SAP CDS view里如何定义association

consumption view里，
@ObjectModel.association.type: [#TO_COMPOSITION_CHILD]
Z_i_Order_View._Item,
@ObjectModel.association.type: [#TO_COMPOSITION_CHILD]
Z_i_Order_View._statushelp
Z_i_Order_View里：
@ObjectModel.association.type: [#TO_COMPOSITION_CHILD]
Z_C_Order_Item._Item,
@ObjectModel.association.type: [#TO_COMPOSITION_CHILD]
_sys_status._statushelp
_sys_status来自：
inner join Zorder_Sys_Status as _sys_status
zorder_sys_status里：
association [0…1] to Z_C_Status_Valuehelp as _statushelp
on $projection.stat = _statushelp.status_key
在view里的定义：
key crmd_orderadm_h.guid,
//@ObjectModel: { foreignKey.association: ‘_statushelp’, mandatory: true }
key _crm_jest.stat,
_status_text.txt04,
_status_text.txt30,
@ObjectModel.association.type: #TO_COMPOSITION_CHILD
_statushelp