docs: show the multi-fact AOV measure owned by a cube, not only by a view

docs-mintlify/docs/data-modeling/views.mdx

@@ -285,11 +285,10 @@ straightforward.
 
 ### Define a metric on a view when it spans cubes
 
-The one exception is a metric whose parts live in different cubes, so there is
-no single cube it could belong to. A view can define its own
-[measures][ref-view-measures] and [dimensions][ref-view-dimensions] as long as
-their `sql` only combines members the view already includes — a member that
-reads a column instead is rejected at compile time:
+The exception is a metric whose parts live in different cubes. A view can define
+its own [measures][ref-view-measures] and [dimensions][ref-view-dimensions] as
+long as their `sql` only combines members the view already includes — a member
+that reads a column instead is rejected at compile time:
 
 <CodeGroup>
 
@@ -328,6 +327,11 @@ inflate the numerator. If the cubes don't join to each other at all, see
 [multi-fact views][ref-multi-fact-views]. The full example, with the `cubes`
 block, is on the [view reference][ref-view-measures].
 
+A cube can also own such a metric, by referencing the other cube's member
+directly — that keeps it defined once for every view that includes it, at the
+cost of one cube naming another. The [average order value
+recipe][ref-recipe-aov] compares the two placements.
+
 ### Control visibility
 
 Not every view should be publicly accessible. Use [`public`][ref-view-public]
@@ -499,6 +503,7 @@ parameters.
 [ref-view-dimensions]: /reference/data-modeling/view#dimensions
 [ref-multi-stage]: /reference/data-modeling/measures#multi_stage
 [ref-multi-fact-views]: /docs/data-modeling/multi-fact-views
+[ref-recipe-aov]: /recipes/data-modeling/average-order-value#where-to-put-the-measure
 [ref-view-folders]: /reference/data-modeling/view#folders
 [ref-access-policies]: /reference/data-modeling/data-access-policies
 [ref-ai-context]: /docs/data-modeling/ai-context

docs-mintlify/recipes/data-modeling/average-order-value.mdx

@@ -230,9 +230,9 @@ since one is keyed by day and the other by timestamp.
 
 ### 2. Define AOV on the view
 
-Neither cube can define AOV — neither can reference the other's measures. Define
-it as a [measure of the view][ref-view-measures] and mark it
-[`multi_stage`][ref-multi-stage]:
+AOV can live on the view or on either cube — see [where to put
+it](#where-to-put-the-measure) below. On the view it is a [measure of the
+view][ref-view-measures], marked [`multi_stage`][ref-multi-stage]:
 
 <CodeGroup>
 
@@ -331,8 +331,83 @@ measure, looks for a single join tree covering both fact cubes, and fails with
 
