Children and parents

An include: section adds related records to the result, each under a field of the result type. This board shows a project with its owner and its open todos:

// domains/planning/queries/project_board.jadpoquery project_board(project_id: Project.id) fails BoardNotFound -> ProjectBoardView {    from: Project    where: Project.id == project_id    missing: BoardNotFound    include: {        owner: Project.owner_id        todos: {            via: Todo.project_id            where: Todo.status == TodoStatus.open            order: [Todo.created_at asc]            limit: 50        }    }}type ProjectBoardView = Output {    pick: [Project.id, Project.name]    owner: UserView    todos: List<TodoView>}

Naming one of this entity's own references (Project.owner_id) includes the record it points to, its parent. Naming another entity's reference to this one (Todo.project_id) includes the records that point here, its children. Children are a list, which needs order: and limit: in a block, or at most one record when that reference is unique. A parent never declares its children (Children).

Each include costs one more database query, however many records the result holds, never one per record. A parent or a unique child is read by = ANY of the keys the records hold. A list is read through a LATERAL subquery that orders and limits each record's list on its own.

Includes nest up to two levels and stay inside the domain. They reach another store only to fetch records by id. A parent is included even when its lifecycle hides it, because the reference still holds.