Complex usage of jinja with dbt

Case Study: Building E-Commerce Data Models with dbt

Susan Sun

Freelance Data Scientist

Jinja statement: loop

Jinja statements are enclosed in {% %}:

Looping through items

Template:
```
{% for ... %} ... {% endfor %}
```

Example:

{% for order_status in order_statuses %}
  SUM(
      CASE WHEN status = '{{ order_status }}' 
        THEN order_id 
      END)
{% endfor %}

Jinja statement: loop

Repeating SQL:

SELECT 
    user_id,
    SUM(CASE WHEN status = 'Shipped' THEN 1 ELSE 0 END) 
        AS num_orders_Shipped,
    SUM(CASE WHEN status = 'Complete' THEN 1 ELSE 0 END) 
        AS num_orders_Complete,
    SUM(CASE WHEN status = 'Processing' THEN 1 ELSE 0 END) 
        AS num_orders_Processing,        
FROM {{ ref('stg_looker__orders') }}
GROUP BY 1

Jinja statement: loop

{% set order_statuses = ['Shipped', 'Complete', 'Processing'] %}

SELECT 
    user_id,
    -- Jinja loop
    {% for order_status in order_statuses %}
        SUM(CASE WHEN status = '{{ order_status }}' THEN 1 ELSE 0 END) 
        -- Parametrized column name
        AS num_orders_{{ order_status }}
    {% endfor %}
FROM {{ ref('stg_looker__orders') }}
GROUP BY 1

Jinja statement: loop

dbt compile output:

SELECT 
    user_id,
    SUM(CASE WHEN status = 'Shipped' THEN 1 ELSE 0 END) 
        AS num_orders_Shipped,
    SUM(CASE WHEN status = 'Complete' THEN 1 ELSE 0 END) 
        AS num_orders_Complete,
    SUM(CASE WHEN status = 'Processing' THEN 1 ELSE 0 END) 
        AS num_orders_Processing,        
FROM "dbt"."main"."stg_looker__orders"
GROUP BY 1

Jinja statement: macros

A Jinja macro:

Is a function, written in Jinja
Is reusable
Is stored in the /macros folder

COALESCE():

returns the first non-null value
syntax: COALESCE(value1, value2, ...)
e.g. COALESCE(nickname, first_name)

An example of a macro function:

A screenshot of the IDE, with the `coalesce_and_round.sql` file open in the IDE editor showing its macro logic.

Jinja statement: macros

Jinja statements are enclosed in {% %}:

A reusable macro function:

Template:
```
{% macro ... %} ... {% endmacro %}
```

Example:

{% macro coalesce_and_round(column_name, decimal_places = 2) %}
      ROUND(COALESCE({{ column_name }}, 0), {{ decimal_places }})
{% endmacro %}

Jinja statement: macros

Repeated SQL

ROUND(COALESCE(sales_amount, 0), 2) AS sales_amount,
ROUND(COALESCE(cost_of_goods_sold, 0), 2) AS cost_of_goods_sold,

DRY (Don't Repeat Yourself)

Create macro called coalesce_and_round.sql
Store in /macros

Invoke:

{{ coalesce_and_round('sales_amount', 2) }} AS sales_amount,
{{ coalesce_and_round('cost_of_goods_sold', 2) }} AS cost_of_goods_sold,

Managing Jinja whitespace

As written:

{% set traffic_source_values = ['Adwords', 'Email', 'Facebook'] %}
{% set browser_values = ['Chrome', 'Firefox', 'Safari', 'IE', 'Other'] %}

SELECT 
    user_id,
    COUNT(DISTINCT session_id) AS num_web_sessions,
...

Managing Jinja whitespace

Compiled:




SELECT 
    user_id,
    COUNT(DISTINCT session_id) AS num_web_sessions,
...

Managing Jinja whitespace

{%- ... %} strips the whitespace before.
{% ... -%} strips the whitespace after.
{%- ... -%} strips both.
An example:

{%- set traffic_source_values = ['Adwords', 'Email', 'Facebook'] -%}
{%- set browser_values = ['Chrome', 'Firefox', 'Safari', 'IE', 'Other'] -%}

SELECT 
    user_id,
    COUNT(DISTINCT session_id) AS num_web_sessions,
...

Let's practice!

Case Study: Building E-Commerce Data Models with dbt