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[英]Error deploying MERN application to Heroku (Front-end deployed successfully, but the back-end didn't)
[英]React front end not updating after delete operation in MERN application
我有一个 MERN 应用程序,当单击删除按钮时,我试图删除一个注释(由标题和内容组成)。 当我单击该按钮时,后端 mongoDB 数据库被更新 - 该项目实际上已被删除 - 但随后控制台会发出错误消息。
这是删除操作,通过相关文件进行跟踪:
// App.jsx
const deleteNote = id => {
NoteDataService.deleteNote(id)
.then(response => {
console.log(`note ${id} deleted`);
setNotes(prevState => {
return prevState.notes.filter(note => note._id !== id);
});
})
.catch(e => console.log(e));
};
// note.js
import http from '../http-common.js';
class NoteDataService {
createNote = data => http.post('/', data);
getAll = () => http.get('/');
deleteNote = id => http.delete(`?id=${id}`);
}
export default new NoteDataService();
// http-common.js
import http from '../http-common.js';
class NoteDataService {
createNote = data => http.post('/', data);
getAll = () => http.get('/');
deleteNote = id => http.delete(`?id=${id}`);
}
export default new NoteDataService();
这是错误:
App.jsx:41 Uncaught TypeError: Cannot read property 'filter' of undefined
at App.jsx:41
在我尝试实现的 CRUD 操作中,似乎只有“读取”(获取)功能可以正常工作以最初从后端填充我的笔记列表(在 App 组件加载时使用 useEffect())。
这工作...
const deleteNote = id => {
NoteDataService.deleteNote(id)
.then(response => {
console.log(`note ${id} deleted`);
console.log(notes);
setNotes(notes.filter(note => note._id !== id));
})
.catch(e => console.log(e));
};
在组件安装之前,您的状态notes
将为null
。 请检查您所在州的notes
不为null
,它是一个array
就可以了
prevState.notes && prevState.notes.filter(note => note._id !== id)
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