 </Note>
 
+## Where to put the measure
+
+A metric spanning two facts does not have to live on a view. A cube measure may
+reference another cube's measure, which makes it derived rather than owned by
+its cube — the same property a view measure has — so AOV can sit on either fact
+cube instead:
+
+<CodeGroup>
+
+```yaml title="YAML"
+cubes:
+  - name: sales_line_item
+    # …
+
+    measures:
+      - name: transactions_without_returns
+        sql: transaction_id
+        type: count_distinct
+        filters:
+          - sql: "{CUBE}.transaction_type <> 'EXCHANGE'"
+          - sql: "{CUBE}.fulfillment_channel_group IN ('IN_STORE', 'SHIP_FROM_STORE')"
+
+      - name: aov_basket
+        type: number
+        format: currency
+        multi_stage: true
+        sql: "{item_location_sales.sales_amount} / NULLIF({CUBE.transactions_without_returns}, 0)"
+```
+
+```javascript title="JavaScript"
+cube(`sales_line_item`, {
+  // …
+
+  measures: {
+    transactions_without_returns: {
+      sql: `transaction_id`,
+      type: `count_distinct`,
+      filters: [
+        { sql: `${CUBE}.transaction_type <> 'EXCHANGE'` },
+        { sql: `${CUBE}.fulfillment_channel_group IN ('IN_STORE', 'SHIP_FROM_STORE')` }
+      ]
+    },
+
+    aov_basket: {
+      type: `number`,
+      format: `currency`,
+      multi_stage: true,
+      sql: `${item_location_sales.sales_amount} / NULLIF(${CUBE.transactions_without_returns}, 0)`
+    }
+  }
+})
+```
+
+</CodeGroup>
+
+Both placements plan identically — the same per-fact subqueries, stitched the
+same way, divided in the same final stage — and `multi_stage` is required either
+way. What differs is reuse and coupling:
+
+| | On a cube | On a view |
+| --- | --- | --- |
+| Reuse | Defined once; every view including it gets it | Redefined in each view that needs it |
+| Coupling | The cube names the other cube's measure | The cubes stay unaware of each other |
+| Query path | Available as `sales_line_item.aov_basket` too | Only through the view |
+
+Prefer the cube when the metric is part of the model that several views expose —
+it keeps [shared logic in cubes][ref-views-shared-logic]. Prefer the view when
+the pairing is a presentation choice for one audience, or when the cubes belong
+to different domains and you would rather not have one reference the other.
+
+A cube-owned measure reaches the other fact whether or not the view naming it
+also includes that fact, so a view can expose AOV without exposing
+`sales_amount`.
+
 [ref-multi-fact-views]: /docs/data-modeling/multi-fact-views
 [ref-multi-stage]: /reference/data-modeling/measures#multi_stage
 [ref-measure-filters]: /reference/data-modeling/measures#filters
 [ref-view-measures]: /reference/data-modeling/view#measures
+[ref-views-shared-logic]: /docs/data-modeling/views#keep-shared-logic-in-cubes
 [link-tesseract]: https://cube.dev/blog/introducing-tesseract

docs-mintlify/reference/data-modeling/view.mdx

@@ -571,7 +571,9 @@ If you'd like to override the [metadata][ref-dim-meta] of a member, you can use
 The `measures` parameter defines measures on the view itself. A view measure is
 always _derived_: its `sql` may only reference members that the view already
 includes, never columns of a table. Use it for a metric whose parts come from
-different cubes, which therefore has no single cube to live in.
+different cubes. (A cube can own such a metric too, by referencing the other
+cube's member; the [average order value recipe][ref-recipe-aov] compares the two
+placements.)
 
 Reference the included members as `{CUBE.member}` (or `{view_name.member}`); a
 bare `{member}` does not resolve inside a view.
@@ -1112,6 +1114,7 @@ The `access_policy` parameter is used to configure [access policies][ref-ref-dap
 [ref-ref-cubes]: /reference/data-modeling/cube
 [ref-ref-multi-stage]: /reference/data-modeling/measures#multi_stage
 [ref-multi-fact-views]: /docs/data-modeling/multi-fact-views
+[ref-recipe-aov]: /recipes/data-modeling/average-order-value#where-to-put-the-measure
 [ref-ref-hierarchies]: /reference/data-modeling/hierarchies
 [ref-ref-dap]: /reference/data-modeling/data-access-policies
 [ref-rest-query-ops]: /reference/core-data-apis/rest-api/query-format#filters-operators

packages/cubejs-schema-compiler/test/unit/multi-fact-derived-measure-in-view.test.ts

@@ -101,6 +101,16 @@ cubes:
         filters:
           - sql: "{CUBE}.transaction_type <> 'EXCHANGE'"
           - sql: "{CUBE}.fulfillment_channel_group IN ('IN_STORE', 'SHIP_FROM_STORE')"
+      # The same ratio, owned by this cube instead of the view. Referencing the
+      # other fact's measure is what makes it not owned by this cube, which is
+      # what a derived member has to be; the \`multi_stage\` rule is unchanged.
+      - name: aov_basket
+        type: number
+        multi_stage: true
+        sql: "{item_location_sales.sales_amount} / NULLIF({CUBE.transactions_without_returns}, 0)"
+      - name: aov_basket_single_stage
+        type: number
+        sql: "{item_location_sales.sales_amount} / NULLIF({CUBE.transactions_without_returns}, 0)"
 
   - name: item_location_sales
     sql: >
@@ -139,6 +149,8 @@ views:
         includes:
           - transactions_without_returns
           - net_sale_transactions
+          - name: aov_basket
+            alias: aov_basket_from_cube
       # The shared dimension cubes sit at root-level join paths so their
       # dimensions are common to both facts.
       - join_path: dates
@@ -326,6 +338,86 @@ describe('Multi-fact derived measure defined on a view', () => {
   });
 });
 
