檢查indexedDB索引是否已經存在

Question

我想在onupgradeneeded上更新我的indexeddb數據庫的其中一個對象庫。我想檢查一下，如果這個索引存在於這個物品庫中，那麼就不需要做任何改變。但如果不是，我想更新它的索引。

Answer 1

var request = indexedDB.open(...); 
request.onupgradeneeded = function(event) { 
    // Get the IDBDatabase connection 
    var db = event.target.result; 

    // This is the implied IDBTransaction instance available when 
    // upgrading, it is type versionchange, and is similar to 
    // readwrite. 
    var tx = event.target.transaction; 

    // Get the store from the transaction. This assumes of course that 
    // you know the store exists, otherwise use 
    // db.objectStoreNames.contains to check first. 
    var store = tx.objectStore('myStore'); 

    // Now check if the index exists 
    if(store.indexNames.contains('myIndex')) { 
    // The store contains an index with that name 
    console.log('The index myIndex exists on store myStore'); 

    // You can also access the index and ensure it has the right 
    // properties you want. If you want to change the properties you 
    // will need to delete the index then recreate it. 
    var index = store.index('myIndex'); 

    // For example 
    if(index.multiEntry) { 
     console.log('myIndex is flagged as a multi-entry index'); 
    } 

    if(index.unique) { 
     console.log('myIndex is flagged with the unique constraint'); 
    } 

    } else { 
    // The store does not contain an index with that name 
    console.log('The index myIndex does not exist on store myStore'); 

    // Can create it here if you want 
    store.createIndex('myIndex', ...); 
    } 

};