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Rest with Express.js nested router

Suppose I want to have REST endpoints which look roughly like this:

/user/
/user/user_id 

/user/user_id/items/
/user/user_id/items/item_id

CRUD on each if makes sense. For example, /user POST creates a new user, GET fetches all users. /user/user_id GET fetches just that one user.

Items are user specific so I put them under user_id, which is a particular user.

Now to make Express routing modular I made a few router instances. There is a router for user, and a router for the item.

var userRouter = require('express').Router();
userRouter.route('/')
  .get(function() {})
  .post(function() {})
userRouter.route('/:user_id')
  .get(function() {})

var itemRouter = require('express').Router();
itemRouter.route('/')
  .get(function() {})
  .post(function() {})
itemRouter.route('/:item_id')
  .get(function() {})

app.use('/users', userRouter);

// Now how to add the next router?
// app.use('/users/', itemRouter);

URL to item is descendents of the URL hierarchy of the user. Now how do I get URL with /users whatever to userRouter but the more specific route of /user/*user_id*/items/ to the itemRouter? And also, I would like user_id to be accessible to itemRouter as well, if possible.

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Answer

You can nest routers by attaching them as middleware on an other router, with or without params.

You must pass {mergeParams: true} to the child router if you want to access the params from the parent router.

mergeParams was introduced in Express 4.5.0 (Jul 5 2014)

In this example the itemRouter gets attached to the userRouter on the /:userId/items route

This will result in following possible routes:

GET /user -> hello user
GET /user/5 -> hello user 5
GET /user/5/items -> hello items from user 5
GET /user/5/items/6 -> hello item 6 from user 5 

var express = require('express');
var app = express();

var userRouter = express.Router();
// you need to set mergeParams: true on the router,
// if you want to access params from the parent router
var itemRouter = express.Router({mergeParams: true});

// you can nest routers by attaching them as middleware:
userRouter.use('/:userId/items', itemRouter);

userRouter.route('/')
    .get(function (req, res) {
        res.status(200)
            .send('hello users');
    });

userRouter.route('/:userId')
    .get(function (req, res) {
        res.status(200)
            .send('hello user ' + req.params.userId);
    });

itemRouter.route('/')
    .get(function (req, res) {
        res.status(200)
            .send('hello items from user ' + req.params.userId);
    });

itemRouter.route('/:itemId')
    .get(function (req, res) {
        res.status(200)
            .send('hello item ' + req.params.itemId + ' from user ' + req.params.userId);
    });

app.use('/user', userRouter);

app.listen(3003);
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