Extends

Overview

The extends property allows a cube to inherit measures, dimensions, segments, and joins from another cube. This promotes code reusability and keeps your data model DRY.

Example

cubes:
  # Base cube with shared members
  - name: base_events
    sql_table: events

    measures:
      - name: count
        type: count

    dimensions:
      - name: id
        type: number
        sql: "\{CUBE\}.id"
        primary_key: true

      - name: created_at
        type: time
        sql: "\{CUBE\}.created_at"

  # Child cube extends base
  - name: page_views
    extends: base_events
    sql_table: page_view_events

    dimensions:
      - name: page_url
        type: string
        sql: "\{CUBE\}.url"

  # Another child cube
  - name: purchases
    extends: base_events
    sql_table: purchase_events

    measures:
      - name: total_revenue
        type: sum
        sql: "\{CUBE\}.amount"

How It Works

When a cube extends another:

Measures merge — child gets all parent measures plus its own
Dimensions merge — child gets all parent dimensions plus its own
Segments merge — child gets all parent segments plus its own
Joins merge — child gets all parent joins plus its own

Important: Use {CUBE}

Always use \{CUBE\} when referencing columns in extendable cubes:

# Good - works in parent and child cubes
dimensions:
  - name: created_at
    type: time
    sql: "\{CUBE\}.created_at"

# Bad - breaks in child cubes
dimensions:
  - name: created_at
    type: time
    sql: "\{base_events\}.created_at"

Overriding Members

Child cubes can override parent members by defining them with the same name:

cubes:
  - name: base_orders
    measures:
      - name: count
        type: count
        description: "Total orders"

  - name: completed_orders
    extends: base_orders
    measures:
      - name: count
        type: count
        description: "Completed orders only"
        filters:
          - sql: "\{CUBE\}.status = 'completed'"

Common Patterns

Event Tables

cubes:
  - name: base_event
    dimensions:
      - name: id
        sql: "\{CUBE\}.id"
        primary_key: true
      - name: user_id
        sql: "\{CUBE\}.user_id"
      - name: timestamp
        type: time
        sql: "\{CUBE\}.timestamp"

  - name: clicks
    extends: base_event
    sql_table: click_events

  - name: impressions
    extends: base_event
    sql_table: impression_events

Multi-Tenant Tables

cubes:
  - name: base_orders
    sql: "SELECT * FROM orders WHERE tenant_id = '\{\{COMPILE_CONTEXT.tenant\}\}'"

  - name: tenant_orders
    extends: base_orders

Best Practices

Use {CUBE} everywhere — never hardcode cube names in SQL
Keep base cubes focused — only include truly shared members
Don't over-extend — deep inheritance chains are hard to maintain
Document inheritance — make it clear which cubes extend others