网站备案前置审批文件建一个app平台的费用多少

连接数据库

我们首先创建一个DBManager类，通过这个类new出来的对象管理一个数据库
具体关于indexedDB的相关内容可以看我的这篇博客
indexedDB

class DBManager{}

我们首先需要打开数据库，打开数据库需要数据库名和该数据库的版本

constructor(dbName, version) {this.dbName = dbName;this.version = version;this.db = null
}

在constructor中我们先初始化数据库相关信息，dbName为该对象管理的数据库的数据库名，version为该数据库的版本，db为该数据库的IDBDatabase对象
现在我们开始实现openDB方法

openDB() {return new Promise((resolve, reject) => {const cmd = indexedDB.open(this.dbName, this.version)cmd.onsuccess = (event) => {console.log('数据库打开成功')this.db = event.target.resultresolve(this.db)}cmd.onerror = (event) => {console.log('数据库打开失败')reject(event.target.error)}})
}

因为打开数据库涉及i/o操作，所以是异步的，所以我们需要返回一个Promise

关闭数据库

当数据库使用完毕，为了节省资源，我们可以选择断开数据库的连接

closeDB() {if (this.db) {console.log('关闭数据库')this.db.close()this.db = null}
}

删除数据库

如果数据库某一天不在使用，我们可以选择删除这个数据库来节省资源

deleteDB() {return new Promise((resolve, reject) => {const cmd = indexedDB.deleteDatabase(this.dbName)cmd.onsuccess = (event) => {console.log('数据库删除成功')resolve()}cmd.onerror = (event) => {console.log('数据库删除失败')reject(event.target.error)}})
}

同样，删除数据库是异步的，我们需要返回一个Promise

我们接下来来测试一下

(async function () {const db = new DBManager("student", 1)await db.openDB()await db.closeDB()await db.deleteDB()
})()

需要注意的是，我们在删除数据库之前必须先断开数据库连接

创建对象仓库

我们接下来需要实现创建对象的方法

createStore(storeName, keyPath, keys) {return new Promise((resolve, reject) => {if (this.db) {console.log('添加存储仓库', storeName)const store = this.db.createObjectStore(storeName, { keyPath: keyPath, autoIncrement: true })if (keys) {keys.forEach(key => {store.createIndex(key, key, { unique: key === keyPath ? true : false })})}resolve(this.db)} else {reject('数据库未打开')}})
}

但是如果我们直接通过调用createStore来创建对象仓库的话浏览器会报错

这是因为针对对象仓库的操作是需要放在db.onupgradeneeded的回调中，所以我们不能直接这么写

数据库的更新

我们可以用一个更新方法来手动触发onupgradeneeded这个事件

updateDB(callback) {return new Promise(async (resolve, reject) => {console.log('数据库升级')if (this.db) {this.closeDB()this.version += 1await this.openDB(callback)resolve(this.db)}else {reject('数据库未打开')}})
}
openDB(callback) {return new Promise((resolve, reject) => {const cmd = indexedDB.open(this.dbName, this.version)cmd.onsuccess = (event) => {console.log('数据库打开成功')this.db = event.target.resultresolve(this.db)}cmd.onerror = (event) => {console.log('数据库打开失败')reject(event.target.error)}if (callback) {cmd.onupgradeneeded = (event) => {this.db = event.target.resultcallback(event)}}})
}

update方法通过调用close和open方法更新数据库，同时将对对象仓库的操作封装成函数传入update方法中，再将这个函数放入open方法中，open方法中通过判断是否传入参数来判断是否需要监听onupgradeneeded事件，因为当用户第一次创建数据库的时候会触发这个事件，而第一次的时候我们是不需要监听的

接下来我们重新处理下createStore里的逻辑

createStore(storeName, keyPath, keys) {return new Promise(async (resolve, reject) => {if (this.db) {await this.updateDB((event) => {console.log('添加存储仓库', storeName)const store = this.db.createObjectStore(storeName, { keyPath: keyPath, autoIncrement: true })if (keys) {keys.forEach(key => {store.createIndex(key, key, { unique: key === keyPath ? true : false })})}})resolve(this.db)} else {reject('数据库未打开')}})
}

接下来我们再来测试一下

(async function () {const db = new DBManager("student", 1)await db.openDB()await db.createStore("student", "id", ['id', 'name', 'age', 'score'])await db.closeDB()await db.deleteDB()
})()

为什么是先打印添加存储仓库，后打印数据库打开？因为当IDBDatabase对象同时出发onsuccess和onupgradeneeded事件时，会先执行onupgradeneeded的回调，然后执行onsuccess中的回调

数据记录的操作

我们接下来实现关于数据记录的方法

增加数据

增加数据记录的逻辑较为简单，调用indexedDB提供的add方法就行

insert(storeName, data) {return new Promise((resolve, reject) => {if (this.db) {const transaction = this.db.transaction(storeName, 'readwrite')const store = transaction.objectStore(storeName)const cmd = store.add(data)cmd.onsuccess = (event) => {console.log('插入数据成功')resolve(event.target.result)}cmd.onerror = (event) => {console.log('插入数据失败')reject(event.target.error)}} else {reject('数据库未打开')}})
}

