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我正在尝试创建一个简单的选择器来通过 a 获取商店中的所有消息visitor_id，但是，看起来如此简单的事情在 ngrx 中实现总是具有挑战性。

我正在使用ngrx实体，所以我已经selectAll准备好选择器，所以我尝试执行以下操作：

export const selectMessagesState = createFeatureSelector<MessagesState>('messages');

export const selectAllMessages =  createSelector(
    selectMessagesState,
    fromMessage.selectAll
);

export const selectMessageByVisitorId = createSelector(
    select(selectAll),
    (visitor_id) => map(val => val.filter(c => c.visitor_id == visitor_id))
);

在组件中：

export class Message {
    id: number;
    message: string;
    visitor_id: number;
    is_from_visitor: boolean;
    created_at: string;
}
public messages$ : Observable<Message[]>;

public showThread(visitor: Visitor){

   this.messages$ = this.store.select(selectMessageByVisitorId({ visitor_id: visitor.id}));

不过我要Property 'filter' does not exist on type 'unknown'进去了selectMessageByVisitorId。我很确定我没有遵循正确的方法。我要做的很简单，将 a 传递visitor id给选择selectMessageByVisitorId器，它会返回特征存储中的消息列表，由visitor_id.

更新#1

根据@Nikhil 的建议，我将选择器更改为：

export const selectMessageByVisitorId = ({visitor_id}) => createSelector(
    select(selectAll),
    messages => messages.filter(val => val.visitor_id == visitor_id)
);

但是我得到了Property 'filter' does not exist on type 'Observable<Message[]>，虽然我导入了事件import { filter} from 'rxjs/operators';（我使用 ngrx 8.0）。

所以我想尝试：

export const selectMessageByVisitorId = ({visitor_id}) => createSelector(
    select(selectAll),
    messages => messages.pipe(
            map(val => val.filter(c => c.visitor_id == visitor_id)  ) 
        )
);

但现在我进入Type 'Observable<Observable<Message[]>>' is not assignable to type 'Observable<Message[]>'.了组件文件this.messages$ = this.store.select(selectMessageByVisitorId({ visitor_id: visitor.id}));

4

1 回答 1

2

map()这里不需要，只需使用filter().

方法一：

export const selectMessageByVisitorId = ({visitor_id}) => createSelector(   
    pipe(
     select(selectAll),
     filter(val => val.visitor_id == visitor_id)
    )
);

方法二：

export const selectAllMessages =  createSelector(
    selectMessagesState,
    fromMessage.selectAll
);

export const selectMessageByVisitorId = ({visitor_id}) => createSelector(
    selectAllMessages,
    messages => messages.filter(val => val.visitor_id == visitor_id)
);

然后订阅消息。

this.messages$ = this.store.select(
  selectMessageByVisitorId({visitor_id: visitor.id})
);

this.messages$.subscribe((messages) => {
  // Handle response.
  console.log(messages);
});
于 2019-09-28T18:27:12.627 回答