diff --git a/src/core/ArSyncStore.ts b/src/core/ArSyncStore.ts
index 2e0639a..af5053e 100644
--- a/src/core/ArSyncStore.ts
+++ b/src/core/ArSyncStore.ts
@@ -1,5 +1,7 @@
 import ArSyncApi from './ArSyncApi'
-export type Request = { api: string; query: any; params?: any; id?: any }
+export type Request = { api: string; query: any; params?: any; id?: IDType }
+
+type IDType = number | string
 
 class ModelBatchRequest {
   timer: number | null = null
@@ -7,8 +9,8 @@ class ModelBatchRequest {
     Map<string,
       {
         query,
-        requests: Map<number, {
-          id: number
+        requests: Map<IDType, {
+          id: IDType
           model?
           callbacks: {
             resolve: (model: any) => void
@@ -18,7 +20,7 @@ class ModelBatchRequest {
       }
     >
   >()
-  fetch(api: string, query, id: number) {
+  fetch(api: string, query, id: IDType) {
     this.setTimer()
     return new Promise((resolve, reject) => {
       const queryJSON = JSON.stringify(query)
@@ -68,7 +70,7 @@ type ParsedQuery = {
   params: any
 } | {}
 
-type SyncField = { id: number; keys: string[] }
+type SyncField = { id: IDType; keys: string[] }
 type Unsubscribable = { unsubscribe: () => void }
 
 class ArSyncContainerBase {
@@ -227,12 +229,12 @@ class ArSyncContainerBase {
 type NotifyData = {
   action: 'add' | 'remove' | 'update'
   class: string
-  id: number
+  id: IDType
   field?: string
 }
 
 class ArSyncRecord extends ArSyncContainerBase {
-  id: number
+  id: IDType
   root: ArSyncStore
   query
   queryAttributes
@@ -426,7 +428,7 @@ class ArSyncCollection extends ArSyncContainerBase {
   data: any[]
   children: ArSyncRecord[]
   aliasOrderKey = 'id'
-  fetching = new Set<number>()
+  fetching = new Set<IDType>()
   constructor(parentSyncKeys: string[], path: string, query, data: any[], request, root: ArSyncStore, parentModel: ArSyncRecord | null, parentKey: string | null){
     super()
     this.root = root
@@ -466,7 +468,7 @@ class ArSyncCollection extends ArSyncContainerBase {
   }
   replaceData(data: any[] | { collection: any[]; ordering: Ordering }, parentSyncKeys: string[]) {
     this.setSyncKeys(parentSyncKeys)
-    const existings = new Map<number, ArSyncRecord>()
+    const existings = new Map<IDType, ArSyncRecord>()
     for (const child of this.children) existings.set(child.id, child)
     let collection: any[]
     if (Array.isArray(data)) {
@@ -502,7 +504,7 @@ class ArSyncCollection extends ArSyncContainerBase {
     for (const el of newData) this.data.push(el)
     this.subscribeAll()
   }
-  consumeAdd(className: string, id: number) {
+  consumeAdd(className: string, id: IDType) {
     const { first, last, direction } = this.ordering
     const limit = first || last
     if (this.children.find(a => a.id === id)) return
@@ -585,7 +587,7 @@ class ArSyncCollection extends ArSyncContainerBase {
       this.data.sort((a, b) => a[orderKey] > b[orderKey] ? -1 : +1)
     }
   }
-  consumeRemove(id: number) {
+  consumeRemove(id: IDType) {
     const idx = this.children.findIndex(a => a.id === id)
     this.fetching.delete(id) // To cancel consumeAdd
     if (idx < 0) return
@@ -610,7 +612,7 @@ class ArSyncCollection extends ArSyncContainerBase {
     super.onChange(path, data)
     if (path[1] === this.aliasOrderKey) this.markAndSort()
   }
-  markAndSet(id: number, data) {
+  markAndSet(id: IDType, data) {
     this.mark()
     const idx = this.children.findIndex(a => a.id === id)
     if (idx >= 0) this.data[idx] = data
diff --git a/test/model.rb b/test/model.rb
index e80b0c0..9add4db 100644
--- a/test/model.rb
+++ b/test/model.rb
@@ -17,6 +17,9 @@ class User < BaseRecord
 end
 
