Mongodb load collection by ID

Question

Probably something very simple here. I have 2 mongoDb collections, one (users) with an objectId and the other (listings) which has the userId.

I want to get the documents in the listing collection by searching the objectId (currentUser._id).

How would i do this?

Component for page i want to display the listings on:

export class ManageComponent implements OnInit {
    listing : Listing;
    listings: Listing[] = [];
currentUser: User;

constructor(
    private listingService: ListingService,
    private userService: UserService) {
        this.currentUser = JSON.parse(localStorage.getItem('currentUser'));
     }  

ngOnInit() {
    this.loadAllListings();
} 

private loadAllListings() {
    this.listingService.getAll().subscribe(listings => { this.listings = listings; });
}


private loadById(userId: string) {
    this.listingService.getById(userId).subscribe(listings => { this.listings = listings});
    }
}

I have a listing service that is used to for the CRUD operations (some omitted)

import { Injectable } from '@angular/core';
import { Http, Headers, RequestOptions, Response } from '@angular/http';

import { Listing } from '../_models/index';

@Injectable()
export class ListingService {

constructor(private http: Http) { }

getAll() {
    return this.http.get('/listings').map((response: Response) => response.json());
}

getById(_id: string) {
    return this.http.get('/listings/' + _id).map((response: Response) => response.json());
}

getByUserId(userId: string) {
    return this.http.get('/listings/' + userId).map((response: Response) => response.json());
}

create(listing: Listing) {
    return this.http.post('/listings/add', listing);
}

Server side listing controller which uses the server side service (see below):

function getRelevant(req, res) {
listingService.getByUserId(req.listing.sub)
    .then(function (listing) {
        if (listing) {
            res.send(listing);
        } else {
            res.sendStatus(404);
        }
    })
    .catch(function (err) {
        res.status(400).send(err);
    });
}

Server side listing service:

function getByUserId(userId) {
var deferred = Q.defer();

db.listings.findById(userId, function (err, listing) {
    if (err) deferred.reject(err.name + ': ' + err.message);

    if (listing) {
        // return listing 
        deferred.resolve(listing);
    } else {
        // listing not found
        deferred.resolve();
    }
});

return deferred.promise;
}

Answer 1

db.listings.aggregate（[$ lookup：{from：“ users”，localField：“ currentUser._id”，foreignField：“ _id”，as：“ result”}}]））。findOne（{搜索}）

Answer 2

MongoDB's function findById() will find the current model's documents by Id on which the function is operated ( db.listings.findById() will find All Listings by Listing Id).

That said, if you want to find by other criteria that is in your model ( listing ). You need to do find({query}) .

Specifically in your case, you'll need to:

const query = {userId: userIdThatIsPassedIn};
db.listings.find(query).exec(callback);