

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I spent a lot of effort crafting log messages and worrying about whether they should write to the console or just to file. Looking back, I’m a bit embarrassed. Why not simply use debug mode and control log messages at run time?

While dbt does have debug and log-level arguments, they don’t help with the log messages we write. We have no way to specify a level in the log() macro. In fact, the only configuration for log() is info=true or info=false. So what to do? What to do?

Now to the embarrassing part. We can simply use vars() or envars() to pass in the value for info. It took me years to figure this out. The macro below uses var(), but it would be just as easy to use envar() or both to add flexibility.

{% macro generate_columns() %}
    {% if not execute %}
        return('')
    {% endif %}

    {# Defaults to false #}
    {% set info = var('debug', False) %} 

    {# Contrived code to select columns from a table #}
    {% set metrics = [
        'total_sales',
        'yoy_sales',
        'ytd_sales'
    ]%} 

    {% set columns %}
        {% for metric in metrics %}
            {# Control whether we log to console or not #}
            {{ log('Generating ' + metric, info=info) }}
            {{ metric }} {% if not loop.last %},{% endif %}
        {% endfor%} 
    {% endset %}

    {{ return(columns) }}
{% endmacro %}