Built-in Jinja context variables in dbt - Mini Project: Build & Apply

Exploring Built-in Jinja Context Variables in dbt

📖 Scenario: You are working on a dbt project to build data models. You want to understand how to use built-in Jinja context variables to make your models dynamic and informative.

🎯 Goal: Learn to access and display built-in Jinja context variables in dbt models to understand the current model's metadata.

📋 What You'll Learn

Create a variable to hold the model name using the built-in Jinja variable

Create a variable to hold the model's unique identifier using the built-in Jinja variable

Use a Jinja for loop to list all columns available in the model using the built-in context variable

Print the model name, unique identifier, and list of columns

💡 Why This Matters

🌍 Real World

In real dbt projects, these built-in variables help you write dynamic models that adapt to different environments and provide metadata for debugging.

💼 Career

Understanding Jinja context variables is essential for dbt developers and data engineers to build maintainable and flexible data transformation pipelines.

1

Create a variable for the model name

Create a variable called model_name and set it to the built-in Jinja context variable this.name which holds the current model's name.

dbt

# Your code here

Hint

The variable this gives info about the current model. Use this.name to get the model's name.

2

Create a variable for the model's unique identifier

Create a variable called model_id and set it to the built-in Jinja context variable this.identifier which holds the unique identifier of the current model.

dbt

{% set model_name = this.name %}
# Your code here

Hint

Use this.identifier to get the unique id of the model.

3

List all columns in the model

Create a variable called column_names that uses a Jinja for loop over columns to collect all column names into a list.

dbt

{% set model_name = this.name %}
{% set model_id = this.identifier %}
# Your code here

Hint

The columns variable holds all columns. Use a for loop to get each col.name.

4

Print the model info and columns

Print the model_name, model_id, and the list column_names using Jinja's print or log statements.

dbt

{% set model_name = this.name %}
{% set model_id = this.identifier %}
{% set column_names = [] %}
{% for col in columns %}
  {% do column_names.append(col.name) %}
{% endfor %}
# Your code here

Hint

Use {{ variable }} to display variables in Jinja templates.

Practice

1. What does the built-in Jinja context variable run_started_at provide in dbt?

easy

A. The total number of models in the project

B. The name of the current model being executed

C. The timestamp when the current dbt run started

D. The database connection string

Solution

1. Step 1: Understand the purpose of run_started_at

   This variable holds the timestamp marking the start of the dbt run.

2. Step 2: Compare with other options

   Other options describe unrelated information like model name or connection details.

3. Final Answer:

   The timestamp when the current dbt run started -> Option C

4. Quick Check:

   run_started_at = Timestamp [OK]

Hint: Remember: run_started_at = run start time [OK]

Common Mistakes:

• Confusing run_started_at with model name
• Thinking it gives database info
• Assuming it counts models

2. Which of the following is the correct syntax to access the current model name using a built-in Jinja context variable in dbt?

easy

A. {{ this.name }}

B. {{ model_name }}

C. {{ this.model }}

D. {{ current_model }}

Solution

1. Step 1: Recall the correct variable for current model

   The variable this refers to the current model, and this.name gives its name.

2. Step 2: Check syntax correctness

   Only {{ this.name }} correctly accesses the model name in Jinja syntax.

3. Final Answer:

   {{ this.name }} -> Option A

4. Quick Check:

   Current model name = {{ this.name }} [OK]

Hint: Use this.name for current model name [OK]

Common Mistakes:

• Using undefined variables like model_name
• Missing dot notation after this
• Using incorrect variable names

3. Given the following dbt Jinja code snippet, what will be the output of {{ invocation_id }}?

{% set id = invocation_id %}{{ id }}

medium

A. The number of models executed so far

B. A unique identifier string for the current dbt run

C. The current timestamp

D. An error because invocation_id is undefined

Solution

1. Step 1: Understand what invocation_id represents

   This variable holds a unique string ID for the current dbt run invocation.

2. Step 2: Analyze the code snippet

   The code sets id to invocation_id and then outputs it, so it prints the unique run ID.

3. Final Answer:

   A unique identifier string for the current dbt run -> Option B

4. Quick Check:

   invocation_id = Unique run ID [OK]

Hint: invocation_id = unique run ID string [OK]

Common Mistakes:

• Thinking it counts models
• Confusing with timestamps
• Assuming it causes an error

4. You wrote this dbt Jinja code but get an error:

{{ run_started_at.strftime('%Y-%m-%d') }}

. What is the likely cause?

medium

A. run_started_at is a string, not a datetime object, so strftime fails

B. Missing parentheses after run_started_at

C. strftime is not a valid method in Jinja

D. You must use single curly braces instead of double

Solution

1. Step 1: Check the type of run_started_at

   In dbt, run_started_at is a string timestamp, not a datetime object.

2. Step 2: Understand why strftime fails

   Since it's a string, calling strftime (a datetime method) causes an error.

3. Final Answer:

   run_started_at is a string, not a datetime object, so strftime fails -> Option A

4. Quick Check:

   String type blocks datetime methods [OK]

Hint: run_started_at is string; convert before datetime methods [OK]

Common Mistakes:

• Assuming run_started_at is datetime
• Using single braces for Jinja variables
• Thinking strftime is unsupported in Jinja

5. You want to create a dbt model that adds a column with the current run's unique ID and the run start date in 'YYYY-MM-DD' format. Which Jinja code snippet correctly uses built-in context variables to achieve this?

hard

A. {% set run_date = run_started_at.split('-')[0] %}
SELECT *, '{{ invocation_id }}' AS run_id, '{{ run_date }}' AS run_date FROM {{ this }}

B. {% set run_date = run_started_at.strftime('%Y-%m-%d') %}
SELECT *, '{{ invocation_id }}' AS run_id, '{{ run_date }}' AS run_date FROM {{ this }}

C. SELECT *, '{{ invocation_id }}' AS run_id, '{{ run_started_at }}' AS run_date FROM {{ this }}

D. {% set run_date = run_started_at[:10] %}
SELECT *, '{{ invocation_id }}' AS run_id, '{{ run_date }}' AS run_date FROM {{ this }}

Solution

1. Step 1: Extract date from run_started_at string

   Since run_started_at is a string like 'YYYY-MM-DDTHH:MM:SS', slicing the first 10 characters gets the date.

2. Step 2: Use invocation_id and run_date in SELECT

   The snippet correctly sets run_date and uses both variables in the SELECT statement.

3. Step 3: Check other options for errors

   {% set run_date = run_started_at.strftime('%Y-%m-%d') %} SELECT *, '{{ invocation_id }}' AS run_id, '{{ run_date }}' AS run_date FROM {{ this }} tries to use strftime on a string (error). SELECT *, '{{ invocation_id }}' AS run_id, '{{ run_started_at }}' AS run_date FROM {{ this }} uses full timestamp, not formatted date. {% set run_date = run_started_at.split('-')[0] %} SELECT *, '{{ invocation_id }}' AS run_id, '{{ run_date }}' AS run_date FROM {{ this }} extracts only year incorrectly.

4. Final Answer:

   Extracts date with run_started_at[:10] and uses invocation_id -> Option D

5. Quick Check:

   Slice string for date, use invocation_id [OK]

Hint: Slice run_started_at[:10] for date, use invocation_id [OK]

Common Mistakes:

• Using strftime on string variable
• Not formatting run_started_at to date
• Extracting only year instead of full date