 class Post < BaseRecord
+  before_validation do
+    self.id ||= '%08d' % (Post.maximum(:id).to_i + 1)
+  end
   self.table_name = :posts
   belongs_to :user
   has_many :comments, dependent: :destroy
diff --git a/test/seed.rb b/test/seed.rb
index 3af779f..54eaaaf 100644
--- a/test/seed.rb
+++ b/test/seed.rb
@@ -8,7 +8,7 @@
   create_table :users do |t|
     t.string :name
   end
-  create_table :posts do |t|
+  create_table :posts, id: :string do |t|
     t.references :user
     t.string :title
     t.text :body
@@ -16,7 +16,7 @@
   end
 
   create_table :comments do |t|
-    t.references :post
+    t.references :post, type: :string
     t.references :user
     t.text :body
     t.timestamps
@@ -36,7 +36,7 @@
 user_ids = User.ids
 
 posts = 16.times.map do |i|
-  { user_id: user_ids.sample, title: "Post#{i}", body: "post #{i}" }
+  { id: '%08d' % (i + 1), user_id: user_ids.sample, title: "Post#{i}", body: "post #{i}" }
 end
 Post.import posts
 post_ids = Post.ids
diff --git a/test/sync_test.rb b/test/sync_test.rb
index dc5e06d..a575d6d 100644
--- a/test/sync_test.rb
+++ b/test/sync_test.rb
@@ -180,7 +180,7 @@ class Schema
     runner.eval_script <<-JAVASCRIPT
       global.postModel = new ArSyncModel({
         api: 'post',
-        params: { id: #{post.id} },
+        params: { id: #{post.id.to_json} },
         query: {
           comments: {
             params: { orderBy: 'body', direction: '#{direction}' },
@@ -214,7 +214,7 @@ class Schema
     runner.eval_script <<-JAVASCRIPT
       global.postModel = new ArSyncModel({
         api: 'post',
-        params: { id: #{post.id} },
+        params: { id: #{post.id.to_json} },
         query: {
           comments: {
             params: { #{first_last}: 3, direction: '#{direction}' },
@@ -295,7 +295,7 @@ class Schema
     runner.eval_script <<~JAVASCRIPT
       global.postModel = new ArSyncModel({
         api: 'post',
-        params: { id: #{post.id} },
+        params: { id: #{post.id.to_json} },
         query: ['id','titleChars']
       })
     JAVASCRIPT
@@ -315,7 +315,7 @@ class Schema
   runner.eval_script <<~JAVASCRIPT
     global.postModel = new ArSyncModel({
       api: 'post',
-      params: { id: #{post.id} },
+      params: { id: #{post.id.to_json} },
       query: { comments: 'editedStarCount' }
     })
   JAVASCRIPT
@@ -333,7 +333,7 @@ class Schema
   runner.eval_script <<~JAVASCRIPT
     global.postsModel = new ArSyncModel({
       api: 'Post',
-      params: { ids: [#{post1.id}, #{post2.id}] },
+      params: { ids: [#{post1.id.to_json}, #{post2.id.to_json}] },
       query: ['id', 'title']
     })
   JAVASCRIPT
@@ -348,8 +348,8 @@ class Schema
   post1 = Post.first
   post2 = Post.second
   runner.eval_script <<~JAVASCRIPT
-    global.p1 = new ArSyncModel({ api: 'Post', id: #{post1.id}, query: 'title' })
-    global.p2 = new ArSyncModel({ api: 'Post', id: #{post2.id}, query: 'title' })
+    global.p1 = new ArSyncModel({ api: 'Post', id: #{post1.id.to_json}, query: 'title' })
+    global.p2 = new ArSyncModel({ api: 'Post', id: #{post2.id.to_json}, query: 'title' })
   JAVASCRIPT
   runner.assert_script 'p1.data && p2.data'
   runner.assert_script '[p1.data.title, p2.data.title]', to_be: [post1.title, post2.title]
@@ -401,8 +401,8 @@ class Schema
   runner.eval_script <<~JAVASCRIPT
