diff --git a/packages/core/__tests__/notes.test.js b/packages/core/__tests__/notes.test.js
index 080dd995e..6d91c4cb3 100644
--- a/packages/core/__tests__/notes.test.js
+++ b/packages/core/__tests__/notes.test.js
@@ -64,7 +64,22 @@ test("add note", () =>
     expect(id).toBeDefined();
     let note = db.notes.get(id);
     expect(note).toBeDefined();
-    expect(note.content).toStrictEqual(TEST_NOTE.content);
+    expect(note.content.text).toStrictEqual(TEST_NOTE.content.text);
+  }));
+
+test("get delta of note", () =>
+  noteTest().then(async ({ db, id }) => {
+    expect(id).toBeDefined();
+    let delta = await db.notes.delta(id);
+    expect(delta).toStrictEqual(TEST_NOTE.content.delta);
+  }));
+
+test("delete note", () =>
+  noteTest().then(async ({ db, id }) => {
+    expect(id).toBeDefined();
+    await db.notes.delete(id);
+    let note = db.notes.get(id);
+    expect(note).toBeUndefined();
   }));
 
 test("get all notes", () =>
@@ -102,7 +117,7 @@ test("update note", () =>
     id = await db.notes.add(noteData);
     let note = db.notes.get(id);
     expect(note.title).toBe(noteData.title);
-    expect(note.content).toStrictEqual(noteData.content);
+    expect(note.content.text).toStrictEqual(noteData.content.text);
     expect(note.pinned).toBe(true);
     expect(note.favorite).toBe(true);
   }));
@@ -226,7 +241,7 @@ test("lock and unlock note", () =>
     expect(note.locked).toBe(true);
     expect(note.content.iv).toBeDefined();
     note = await db.notes.unlock(id, "password123");
-    expect(note.dateCreated).toBe(id);
+    expect(note.id).toBe(id);
     expect(note.content.text).toBe(TEST_NOTE.content.text);
     await db.notes.unlock(id, "password123", true);
     note = db.notes.get(id);
diff --git a/packages/core/collections/notes.js b/packages/core/collections/notes.js
index e2ff1aa99..22aa06c4c 100644
--- a/packages/core/collections/notes.js
+++ b/packages/core/collections/notes.js
@@ -1,12 +1,14 @@
-import Collection from "../database/collection";
+import CachedCollection from "../database/cached-collection";
 import fuzzysearch from "fuzzysearch";
 import Tags from "./tags";
 import { groupBy } from "../utils";
+import sort from "fast-sort";
 import {
   getWeekGroupFromTimestamp,
   months,
   getLastWeekTimestamp
 } from "../utils/date";
+import Storage from "../database/storage";
 var tfun = require("transfun/transfun.js").tfun;
 if (!tfun) {
   tfun = global.tfun;
@@ -14,7 +16,8 @@ if (!tfun) {
 
 export default class Notes {
   constructor(context) {
-    this.collection = new Collection(context, "notes");
+    this.collection = new CachedCollection(context, "notes");
+    this.deltaStorage = new Storage(context);
     this.tagsCollection = new Tags(context);
   }
 
@@ -25,7 +28,7 @@ export default class Notes {
   async add(noteArg) {
     if (!noteArg) return;
 
-    let id = noteArg.id || Date.now();
+    let id = noteArg.id || Date.now().toString() + "_note";
     let oldNote = this.get(id);
     let note = {
       ...oldNote,
@@ -37,11 +40,13 @@ export default class Notes {
       return;
     }
 
+    await this.deltaStorage.write(id + "_delta", note.content.delta);
+
     note = {
       id,
       type: "note",
       title: getNoteTitle(note),
-      content: getNoteContent(note),
+      content: getNoteContent(note, id),
       pinned: !!note.pinned,
       locked: !!note.locked,
       notebook: note.notebook || {},
@@ -50,7 +55,7 @@ export default class Notes {
       favorite: !!note.favorite,
       headline: getNoteHeadline(note),
       dateEdited: Date.now(),
-      dateCreated: id
+      dateCreated: note.dateCreated || Date.now()
     };
 
     if (oldNote) {
@@ -62,7 +67,11 @@ export default class Notes {
     }
 
     await this.collection.addItem(note);
-    return id;
+    return note.id;
+  }
+
+  async delta(id) {
+    return await this.deltaStorage.read(id + "_delta");
   }
 
   get(id) {
@@ -103,7 +112,8 @@ export default class Notes {
     switch (by) {
       case "abc":
         return groupBy(
-          notes.sort((a, b) => a.title.localeCompare(b.title)),
+          //notes.sort((a, b) => a.title.localeCompare(b.title)),
+          sort(notes).asc(t => t.title),
           note => note.title[0].toUpperCase(),
           special
         );
@@ -266,12 +276,13 @@ function getNoteTitle(note) {
     .trim();
 }
 
