# `Diffo.Provider.Calculations.FieldFromAssignment`
[🔗](https://github.com/diffo-dev/diffo/blob/v0.9.0/lib/diffo/provider/components/calculations/field_from_assignment.ex#L5)

Reads a field directly from an `AssignmentRelationship` record.

Filters `AssignmentRelationship` by `target_id = current.id` and returns the named
field from each matching record — no second hop to the source instance. This is the
right choice when you want a value that lives on the relationship itself (`:value`,
`:thing`, `:pool`, `:alias`) rather than on the assigning instance.

Use `FieldViaAssignedRelationship` instead when you need a field from the source
instance (e.g. `:name`).

## Options

- `field:` *(required)* — atom naming the field to read from the relationship record
  (e.g. `:value`, `:thing`, `:pool`, `:alias`).
- `alias:` *(optional)* — atom matching the `alias` attribute on the relationship.
  When omitted, all assignments where `target_id = current.id` are included.

## Examples

    # Port number assigned to this service under the :primary slot
    calculate :assigned_port, {:array, :integer},
      {Diffo.Provider.Calculations.FieldFromAssignment, [alias: :primary, field: :value]}

    # Pool name for every assignment on this instance
    calculate :assignment_pools, {:array, :atom},
      {Diffo.Provider.Calculations.FieldFromAssignment, [field: :pool]}

# `describe`

# `has_calculate?`

# `has_expression?`

# `init`

# `strict_loads?`

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*Consult [api-reference.md](api-reference.md) for complete listing*