[英]ReactJS/Javascript/Graphql/React-apollo: Cannot read property 'name' of undefined
GraphQL Query Defined here GraphQL 查询在此处定义
const countryQuery = gql`
query getQuery($filter: _CountryFilter!) {
Country(filter: $filter) {
_id
name
capital
population
nativeName
}
}
`
pages/search.js页面/search.js
export default function Search() {
const [filter, setFilter] = useState({ name: 'Chile' })
const { data, loading, error } = useQuery(countryQuery, {
variables: { filter },})
if (loading){
return <Loader />;
}
if (error) return <p>Error</p>;
return (
<div className="body">
<h1>
Get Information
<br /> about Countries!
</h1>
<div className="wrapper">
<input
className="search"
type="text"
id="search"
placeholder='Enter a Country'
/>
<button
className="submit"
type="submit"
value=" "
onClick={e => setFilter({ name: e.target.value })}
onBlur={e => setFilter({ name: e.target.value })}
> Search
</button>
<div>
{ data?.Country && <CountryInfo country={data?.Country[0]} /> }
</div>
</div>
</div>
);
}
components/queryResults.js This is were I am getting the error. components/queryResults.js这是我得到的错误。 Is {country.name}, {country.capital} etc. the incorrect way to apply the data here?
{country.name}、{country.capital} 等在此处应用数据的方式是否不正确?
import React from 'react'
import { Card, ListGroup, ListGroupItem } from 'react-bootstrap'
const CountryInfo = ({country}) => (
<div>
<Card style={{ width: '18rem' }}>
<Card.Body>
<Card.Title>{country.name}</Card.Title>
</Card.Body>
<ListGroup className="list-group-flush">
<ListGroupItem>Capital: {country.capital} </ListGroupItem> {' '}
<ListGroupItem>Population: {country.population}</ListGroupItem>
<ListGroupItem>Native Name: {country.nativeName}</ListGroupItem>
</ListGroup>
</Card>
</div>
)
export default CountryInfo;
When I type a country and click the search the error is happening on this line: <Card.Title>{country.name}</Card.Title>
Why is name, capital, population and nativeName undefined?当我输入国家并单击搜索时,此行发生错误:
<Card.Title>{country.name}</Card.Title>
为什么名称、首都、人口和 nativeName 未定义? What am I doing wrong?我究竟做错了什么?
I'm looking at this line and would like to note that if data.country is an empty array, it will still be truthy.我正在查看这一行并想指出,如果 data.country 是一个空数组,它仍然是真实的。 Add a check to see if there is a value in the first element of the array before rendering CountryInfo
在渲染 CountryInfo 之前添加检查以查看数组的第一个元素中是否有值
{ data?.Country && <CountryInfo country={data?.Country[0]} /> }
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