Question

我正在尝试通过ID从实体状态中选择一个对象。下面是我的减速器。

 export interface MessageState extends EntityState<Message> {
  // additional entities state properties
  loaded: boolean;
  loading: boolean;
}

export const adapter: EntityAdapter<Message> = createEntityAdapter<Message>({
  selectId: (msg: Message) => msg.messageId,
});

export const initialState: MessageState = adapter.getInitialState({
  // additional entity state properties
  loaded: false,
  loading: false,
});

export function reducer(state = initialState, action: MessageActionsUnion): MessageState {
  switch (action.type) {

    case MessageActionTypes.UPSERT_Message: {
      return { ...state, loading: true, loaded: false };
    }

    case MessageActionTypes.UPSERT_Message_SUCCESS: {
      return adapter.upsertOne(action.payload.Message,
        {
          ...state, loaded: true, loading: false,
        });

    }

    default: {
      return state;
    }
  }
}

下面是我的index.ts文件

export interface State extends fromRoot.AppState {
  queueModule: QueueState;
}

export interface QueueState {
  msgHeaders: fromMsgHeaders.MessageHeaderState
}

export const reducers: ActionReducerMap<QueueState> = {
  msgHeaders: fromMsgHeaders.reducer

};

export const getQueueState$ = createFeatureSelector<QueueState>('queueModule');

我试图在传递ID时形成选择器，该ID将从实体返回值。

    export const selectMessages = createSelector(
      fromFeatures.getQueueState$,
      (state: fromFeatures.QueueState) => state.msgs
    );

    export const {
      selectAll: selectAllMessages,
      selectEntities: selectMessagesEntities,
      selectIds: selectMessagesIds,
      selectTotal: selectMessagesTotal
    } = adapter.getSelectors(selectMessages);

我看了很多资源，但是不清楚如何通过传递ID选择对象。

Answer 1

sat p = for c from item: -- do { c <- item if p c -- ; if p c then return c -- then return c else failParse -- else failParse }没有提供@ngrx/entity选择器。

在大多数情况下，这是您不需要做的事情。

话虽这么说，但有多种方法可以创建一个选择器来做到这一点，有关更多信息，请参见（NgRx：参数化选择器）[https://blog.angularindepth.com/ngrx-parameterized-selector-e3f610529f8]。

例如：

getOneById

Answer 2

@ngrx/entity在发布了dictionary的v6.1.0（ngrx entity changelog）版本之后确实提供了getEntityValueById。

因此，我可以按以下方式通过其ID提取实体的单个值。

// in the selector
import { Dictionary} from '@ngrx/entity;

export const getMessageById = () => {
  return createSelector(
    selectMessagesEntities,                
    (entities: Dictionary<Message>, props: { messageId: number }) => {
      return entities[props.messageId];
    },
  );
};


//to call the selector


this.msg$ = this.store.pipe(select(
      fromStore.getMessageById(), { messageId: 10 }
    )).pipe(
      map(
        (message: Message) => {
          return this.msg = message;
        },
      )
    );

此方法也有很好的参考文献 here。

角度NGRX：无法基于id在ngrx实体中选择单个值

2 个答案: