If item not in the store, dispatch an action to fetch it

Question

I'm trying to figure out what is the best way to fetch an item if it's not in the store.

For instance, let say that I have a list of users and I want to fetch a specific user. If that user isn't in the store I want to fetch him from the DB.

Is this code below considered best practice or is there a better way doing so?

const searchedUserId = 'abcdefg'; 
this.selecedUser$ = this.store.select(state => {
   const selectedUserIndex = state.userList.findIndex(searchedUserId)
   if (selectedUserIndex === -1) {
     this.store.dispatch(new UsersActions.FetchUsers(searchedUserId));  
   } else {
     return state.userList[selectedUserIndex]
   }
})

Answer 1

const searchedUserId = 'abcdefg';
this.selecedUser$ = this.store.select('userList').pipe(
  map(userList=>{const result = userList.findIndex(item=>item.id===searchedUserId);
  return result === -1 ? {} : result;
  }),
  tap(userList=>{
    if( !userList.hasOwnProperty('id') ) this.store.dispatch(new UsersActions.FetchUsers(searchedUserId));
  })
);

tap will not change the observable and when the dispatched action will change the state, the observable will be updated.

Use an selector instead of the select statement and be aware about the situation the action will not found the key.