我们来测试一下

(async function () {const db = new DBManager("student", 1)await db.openDB()await db.createStore("student", "id", ['id', 'name', 'age', 'score'])await db.insert("student", { id: 1, name: "张三", age: 18, score: 90 })await db.insert("student", { id: 2, name: "李四", age: 20, score: 56 })await db.closeDB()await db.deleteDB()
})()

查询数据

查询数据我们需要根据不同的查询方式来实现不同的方法

1. 通过key查询

   queryByKey(storeName, value) {return new Promise((resolve, reject) => {if (this.db) {const transaction = this.db.transaction(storeName, 'readonly')const store = transaction.objectStore(storeName)const cmd = store.get(value)cmd.onsuccess = (event) => {console.log('查询数据成功')resolve(event.target.result)}cmd.onerror = (event) => {console.log('查询数据失败')reject(event.target.error)}} else {reject('数据库未打开')}})
   }
   

2. 查询全部数据记录

   queryAll(storeName) {return new Promise((resolve, reject) => {if (this.db) {const transaction = this.db.transaction(storeName, 'readonly')const store = transaction.objectStore(storeName)const cmd = store.getAll()cmd.onsuccess = (event) => {console.log('查询数据成功')resolve(event.target.result)}cmd.onerror = (event) => {console.log('查询数据失败')reject(event.target.error)}} else {reject('数据库未打开')}})
   }
   

3. 通过游标查询

   queryByCursor(storeName, range, direction = "next") {return new Promise((resolve, reject) => {if (this.db) {const transaction = this.db.transaction(storeName, 'readonly')const store = transaction.objectStore(storeName)const cursor = range ? store.openCursor(range, direction) : store.openCursor()const result = []cursor.onsuccess = (event) => {const cursor = event.target.resultif (cursor) {result.push(cursor.value)cursor.continue()} else {console.log('查询数据成功')resolve(result)}}cursor.onerror = (event) => {console.log('查询数据失败')reject(event.target.error)}} else {reject('数据库未打开')}})
   }
   

4. 通过指定key-value查询

   queryByIndex(storeName, indexName, value) {return new Promise((resolve, reject) => {if (this.db) {const transaction = this.db.transaction(storeName, 'readonly')const store = transaction.objectStore(storeName)const cmd = store.index(indexName).get(value)cmd.onsuccess = (event) => {console.log('查询数据成功')resolve(event.target.result)}cmd.onerror = (event) => {console.log('查询数据失败')reject(event.target.error)}} else {reject('数据库未打开')}})
   }
   

我们现在来测试一下

(async function () {const db = new DBManager("student", 1)await db.openDB()await db.createStore("student", "id", ['id', 'name', 'age', 'score'])await db.insert("student", { id: 1, name: "张三", age: 18, score: 90 })await db.insert("student", { id: 2, name: "李四", age: 20, score: 56 })await db.insert("student", { id: 3, name: "王五", age: 19, score: 80 })await db.insert("student", { id: 4, name: "赵六", score: 70 })const result = await db.queryByIndex("student", "age", 18)console.log(result)const result2 = await db.queryByKey("student", 3)console.log(result2)const result3 = await db.queryByCursor("student")console.log(result3)const result4 = await db.queryByCursor("student", IDBKeyRange.only(4))console.log(result4)const result5 = await db.queryAll("student")console.log(result5)await db.closeDB()await db.deleteDB()
})()

更新数据

更新数据记录也是通过调用indexedDB中的put方法来实现

update(storeName, key, data) {return new Promise((resolve, reject) => {if (this.db) {const transaction = this.db.transaction(storeName, 'readwrite')const store = transaction.objectStore(storeName)const cmd = store.put(data)cmd.onsuccess = (event) => {console.log('更新数据成功')resolve(event.target.result)}cmd.onerror = (event) => {console.log('更新数据失败')reject(event.target.error)}} else {reject('数据库未打开')}})
}

删除数据

更新数据记录也是通过调用indexedDB中的delete方法来实现

delete(storeName, key) {return new Promise((resolve, reject) => {if (this.db) {const transaction = this.db.transaction(storeName, 'readwrite')const store = transaction.objectStore(storeName)const cmd = store.delete(key)cmd.onsuccess = (event) => {console.log('删除数据成功')resolve(event.target.result)}cmd.onerror = (event) => {console.log('删除数据失败')reject(event.target.error)}} else {reject('数据库未打开')}})
}