+// The same ratio, owned by `sales_line_item` rather than by the view. A cube
+// measure that references another cube's measure is not owned by its cube -
+// the same property a view measure has - so a metric spanning two facts does
+// not need a view to live in. It can sit in the model, and every view that
+// includes it gets it.
+describe('Multi-fact derived measure defined on a cube', () => {
+  it('divides the two facts once both have been aggregated to the query grain', () => {
+    const sql = buildSql({
+      measures: ['sales_line_item.aov_basket'],
+      dimensions: ['locations.region'],
+    });
+
+    expect(sql).toMatch(SALES_AMOUNT_AGGREGATE);
+    expect(sql).toMatch(TRANSACTIONS_AGGREGATE);
+    expect(sql).toMatch(RATIO_OVER_AGGREGATES);
+    expect(sql).not.toMatch(/sum\("item_location_sales"\.sales_amount\) \/ NULLIF/);
+  });
+
+  it('plans the same way whichever fact owns it', () => {
+    // Only the emitted column alias should differ between the two placements,
+    // so normalising it makes the two plans directly comparable.
+    const normalize = (sql: string) => sql
+      .replace(/"(retail_analysis|sales_line_item)__aov_basket"/g, '"__aov"')
+      .replace(/"retail_analysis__region"/g, '"__region"')
+      .replace(/"locations__region"/g, '"__region"');
+
+    const onView = buildSql({
+      measures: ['retail_analysis.aov_basket'],
+      dimensions: ['retail_analysis.region'],
+    });
+    const onCube = buildSql({
+      measures: ['sales_line_item.aov_basket'],
+      dimensions: ['locations.region'],
+    });
+
+    expect(normalize(onCube)).toEqual(normalize(onView));
+  });
+
+  it('is reachable through a view that includes it', () => {
+    const sql = buildSql({
+      measures: ['retail_analysis.aov_basket_from_cube'],
+      dimensions: ['retail_analysis.region'],
+    });
+
+    expect(sql).toMatch(RATIO_OVER_AGGREGATES);
+  });
+
+  it('reaches the other fact even when the query names only its own cube', () => {
+    const sql = buildSql({ measures: ['sales_line_item.aov_basket'] });
+
+    // No dimensions, so the two legs are aggregated whole and stitched anyway.
+    expect(sql).toMatch(SALES_AMOUNT_AGGREGATE);
+    expect(sql).toMatch(TRANSACTIONS_AGGREGATE);
+    expect(sql).toMatch(RATIO_OVER_AGGREGATES);
+  });
+
+  it('divides the two facts on the shared date spine', () => {
+    const sql = buildSql({
+      measures: ['sales_line_item.aov_basket'],
+      timeDimensions: [{ dimension: 'dates.date', granularity: 'day' }],
+    });
+
+    expect(sql).toContain('DATE_TRUNC(\'day\', "item_location_sales".date) = "dates".date');
+    expect(sql).toContain('DATE_TRUNC(\'day\', "sales_line_item".sold_at) = "dates".date');
+    expect(sql).toMatch(RATIO_OVER_AGGREGATES);
+  });
+
+  // Current behaviour, pinned - the same limit as on the view. Owning the
+  // measure buys the cube nothing here: without `multi_stage` the planner still
+  // looks for one join tree covering both facts and there is none.
+  it('cannot plan the ratio when the cube measure is not multi_stage', () => {
+    // The cubes are listed in the order the planner collected them, which
+    // differs from the view-owned case, so only their presence is pinned.
+    expect(() => buildSql({
+      measures: ['sales_line_item.aov_basket_single_stage'],
+      dimensions: ['locations.region'],
+    })).toThrow(/Can't find join path to join (?=.*item_location_sales)(?=.*sales_line_item)/);
+  });
+});
+
 // The other reason a view measure spanning cubes wants `multi_stage`: even when
 // the cubes DO join, a plain calculated measure is evaluated inside the single
 // joined scan, so a `sum` on the one side is taken over rows the join has