如何根据where子句使用Filter Firebase数据

Question

import { PostService } from './../../../components/services/post.service';
import { PostsDB } from './../../../components/model/posts';
import { NotificationService } from './../../../components/services/toastr.service';
import { Component, OnInit } from '@angular/core';


@Component({
  selector: 'app-articles',
  templateUrl: './articles.component.html',
  styleUrls: ['./articles.component.css']
})
export class ArticlesComponent implements OnInit {

  articleList: PostsDB[];
  
	constructor(private postService: PostService,
    private toastService: NotificationService,//for notifications
  ) { }

  ngOnInit() {
    this.getAllPosts();
  }

  getAllPosts() {
    const x = this.postService.getPosts();
    x.snapshotChanges().subscribe(
      (posts) => {
        this.articleList = [];
        posts.forEach((element) => {
          const y = element.payload.toJSON();
          y['$key'] = element.key;
          this.articleList.push(y as PostsDB);
        });
      },
      (err) => {
        this.toastService.showSuccess("Error", "error occurred");      }
    );
  }
}

我正在Angular Firebase Realtime DB中构建具有多个帖子类型的博客应用。我只想像我们在SQL中那样实现Firebase查询，例如SELECT * FROM POSTTABLE WHERE POSTCATEGORY ='ARTICLE'。 如何在Firebase Realtime数据库中实现此类查询。

这是我的Component.ts代码，从Firebase数据库中获取所有帖子：- Appcomponent.component.ts