完整代码

最后我们来看一下完整代码

class DBManager {constructor(dbName, version) {this.dbName = dbName;this.version = version;this.db = null}openDB(callback) {return new Promise((resolve, reject) => {const cmd = indexedDB.open(this.dbName, this.version)cmd.onsuccess = (event) => {console.log('数据库打开成功')this.db = event.target.resultresolve(this.db)}cmd.onerror = (event) => {console.log('数据库打开失败')reject(event.target.error)}if (callback) {cmd.onupgradeneeded = (event) => {this.db = event.target.resultcallback(event)}}})}closeDB() {if (this.db) {console.log('关闭数据库')this.db.close()this.db = null}}deleteDB() {return new Promise((resolve, reject) => {const cmd = indexedDB.deleteDatabase(this.dbName)cmd.onsuccess = (event) => {console.log('数据库删除成功')resolve()}cmd.onerror = (event) => {console.log('数据库删除失败')reject(event.target.error)}})}updateDB(callback) {return new Promise(async (resolve, reject) => {console.log('数据库升级')if (this.db) {this.closeDB()this.version += 1await this.openDB(callback)resolve(this.db)}else {reject('数据库未打开')}})}createStore(storeName, keyPath, keys) {return new Promise(async (resolve, reject) => {if (this.db) {await this.updateDB((event) => {console.log('添加存储仓库', storeName)const store = this.db.createObjectStore(storeName, { keyPath: keyPath, autoIncrement: true })if (keys) {keys.forEach(key => {store.createIndex(key, key, { unique: key === keyPath ? true : false })})}})resolve(this.db)} else {reject('数据库未打开')}})}deleteStore(storeName) {return new Promise(async (resolve, reject) => {if (this.db) {await this.updateDB((event) => {console.log('删除存储仓库', storeName)const store = this.db.deleteObjectStore(storeName)})resolve(this.db)} else {reject('数据库未打开')}})}insert(storeName, data) {return new Promise((resolve, reject) => {if (this.db) {const transaction = this.db.transaction(storeName, 'readwrite')const store = transaction.objectStore(storeName)const cmd = store.add(data)cmd.onsuccess = (event) => {console.log('插入数据成功')resolve(event.target.result)}cmd.onerror = (event) => {console.log('插入数据失败')reject(event.target.error)}} else {reject('数据库未打开')}})}update(storeName, key, data) {return new Promise((resolve, reject) => {if (this.db) {const transaction = this.db.transaction(storeName, 'readwrite')const store = transaction.objectStore(storeName)const cmd = store.put(data)cmd.onsuccess = (event) => {console.log('更新数据成功')resolve(event.target.result)}cmd.onerror = (event) => {console.log('更新数据失败')reject(event.target.error)}} else {reject('数据库未打开')}})}delete(storeName, key) {return new Promise((resolve, reject) => {if (this.db) {const transaction = this.db.transaction(storeName, 'readwrite')const store = transaction.objectStore(storeName)const cmd = store.delete(key)cmd.onsuccess = (event) => {console.log('删除数据成功')resolve(event.target.result)}cmd.onerror = (event) => {console.log('删除数据失败')reject(event.target.error)}} else {reject('数据库未打开')}})}queryByKey(storeName, value) {return new Promise((resolve, reject) => {if (this.db) {const transaction = this.db.transaction(storeName, 'readonly')const store = transaction.objectStore(storeName)const cmd = store.get(value)cmd.onsuccess = (event) => {console.log('查询数据成功')resolve(event.target.result)}cmd.onerror = (event) => {console.log('查询数据失败')reject(event.target.error)}} else {reject('数据库未打开')}})}queryAll(storeName) {return new Promise((resolve, reject) => {if (this.db) {const transaction = this.db.transaction(storeName, 'readonly')const store = transaction.objectStore(storeName)const cmd = store.getAll()cmd.onsuccess = (event) => {console.log('查询数据成功')resolve(event.target.result)}cmd.onerror = (event) => {console.log('查询数据失败')reject(event.target.error)}} else {reject('数据库未打开')}})}queryByIndex(storeName, indexName, value) {return new Promise((resolve, reject) => {if (this.db) {const transaction = this.db.transaction(storeName, 'readonly')const store = transaction.objectStore(storeName)const cmd = store.index(indexName).get(value)cmd.onsuccess = (event) => {console.log('查询数据成功')resolve(event.target.result)}cmd.onerror = (event) => {console.log('查询数据失败')reject(event.target.error)}} else {reject('数据库未打开')}})}queryByCursor(storeName, range, direction = "next") {return new Promise((resolve, reject) => {if (this.db) {const transaction = this.db.transaction(storeName, 'readonly')const store = transaction.objectStore(storeName)const cursor = range ? store.openCursor(range, direction) : store.openCursor()const result = []cursor.onsuccess = (event) => {const cursor = event.target.resultif (cursor) {result.push(cursor.value)cursor.continue()} else {console.log('查询数据成功')resolve(result)}}cursor.onerror = (event) => {console.log('查询数据失败')reject(event.target.error)}} else {reject('数据库未打开')}})}
}