     global.data1 = {}
     global.data2 = {}
-    ArSyncApi.syncFetch({ api: 'Post', id: #{post.id}, query: 'title' }).then(data => { global.data1 = data })
-    ArSyncApi.fetch({ api: 'Post', id: #{post.id}, query: 'title' }).then(data => { global.data2 = data })
+    ArSyncApi.syncFetch({ api: 'Post', id: #{post.id.to_json}, query: 'title' }).then(data => { global.data1 = data })
+    ArSyncApi.fetch({ api: 'Post', id: #{post.id.to_json}, query: 'title' }).then(data => { global.data2 = data })
   JAVASCRIPT
   runner.assert_script 'data1.title', to_be: post.title
   runner.assert_script 'data2.title', to_be: post.title
diff --git a/test/type_test.ts b/test/type_test.ts
index e166533..d351232 100644
--- a/test/type_test.ts
+++ b/test/type_test.ts
@@ -27,7 +27,7 @@ isOK<IsEqual<typeof data2, { id: number; name: string | null }>>()
 const data3 = new ArSyncModel({ api: 'currentUser', query: '*' }).data!
 isOK<IsEqual<typeof data3, { id: number; name: string | null; posts: {}[]; postOrNull: {} | null; itemWithId: any; itemsWithId: any }>>()
 const data4 = new ArSyncModel({ api: 'currentUser',  query: { posts: 'id' } }).data!
-isOK<IsEqual<typeof data4, { posts: { id: number }[] }>>()
+isOK<IsEqual<typeof data4, { posts: { id: string }[] }>>()
 const data5 = new ArSyncModel({ api: 'currentUser', query: { posts: '*' } }).data!
 data5.posts[0].id; data5.posts[0].user; data5.posts[0].body
 isOK<TypeIncludes<typeof data5.posts[0], { body: string | null, comments: {}[] }>>()
@@ -46,11 +46,11 @@ isOK<HasExtraField<typeof data11, 'commmments'>>()
 const data12 = new ArSyncModel({ api: 'currentUser', query: { posts: { params: { first: 4 }, attributes: 'title' } } }).data!
 isOK<IsEqual<(typeof data12.posts)[0], { title: string | null }>>()
 const data13 = new ArSyncModel({ api: 'currentUser', query: { posts: { params: { first: 4 }, attributes: ['id', 'title'] } } }).data!
-isOK<IsEqual<(typeof data13.posts)[0], { id: number; title: string | null }>>()
+isOK<IsEqual<(typeof data13.posts)[0], { id: string; title: string | null }>>()
 const data14 = new ArSyncModel({ api: 'currentUser', query: { posts: { params: { first: 4 }, attributes: { id: true, title: true } } } }).data!
-isOK<IsEqual<(typeof data14.posts)[0], { id: number; title: string | null }>>()
+isOK<IsEqual<(typeof data14.posts)[0], { id: string; title: string | null }>>()
 const data15 = new ArSyncModel({ api: 'currentUser', query: { posts: ['id', 'title'] } } as const).data!
-isOK<IsEqual<(typeof data15.posts)[0], { id: number; title: string | null }>>()
+isOK<IsEqual<(typeof data15.posts)[0], { id: string; title: string | null }>>()
 const data16 = new ArSyncModel({ api: 'User', id: 1, query: 'name' }).data!
 isOK<IsEqual<typeof data16, { name: string | null }>>()
 const data17 = new ArSyncModel({ api: 'currentUser', query: 'postOrNull' }).data!
@@ -62,6 +62,6 @@ isOK<TypeIncludes<typeof data19, { postOrNull: { title: string | null } | null }
 
 const model = new ArSyncModel({ api: 'currentUser', query: { posts: ['id', 'title'] } } as const)
 let digId = model.dig(['posts', 0, 'id'] as const)
-isOK<IsEqual<typeof digId, number | null | undefined>>()
+isOK<IsEqual<typeof digId, string | null | undefined>>()
 let digTitle = model.dig(['posts', 0, 'title'] as const)
 isOK<IsEqual<typeof digTitle, string | null | undefined>>()