Code example for indexedDB storage
This article brings you code examples about indexedDB storage. It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>indexedDB（浏览器本地存储数据库）</title>
</head>
<body>
<p>IndexedDB 就是浏览器提供的本地数据库，它可以被网页脚本创建和操作。</p>
<p>IndexedDB 允许储存大量数据，提供查找接口，还能建立索引。</p>
<h3>indexedDB特点</h3>
<ol>
<li>键值对存储：采用对象仓库存储数据，所有的数据类型都可以直接存入，主键是独一无二的</li>
<li>异步：</li>
<li>支持事务：IndexedDB 支持事务（transaction），这意味着一系列操作步骤之中，只要有一步失败，整个事务就都取消，数据库回滚到事务发生之前的状态，不存在只改写一部分数据的情况。</li>
<li>同源限制: IndexedDB 受到同源限制，每一个数据库对应创建它的域名。网页只能访问自身域名下的数据库，而不能访问跨域的数据库。</li>
</ol>
<script>
/**
* databaseName:字符串，表示数据库的名字,不存在则新建
* version :第二个参数是整数，表示数据库的版本。默认为1
* 返回一个 IDBRequest 对象 对象通过三种事件error、success、upgradeneeded
*
* 新建数据库与打开数据库是同一个操作。如果指定的数据库不存在，就会新建。不同之处在于,后续的操作主要在upgradeneeded事件的监听函数里面完成
*
* 新建数据步骤：
* step1:新建对象仓库（即新建表
* step2：新建索引
*
* */
//IDBDatabase对象
let db;
//创建或者打开
let request = window.indexedDB.open('newIDB');
//删除数据库
var DBDeleteRequest = window.indexedDB.deleteDatabase('newIDB');
DBDeleteRequest.onerror = function (event) {
console.log('Error');
};
DBDeleteRequest.onsuccess = function (event) {
console.log('success');
};
//error事件--表示打开数据失败
request.onerror = function (event) {
console.log('数据库打开报错');
db.close();
};
request.success = function (event) {
//通过request对象的result属性拿到数据库对象
db = request.result;
console.log(db);
console.log('数据库打开成功')
};
console.log(request);
//onupgradeneeded---如果指定的版本号，大于数据库的实际版本号，就会发生数据库升级事件
request.onupgradeneeded = function (event) {
//通过事件对象的target.result属性，拿到数据库实例。
console.log(event);
//request对象的result属性上面，拿到一个IDBDatabase对象，它表示连接的数据库
db = event.target.result;
let objectStore;
// 更好的写发是判断表是否存在
if (!db.objectStoreNames.contains('newIDB')) {
/**新建数据
* 新建对象仓库（即新建表)
* 新增一张叫做person的表格，主键是id
* */
//主键（key）是默认建立索引的属性。如果没有可以让 IndexedDB 自动生成主键db.createObjectStore('person',{ autoIncrement: true })
objectStore = db.createObjectStore('newIDB', {keyPath: 'id'});
/**
* 新建索引
* 三个参数分别为索引名称、索引所在的属性、配置对象(说明该属性是否包含重复的值）
* **/
objectStore.createIndex('name', 'name', {unique: false});
objectStore.createIndex('email', 'email', {unique: true});
}
};
/**新增数据
* 新增数据指的是向对象仓库写入数据记录。这需要通过事务完成。
* 写入数据需要新建一个事务
* 新建时必须指定表格名称和操作模式（"只读"或"读写"）
* 写入操作是一个异步操作，通过监听连接对象的success事件和error事件，了解是否写入成功。
* **/
function add() {
//通过IDBTransaction.objectStore(name)方法，拿到 IDBObjectStore 对象，再通过表格对象的add()方法，向表格写入一条记录。
var request = db.transaction(['newIDB'], 'readwrite')
.objectStore('newIDB')
.add({id: 1, name: '张三', age: 24, email: 'zhangsan@example.com'});
request.onsuccess = function (event) {
console.log('数据写入成功');
};
request.onerror = function (event) {
console.log('数据写入失败');
}
}
setTimeout(function () {
console.log(db);
add();
}, 2000);
/** 读取数据
*
*读取数据也是通过事务完成。
*
*
* **/
function read() {
//创建是务
let transaction = db.transaction(['newIDB']);
//拿到 IDBObjectStore 对象
let objectStore = transaction.objectStore('newIDB');
//objectStore.get()方法用于读取数据，参数是主键的值。
let request = objectStore.get(1);
//失败监听
request.onerror = function (event) {
console.log('事务失败');
db.close()
};
//成功监听
request.onsuccess = function (event) {
if (request.result) {
console.log('Name: ' + request.result.name);
console.log('Age: ' + request.result.age);
console.log('Email: ' + request.result.email);
} else {
console.log('未获得数据记录');
}
};
}
setTimeout(function () {
read();
}, 4000);
/**遍历数据
*遍历数据表格的所有记录，要使用指针对象 IDBCursor。
*
* */
function readAll() {
let objectStore = db.transaction('newIDB').objectStore('newIDB');
//新建指针对象的openCursor()方法是一个异步操作，所以要监听success事件。
objectStore.openCursor().onsuccess = function (event) {
let cursor = event.target.result;
if (cursor) {
console.log('Id: ' + cursor.key);
console.log('Name: ' + cursor.value.name);
console.log('Age: ' + cursor.value.age);
console.log('Email: ' + cursor.value.email);
cursor.continue();
} else {
console.log('没有更多数据了！');
}
};
}
setTimeout(function () {
readAll();
}, 6000);
/**跟新数据
*更新数据要使用IDBObject.put()方法。
*
* */
function update() {
//put()方法自动更新了主键为1的记录。
let request = db.transaction(['newIDB'], 'readwrite')
.objectStore('newIDB')
.put({id: 1, name: '李四', age: 35, email: 'lisi@example.com'});
request.onsuccess = function (event) {
console.log('数据更新成功');
};
request.onerror = function (event) {
console.log('数据更新失败');
db.close();
}
}
setTimeout(function () {
update();
}, 8000);
/**删除数据
*IDBObjectStore.delete()方法用于删除记录
*
* **/
function remove() {
let request = db.transaction(['newIDB'], 'readwrite')
.objectStore('newIDB')
.delete(1);
request.onsuccess = function (event) {
console.log('数据删除成功');
};
}
// remove();
/**使用索引
* 索引的意义在于，可以让你搜索任意字段，也就是说从任意字段拿到数据记录。如果不建立索引，默认只能搜索主键（即从主键取值）。
* */
function search() {
let request = db.transaction(['newIDB'], 'readonly')
.objectStore('newIDB')
.index('name')
.get('李四');
request.onsuccess = function (e) {
var result = e.target.result;
if (result) {
console.log('搜索成功')
} else {
console.log('搜索失败')
}
}
}
// search();
</script>
</body>
</html>
**注意：使用的时候链接数据库，失败或者完成其他操作关闭数据库；**This article has ended here. For more exciting content, you can pay attention to the JavaScript Video Tutorial column on the PHP Chinese website!
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