javascript - IndexedDB的IDBCursor中key和primaryKey有什么区别

Question

documentation here says that

键

Returns the cursor's current key. (Cursors also have a key and a value which represent the key and the value of the last iterated record.)

主键

Returns the cursor's current effective key. (If the source of a cursor is an object store, the effective object store of the cursor is that object store and the effective key of the cursor is the cursor's position.)

但是在下面的示例中，两者的使用完全相同，我得到的值也相同:

• https://developer.mozilla.org/en-US/docs/Web/API/IDBCursor/primaryKey
• https://developer.mozilla.org/en-US/docs/Web/API/IDBCursor/key

那么实际区别是什么？

Answer 1

如果您遍历对象存储，它们是相同的。

如果您正在遍历索引，键 是索引键 而primaryKey 是对象中的键商店。

例如:

 book_store = db.createObjectStore('books');
 title_index = store.createIndex('by_title', 'title');

 key = 123;
 value = {title: 'IDB for Newbies', author: 'Alice'};
 book_store.put(value, key);

 book_store.openCursor().onsuccess = function(e) {
   cursor = e.target.result;
   console.log(cursor.key); // logs 123
   console.log(cursor.primaryKey); // logs 123
 };
 title_index.openCursor().onsuccess = function(e) {
   cursor = e.target.result;
   console.log(cursor.key); // logs 'IDB for Newbies'
   console.log(cursor.primaryKey); // logs 123
 };