Brings up typed characteristic values from instances this one has assigned to — the reverse of inheritance.

InheritedCharacteristic is the conventional direction: the assignee inherits its characteristic from its assigner (you inherit from your parents). This is the reverse: the assigner brings up the characteristic of every assignee it's connected to (insanity is hereditary — you get it from your kids).

Traverses OUTGOING AssignmentRelationship records (this instance as source) optionally filtered by alias, then reads the typed characteristic on each assignee.

Useful when the assigner wants to compose its assignees into its own view — e.g. a shelf bringing up the cards it has assigned slots to, ordered by slot number.

Worth yarning upstream alongside inherited_characteristic as a pair of diffo-side DSL declarations.

Options

• characteristic_module: (required) — the typed characteristic Ash resource on each assignee (e.g. CardCharacteristic).
• alias: (optional) — filter outgoing assignments by alias (the assignee's slot name). Use when every consumer follows the same aliasing convention.
• thing: (optional) — filter outgoing assignments by thing (the pool's thing name, e.g. :slot, :port). Always set from the pool DSL declaration, so this is more robust than alias: when consumers don't reliably name their slots. See [[assignment-direction-asymmetry]].

Specify either alias: or thing: (or both); omitting both includes every outgoing assignment from this instance.

Examples

# Shelf brings up the card characteristic from every card it's
# assigned a slot to, ordered by slot number. Cards-as-assignees
# name their slot :slot when requesting.
calculate :cards, {:array, :map},
          {DiffoExample.Calculations.ReverseInheritedCharacteristic,
           [alias: :slot, characteristic_module: CardCharacteristic]}

# NTD brings up the UNI characteristic from every UNI it's assigned
# a port to. The UNIs may not have set an alias on their request,
# so filter by `thing` from the :ports pool declaration.
calculate :unis, {:array, :map},
          {DiffoExample.Calculations.ReverseInheritedCharacteristic,
           [thing: :port, characteristic_module: UniCharacteristic]}