Fix mixed-grain measures in Cube order_details view

[samjewell]

The Cube schema currently exposes orders- and customers-grain measures in the order_details view while also traversing the orders -> payments one_to_many join.

That means queries against order_details can return inflated parent-grain measures whenever any payments_* field is included, because orders with multiple payment rows get counted multiple times.

Examples from the current schema:

• orders.count
• orders.gift_count
• orders.avg_priority
• customers.count
• customers.active_count

Why this is a problem:

• order_details includes orders.payments in the same view as those order/customer measures.
• Some orders have multiple payments, so the view becomes payment-grain as soon as a payments field participates in the query.
• That makes the parent-grain measures payment-weighted rather than order- or customer-weighted.

Affected files:

• dev-environment/cube/model/views/order_details.yml
• dev-environment/cube/model/cubes/orders.yml
• dev-environment/cube/model/cubes/customers.yml

Suggested fix:

• Either remove the parent-grain measures from order_details, or
• redefine them in a way that is safe across the one_to_many join for the intended view grain.

Note:

• These same cube/view definitions are also being reused in grafana-play for the play.grafana Cube demo setup, so once fixed here they should be updated there as well.

[samjewell]

A few minor housekeeping items noticed while reviewing the grafana-play PR (#566) that provisioned these model files. Not related to the mixed-grain fix, but worth tidying up in the same pass:

1. Remove pre-aggregation boilerplate comments — All three cubes (customers.yml, orders.yml, payments.yml) carry the scaffolded # Pre-aggregation definitions go here / # Learn more... placeholder. These aren't going to be used in this test dataset and add noise.

2. Remove joins: [] from customers.yml — payments.yml omits the key entirely when there are no joins. Pick one convention; omitting is more idiomatic.

3. Remove the scaffolding comment block from order_details.yml — Lines 1–11 are generic Cube boilerplate referencing a "customers' city dimension" that doesn't exist in this model. Removing it avoids confusion.