Angular 8：尝试捕获构造函数，但不返回Value

Question

我正在尝试从Angular 8服务中调用构造函数；

我以前做过这个CRUD操作，但是这次无法正常工作，我找不到原因。

这一次我很头疼，但是我不知道该怎么办。

请感谢由谁来帮助解决此问题。

构造函数对象

export class Book {
  constructor(
    _id = "",
    title = "",
    author = "",
    genre = "",
    details: any,
    status: any,
    current: any
  ) {
    this._id = _id;
    this.title = title;
    this.author = author;
    this.genre = genre;
    this.details = details;
    this.status = status;
    this.current = current;
  }
  _id: string;
  title: string;
  author: string;
  genre: string;
  details: {
    publisher: string;
    year: string;
    isbn: number;
    categories: string;
    language: string;
    pages: number;
  };
  status: {
    loan: boolean;
    sold: boolean;
    lost: boolean;
    donated: boolean;
  };
  current: {
    owner: string;
    location: string;
    edition: string;
  };

角度服务

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

@Injectable({
  providedIn: 'root'
})

export class BookserviceService {
  selectedBook: Book;
  Book: Book[];

  readonly URL_API = `http://localhost:9000/`;

  constructor(private http: HttpClient) {

**ERROR LINE***
    this.selectedBook = new Book(); <-- (Expected 7 arguments, but got 0.ts(2554) bookmodel.ts(3, 5): An argument for '_id' was not provided.)

  }
  postBook(book: Book) {
    return this.http.post(this.URL_API, book);
  }
  getBook() {
    return this.http.get(this.URL_API);
  }
  putBook(book: Book) {
    return this.http.put(this.URL_API + `/${book._id}`, book);
  }
  deleteBook(_id: string) {
    return this.http.delete(this.URL_API + `/${_id}`);
  }
  searchBook(queryString: string) {
    const  baseURL = this.URL_API + queryString;
    return this.http.get(baseURL);

  }
}