diff --git a/app/api/chat.js b/app/api/chat.js
index 04d978a386fe398723a919e81c89905834a0f460..a95a4a368e61f963691d0cb293867ba360fc68c6 100644
--- a/app/api/chat.js
+++ b/app/api/chat.js
@@ -17,7 +17,7 @@ let app = express.Router()
 
 // <root>/chat/<id>/init
 app.post('/:id/init', async function (req, res, next) {
-  let id = Number(req.params.id)
+  let id = req.params.id
   let token = req.body.token
 
   try {
@@ -40,7 +40,7 @@ app.post('/:id/init', async function (req, res, next) {
 
 // <root>/chat/<id>/monitor
 app.post('/:id/monitor', async function (req, res) {
-  let id = Number(req.params.id)
+  let id = req.params.id
 
   await listen.monitorAsync(id, function (resolve) {
     req.connection.on('close', () => resolve())
@@ -53,7 +53,7 @@ app.post('/:id/monitor', async function (req, res) {
 
 // <root>/chat/<id>
 app.post('/:id', async function (req, res, next) {
-  let id = Number(req.params.id)
+  let id = req.params.id
   let message = req.body.message
 
   try {
diff --git a/app/api/driver.js b/app/api/driver.js
index babb9971af492ac6dbd0073f658bbb0dd52a7ef3..9bbeea02f14b095094b3c34d2ae362edb32b5cb8 100644
--- a/app/api/driver.js
+++ b/app/api/driver.js
@@ -15,7 +15,7 @@ let app = express.Router()
 
 // <root>/driver/<id>/wait
 app.post('/:id/wait', async function (req, res, next) {
-  let id = Number(req.params.id)
+  let id = req.params.id
 
   try {
     let userId = await hub.waitAsync(id, function (reject) {
@@ -32,7 +32,7 @@ app.post('/:id/wait', async function (req, res, next) {
 
 // <root>/driver/<id>/pick
 app.post('/:id/pick', function (req, res) {
-  let id = Number(req.params.id)
+  let id = req.params.id
   let userId = req.body.user_id
 
   // Pick driver by user.
diff --git a/app/service/db.js b/app/service/db.js
index 6ce5ce691014996a40297115895b0f389925df25..901512eb50fe1e7da60bb907749ef548a2521edb 100644
--- a/app/service/db.js
+++ b/app/service/db.js
@@ -10,9 +10,9 @@ const mongoose = require('mongoose')
 mongoose.connect(process.env.MONGODB_URI)
 
 let ChatHistorySchema = mongoose.Schema({
-  participant_ids: [Number],
+  participant_ids: [String],
   chats: [{
-    owner_id: Number,
+    owner_id: String,
     content: String
   }]
 })