“对象”类型上不存在属性“数据”

Question

当我尝试从我的 api 获取数据时，我在我的 angular 6 项目中收到此错误。这是我的 api json 文件；

{"data":
[{"category_name":"Women Ready Made","slug":null,"image_url":"education.jpg","products": 
[{"productName":"Kampala 
Shorts","description":"Beautiful Handwoven Kampala Shorts","imageUrl":"C:\\codes\\Tradsonline\\img\\image1.jpg","price":2500,"discount":10},{"productName":"Flowing White Agbada","description":"Flowing white agbada with beautiful design.","imageUrl":"C:\\codes\\Tradsonline\\img\\image3.jpg","price":22000,"discount":15}]},{"category_name":"Men's Ready Made","slug":null,"image_url":"education.jpg","products":[{"productName":"Ankara Jacket","description":"Ankara Jackets with pockets.","imageUrl":"C:\\codes\\Tradsonline\\img\\image2.jpg","price":5000,"discount":15},{"productName":"Women Ankara Gown","description":"Women Ankara gown with beautiful design.","imageUrl":"C:\\codes\\Tradsonline\\img\\image4.jpg","price":8000,"discount":0}]},{"category_name":"Ankara Gowns","slug":null,"image_url":"education.jpg","products":[]}]}

这是我的服务

getCategories(): Observable<Category[]> {
  return this.http.get(this.base_url + 'categories')
    .pipe(map(res => {
       return res.data; //this is where the error happens
}));

这是我对我的服务的进口

import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';

import { Product } from '../models/product';
import { Category } from '../models/category';

import { Observable } from 'rxjs';
import { map } from 'rxjs/operators';

错误从何而来？

Answer 1

如果您没有为http.getcall指定泛型类型参数，则object假定为传入的类型map。object没有名为data（您正在调用）的属性，因此会出现编译时间错误。

更改它，以便您在对 的调用中在泛型类型约束中定义返回的结构http.get<T>。

getCategories(): Observable<Category[]> {
    return this.http.get<{data: Category[]}>(this.base_url + 'categories')
        .pipe(map(res => {
          return res.data; // now .data is known and is expected to contain Category[]
        }));
}