-function getNoteContent(note) {
+function getNoteContent(note, id) {
   if (note.locked) {
     return note.content;
   }
+
   return {
     text: note.content.text.trim(),
-    delta: note.content.delta
+    delta: id + "_delta"
   };
 }
diff --git a/packages/core/collections/tags.js b/packages/core/collections/tags.js
index 2cde46643..b3f02df31 100644
--- a/packages/core/collections/tags.js
+++ b/packages/core/collections/tags.js
@@ -1,8 +1,8 @@
-import Collection from "../database/collection";
+import CachedCollection from "../database/cached-collection";
 
 export default class Tags {
   constructor(context) {
-    this.collection = new Collection(context, "tags");
+    this.collection = new CachedCollection(context, "tags");
   }
 
   async add(id) {
diff --git a/packages/core/database/collection.js b/packages/core/database/cached-collection.js
similarity index 82%
rename from packages/core/database/collection.js
rename to packages/core/database/cached-collection.js
index 8a6f8e49d..e6654d5a4 100644
--- a/packages/core/database/collection.js
+++ b/packages/core/database/cached-collection.js
@@ -1,6 +1,6 @@
 import Indexer from "./indexer";
 
-export default class Collection {
+export default class CachedCollection {
   constructor(context, type) {
     this.map = new Map();
     this.indexer = new Indexer(context, type);
@@ -14,6 +14,8 @@ export default class Collection {
   }
 
   async addItem(item) {
+    if (!item.id) throw new Error("The item must contain the id field.");
+
     let exists = this.map.has(item.id);
     await this.updateItem(item);
     if (!exists) {
@@ -22,6 +24,8 @@ export default class Collection {
   }
 
   async updateItem(item) {
+    if (!item.id) throw new Error("The item must contain the id field.");
+
     this.map.set(item.id, item);
     await this.indexer.write(item.id, item);
   }
diff --git a/packages/core/database/indexer.js b/packages/core/database/indexer.js
index 73469b56f..f71e8af60 100644
--- a/packages/core/database/indexer.js
+++ b/packages/core/database/indexer.js
@@ -11,18 +11,16 @@ export default class Indexer extends Storage {
     this.indices = (await this.read(this.type)) || [];
   }
 
+  async exists(key) {
+    return this.indices.includes(key);
+  }
+
   async index(key) {
-    if (this.indices.length <= 0) {
-      this.indices = (await this.read(this.type)) || [];
-    }
     this.indices[this.indices.length] = key;
     await this.write(this.type, this.indices);
   }
 
   async getIndices() {
-    if (this.indices.length <= 0) {
-      this.indices = (await this.read(this.type)) || [];
-    }
     return this.indices;
   }
 
diff --git a/packages/core/database/storage.js b/packages/core/database/storage.js
index ce107ca16..f8bbe1ac4 100644
--- a/packages/core/database/storage.js
+++ b/packages/core/database/storage.js
@@ -1,15 +1,13 @@
-import Convert from "../utils/convert";
-
 export default class Storage {
   constructor(context) {
     this.storage = context;
   }
   async write(key, data) {
-    await this.storage.write(key, Convert.toString(data));
+    await this.storage.write(key, data);
   }
   async read(key) {
     let data = await this.storage.read(key);
-    return Convert.fromString(data);
+    return data;
   }
   clear() {
     this.storage.clear();
diff --git a/packages/core/package.json b/packages/core/package.json
index e6e8acb33..00d748bfe 100644
--- a/packages/core/package.json
+++ b/packages/core/package.json
@@ -16,8 +16,9 @@
     "test": "jest"
   },
   "dependencies": {
+    "fast-sort": "^2.0.1",
     "fuzzysearch": "^1.0.3",
-    "transfun": "^1.0.2",
-    "node-fetch": "^2.6.0"
+    "node-fetch": "^2.6.0",
+    "transfun": "^1.0.2"
   }
 }
diff --git a/packages/core/yarn.lock b/packages/core/yarn.lock
index 63125eb3a..b709782fe 100644
--- a/packages/core/yarn.lock
+++ b/packages/core/yarn.lock
@@ -2171,6 +2171,11 @@ fast-levenshtein@~2.0.6:
   resolved "https://registry.yarnpkg.com/fast-levenshtein/-/fast-levenshtein-2.0.6.tgz#3d8a5c66883a16a30ca8643e851f19baa7797917"
   integrity sha1-PYpcZog6FqMMqGQ+hR8Zuqd5eRc=
 
+fast-sort@^2.0.1:
+  version "2.0.1"
+  resolved "https://registry.yarnpkg.com/fast-sort/-/fast-sort-2.0.1.tgz#71d932d2de380d0d6ca449fdc5dbdefdc437e84a"
+  integrity sha512-61gSQXW5KavRau+RBlQbpD3q+tUyrHSKiU/wob4RP58s99uIpydII6MaRpA+t6Td6/WhvU0lgL8UoMPKKv4xYg==
+
 fb-watchman@^2.0.0:
   version "2.0.0"
   resolved "https://registry.yarnpkg.com/fb-watchman/-/fb-watchman-2.0.0.tgz#54e9abf7dfa2f26cd9b1636c588c1afc05de5d58"