indexeddb

Khóa học miễn phí IndexedDB – Indexes nhận dự án làm có lương

Posted on by user

IndexedDB – Indexes

Indexes are a kind of object store used to retrieve data from the reference object stored by a specified property. Even though an index is inside the reference object store and contains the same data, instead of the reference store”s primary key it uses the specified property as its key path.

Indexes are used to define a unique constraint on your data and they are made when the object stores are created. To create an index, call the createIndex method on an object store instance −

Syntax

var myIDBIndex = objectStore.createIndex(indexName, keyPath);
var myIDBIndex = objectStore.createIndex(indexName, keyPath, objectParameters);

This method creates and returns an index object. The method creates an index that takes the following arguments −

  • Index name − The name of the index.

  • Keypath − We mention the primary key here.

  • Object Parameters − There are two object parameters.

  • Unique − Duplicate values cannot be added.

  • Multi entry − If true, the index will add an entry in the index for each array element when the keyPath resolves to an Array. If false, it will add one single entry containing the Array.

Example

The following example shows the implementation of indexes in an object store −

<!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"});
         transaction.oncomplete = function(){
            db.close;
         }
      }
   </script>
</body>
</html>

Output

branchIndex:
1
[''CSE'']
0: "CSE"
length: 1
4
{id: 4, name: ''deevana'', branch: ''CSE''}
branch: "CSE"
id: 4
name: "deevana"
2
[''EEE'']
0: "EEE"
length: 1
3
{id: 3, name: ''palli'', branch: ''EEE''}
branch: "EEE"
id: 3
name: "palli"
3
[''IT'']
0: "IT"
length: 1
1
{id: 1, name: ''jason'', branch: ''IT''}
branch: "IT"
id: 1
name: "jason"

Khóa học lập trình tại Toidayhoc vừa học vừa làm dự án vừa nhận lương: Khóa học lập trình nhận lương tại trung tâm Toidayhoc

user