Looping

Jinja2 loops allow you to iterate over data structures and conditionally include elements in your YAML files. This is particularly useful for:

• Generating configurations for multiple environments or instances
• Conditional inclusion based on environment variables or external data
• Dynamically constructing complex nested structures

Jinja2 Loop Basics

Before diving into examples, let's review the basic syntax for Jinja2 loops:

• For Loop: {% for item in iterable %} ... {% endfor %}
• While Loop: Jinja2 does not natively support while loops, but you can mimic their behavior using for loops and conditions.

Examples

Iterating Over a List

Generate a list of users in a YAML configuration.

Example

YAML with Jinja2Rendered YAML

traces:
  {%- for user in ['Alice', 'Bob', 'Charlie'] %}
  - name: "{{ user }}_weekly_orders_trace"
    type: bar 
    model: ref('orders')
    props:
      x: query( date_trunc('week', created_at) )
      y: query( orders )
    filters:
      - query( user = '{{ user }}' )
  {%- endfor %}

traces:
  - name: "Alice_weekly_orders_trace"
    type: bar 
    model: ref('orders')
    props:
      x: query( date_trunc('week', created_at) )
      y: query( orders )
    filters:
      - query( user = 'Alice' )
  - name: "Bob_weekly_orders_trace"
    type: bar 
    model: ref('orders')
    props:
      x: query( date_trunc('week', created_at) )
      y: query( orders )
    filters:
      - query( user = 'Bob' )
  - name: "Charlie_weekly_orders_trace"
    type: bar 
    model: ref('orders')
    props:
      x: query( date_trunc('week', created_at) )
      y: query( orders )
    filters:
      - query( user = 'Charlie' )

Nested Loops for Hierarchical Structures

Create a nested structure of departments and employees.

Example

YAML with Jinja2Rendered YAML

departments:
  {% for department, employees in {'Sales': ['Alice', 'Bob'], 'Engineering': ['Charlie', 'Dave']}.items() %}
  - department: "{{ department }}"
    employees:
      {% for employee in employees %}
      - name: "{{ employee }}"
      {% endfor %}
  {% endfor %}

departments:
  - department: "Sales"
    employees:
      - name: "Alice"
      - name: "Bob"
  - department: "Engineering"
    employees:
      - name: "Charlie"
      - name: "Dave"