IndexedDB - 范围
当我们不想一次获取所有数据时，我们可以使用范围。 当我们想要获取特定范围内的数据时，我们只使用范围。 我们使用 IDBKeyRange 对象定义范围。 该对象有 4 个方法，分别是 −
- upperBound()
- lowerBound()
- bound()
- only()
语法
IDBKeyRange.lowerBound(indexKey); IDBKeyRange.upperBound(indexKey); IDBKeyRange.bound(lowerIndexKey, upperIndexKey);
以下是各种范围代码的列表 −
| S.No. | 范围代码和描述 |
|---|---|
| 1 | All keys ≥ a DBKeyRange.lowerBound(a) |
| 2 | All keys > a IDBKeyRange.lowerBound(a, true) |
| 3 | All keys ≤ b IDBKeyRange.upperBound(b) |
| 4 | All keys < b IDBKeyRange.upperBound(b, true) |
| 5 | All keys ≥ a && ≤ b IDBKeyRange.bound(a, b) |
| 6 | All keys > a &&< b IDBKeyRange.bound(a, b, true, true) |
| 7 | All keys > a && ≤ b IDBKeyRange.bound(a, b, true, false) |
| 8 | All keys ≥ a && < b IDBKeyRange.bound(a, b, false, true) |
| 9 | The key = c IDBKeyRange.only(c) |
我们通常使用索引来使用范围，在语法中，索引键代表索引键路径值。
示例
使用 get() 和 getAll() 方法检索范围代码的各种示例如下 −
class.get(‘student’) class.getAll(IDBKeyRange.bound(‘science’,’math’) class.getAll(IDBKeyRange.upperbound(‘science’,true) class.getAll() class.getAllKeys(IDBKeyRange.lowerbound(‘student’,true))
HTML 示例
考虑下面的 HTML 示例来获取范围代码 −
<!DOCTYPE html>
<html lang="en">
<head>
<title>Document</title>
</head>
<body>
<script>
const request = indexedDB.open("botdatabase",1);
request.onupgradeneeded = function(){
const db = request.result;
const store = db.createObjectStore("bots",{ keyPath: "id"});
store.createIndex("branch_db",["branch"],{unique: false});
}
request.onsuccess = function(){
document.write("database opened successfully");
const db = request.result;
const transaction=db.transaction("bots","readwrite");
const store = transaction.objectStore("bots");
const branchIndex = store.index("branch_db");
store.add({id: 1, name: "jason",branch: "IT"});
store.add({id: 2, name: "praneeth",branch: "CSE"});
store.add({id: 3, name: "palli",branch: "EEE"});
store.add({id: 4, name: "abdul",branch: "IT"});
store.put({id: 4, name: "deevana",branch: "CSE"});
const upperquery =store.getAll(IDBKeyRange.upperBound('2', true));
upperquery.onsuccess = function(){
document.write("upperquery",upperquery.result);
}
transaction.oncomplete = function(){
db.close;
}
}
</script>
</body>
</html>
输出
database opened successfully
upperquery (4) [{...}, {...}, {...}, {...}]
arg1: (4) [{...}, {...}, {...}, {...}]
0: {id: 1, name: 'jason', branch: 'IT'}
1: {id: 2, name: 'praneeth', branch: 'CSE'}
2: {id: 3, name: 'palli', branch: 'EEE'}
3: {id: 4, name: 'deevana', branch: 'CSE'}
length: 4
[[Prototype]]: Array(0)
[[Prototype]]: Object
