Extending cubes

Cube supports the extends feature, which allows you to reuse all declared members of a cube. This is a foundation for building reusable data models.

Cubes are represented as JavaScript objects (opens in a new tab) with such properties as measures, dimensions, and segments. Extending in Cube works similarly to JavaScript’s prototype inheritance. Measures, dimensions, and segments are merged as separate objects. So if the base cube defines measure a and the extending cube defines measure b, the resulting cube will have both measures a and b.

The usual pattern is to extract common measures, dimensions, and joins into the base cube and then extend from the base cube. This helps to prevent code duplication and makes code easier to maintain and refactor.

In the example below, the base_events cube defines the common events measures, dimensions, and a join to the users cube:

cubes:
  - name: base_events
    sql_table: events
 
    joins:
      - name: users
        relationship: many_to_one
        sql: "{CUBE}.user_id = {users.id}"
 
    measures:
      - name: count
        type: count
 
    dimensions:
      - name: timestamp
        sql: time
        type: time

The product_purchases and page_views cubes are extended from base_events and define only the specific dimensions: product_name for product purchases and page_path for page views.

cubes:
  - name: product_purchases
    sql_table: product_purchases
    extends: base_events
 
    dimensions:
      - name: product_name
        sql: product_name
        type: string
 
  - name: page_views
    sql_table: page_views
    extends: base_events
 
    dimensions:
      - name: page_path
        sql: page_path
        type: string

Usage with FILTER_PARAMS

If the base cube is using FILTER_PARAMS in any sql property, then extending cubes can do one of two things:

• Override the sql property in each target cube.

  YAML

  JavaScript

  cubes:
    - name: product_purchases
      sql: >
        SELECT *
        FROM events
        WHERE {FILTER_PARAMS.product_purchases.timestamp.filter('time')}
   
      # ...

• Put all filters inside the base cube and reference all specific cubes filters using AND. The unused filters will be rendered to 1 = 1 in the SQL query.

  YAML

  JavaScript

  cubes:
    - name: base_events
      sql: >
        SELECT *
        FROM events
        WHERE
          {FILTER_PARAMS.base_events.timestamp.filter('time')} AND
          {FILTER_PARAMS.product_purchases.timestamp.filter('time')} AND
          {FILTER_PARAMS.page_views.timestamp.filter('time')}
   
      # ...