从AngularFireList获取物品的问题

Question

当我尝试通过AngularFireList中的对象之一寻找对象时，无法获得对象（贷款）。你有什么建议？

组件但是，它没有给我任何回报。

 this.prestamoService.obtenerPrestamo("P34520181127")
    .snapshotChanges()
       .subscribe(item => {
         this.prestamoLista = [];
         item.forEach(element =>{
           let x = element.payload.toJSON();
           x["$key"]  = element.key;
           this.prestamoLista.push(x as Prestamo);
         });
       });

服务

import { Injectable } from '@angular/core';

import { AngularFireDatabase, AngularFireList } from 'angularfire2/database';

import { Prestamo } from '../models/prestamo';
import { FirebaseDatabase } from 'angularfire2';

@Injectable({
  providedIn: 'root'
})
export class PrestamoService {

  prestamoLista: AngularFireList<any>;
  prestamoSeleccionado: Prestamo = new Prestamo();

  constructor(private firebase: AngularFireDatabase) {}

  obtenerPrestamo(codigo: string)
  {
    return this.prestamoLista = this.firebase.list('prestamos', ref =>ref.orderByChild('codigo').equalTo(codigo));
  }
}

我需要从我的'obtenerPrestamo（）'方法获得一笔特定的贷款，该方法应该搜索贷款属性。