从reactjs redux中的mongodb获取集合长度

我想在react with redux中显示mongodb中的集合长度

这是我的密码：

行动：

carActions.js

export const howMany = () => async (dispatch) => {
try {
    dispatch({ type: CAR_NUMBER_REQUEST })

    const { data } = await axios.get('/api/cars')

    dispatch({ type: CAR_NUMBER_SUCCESS, data })
} catch (error) {
    dispatch({
        type: CAR_NUMBER_FAIL, payload: error.message})
}

export const carNumberReducer = (state = { cars: [] }, action) => {
switch (action.type) {
    case CAR_NUMBER_REQUEST:
        return { loading: true, cars: [] }
    case CAR_NUMBER_SUCCESS:
        return { loading: false, success: true, cars: action.payload }
    case CAR_NUMBER_FAIL:
        return { loading: false, error: action.payload }
    default:
        return state
}

const dispatch = useDispatch()

const carNumber = useSelector(state => state.carNumber)
const { cars } = carNumber
useEffect(() => {
    dispatch(howMany());
}, [dispatch])
return (
        <div>
            {cars.map((cars) => (
                <p key={cars._id}>{cars}</p>
            ))}
        </div>)}

}

减速器：

carReducer.js

export const howMany = () => async (dispatch) => {
try {
    dispatch({ type: CAR_NUMBER_REQUEST })

    const { data } = await axios.get('/api/cars')

    dispatch({ type: CAR_NUMBER_SUCCESS, data })
} catch (error) {
    dispatch({
        type: CAR_NUMBER_FAIL, payload: error.message})
}

export const carNumberReducer = (state = { cars: [] }, action) => {
switch (action.type) {
    case CAR_NUMBER_REQUEST:
        return { loading: true, cars: [] }
    case CAR_NUMBER_SUCCESS:
        return { loading: false, success: true, cars: action.payload }
    case CAR_NUMBER_FAIL:
        return { loading: false, error: action.payload }
    default:
        return state
}

const dispatch = useDispatch()

const carNumber = useSelector(state => state.carNumber)
const { cars } = carNumber
useEffect(() => {
    dispatch(howMany());
}, [dispatch])
return (
        <div>
            {cars.map((cars) => (
                <p key={cars._id}>{cars}</p>
            ))}
        </div>)}

}

将在此处显示：

carScreen.js

export const howMany = () => async (dispatch) => {
try {
    dispatch({ type: CAR_NUMBER_REQUEST })

    const { data } = await axios.get('/api/cars')

    dispatch({ type: CAR_NUMBER_SUCCESS, data })
} catch (error) {
    dispatch({
        type: CAR_NUMBER_FAIL, payload: error.message})
}

export const carNumberReducer = (state = { cars: [] }, action) => {
switch (action.type) {
    case CAR_NUMBER_REQUEST:
        return { loading: true, cars: [] }
    case CAR_NUMBER_SUCCESS:
        return { loading: false, success: true, cars: action.payload }
    case CAR_NUMBER_FAIL:
        return { loading: false, error: action.payload }
    default:
        return state
}

const dispatch = useDispatch()

const carNumber = useSelector(state => state.carNumber)
const { cars } = carNumber
useEffect(() => {
    dispatch(howMany());
}, [dispatch])
return (
        <div>
            {cars.map((cars) => (
                <p key={cars._id}>{cars}</p>
            ))}
        </div>)}

const dispatch=usedpatch（）
常量carNumber=useSelector（state=>state.carNumber）
常数{cars}=carNumber
useffect（（）=>{
分派（多少个（））；
}[快讯]）
返回(
{cars.map（（cars）=>(
{cars}
))}
)}

哪里有错误？我已经用一个图片更新了这篇文章，如果你能看到它的话，你会大摇大摆吗？您能测试Api返回的集合是否正确吗？我在postman上测试了它，它正常工作。您是否配置了CORS？