Hierarchical models in dbt

Introduction to dbt

Mike Metzger

Data Engineer

What is a hierarchy in dbt?

• Represents the dependencies within a dbt project
• Also known as a directed acyclic graph (DAG), or lineage graph
  • Note this being specific to dbt, rather than general DAG
• Allows models to be built / updated according to dependencies

Hierarchy details

• avg_fare_per_day and total_creditcard_riders_per_day depend on taxi_rides_raw
• dbt builds taxi_rides_raw first
• dbt creates entries alphabetically without a lineage graph
  • avg_fare_per_day would fail without taxi_rides_raw

How are hierarchies defined?

• Built using the Jinja template language in the model file(s)
• Most often using the ref function
• Replace table name with {{ ref('model_name') }} in SQL
• (Re-)Materialize table with dbt run
• ref templates are substituted with actual table names

Hierarchy example

SELECT 
  first_name, last_name
FROM taxi_rides_raw

SELECT 
  first_name, last_name
FROM {{ ref('taxi_rides_raw') }}

Let's practice!

Introduction to dbt