在给定索引的情况下，如何读取indexeddb自动增量对象库中的对象键 [英] How do I read an objects key in an indexeddb autoincrement objectstore, given an index

问题描述

这个代码形式的问题，我可以用 .put（doc，key）来覆盖对象，但我无法弄清楚如何读取它的密钥

This question in code form, I can use .put(doc, key) to overwrite the object, but I cant figure out how to read its key

// After writing doc1 to an autoincrement
// objectStore, I want to overwrite it 
// later, I only know its index 
// (not its key)

var docs = [
  {'a':'doc1', 'my_index': 'anindex'},
  {'a':'doc2', 'my_index': 'anindex'}
];

indexedDB.deleteDatabase('foo').onsuccess = function () { 

  var idb;
  var req = indexedDB.open('foo');

  function writeDocs(docs) {

    if (!docs.length) { 
      console.log('done writing');
      return;
    }

    var txn = idb.transaction(['some_store_name'], 'readwrite');
    var doc = docs.shift();
    console.log('writing', doc);

    var get = txn.objectStore('some_store_name').index('my_index')
      .get(doc.my_index);

    get.onsuccess = function(e) { 

      var key = null;

      if (e.target.result) { 
        // If there is a result here, I want to overwrite it
        // to do that I need its key, cant find it here?    
        console.log(e.target.result);
      }

      var dataReq = txn.objectStore('some_store_name').put(doc);

      dataReq.onsuccess = function (e) {
        console.log('wroted', e.target.result);
        writeDocs(docs);
      }

      dataReq.onerror = function () { 
        console.log('it broke');
        writeDocs(txn, docs);
      }
    }
  };

  req.onupgradeneeded = function(e) {
    var db = e.target.result;
    db.createObjectStore('some_store_name', {autoIncrement : true})
      .createIndex('my_index', 'my_index', {unique: true});
  };

  req.onsuccess = function(e) { 
    idb = e.target.result;
    writeDocs(docs);
  };
}

推荐答案

  if (e.target.result) {
    // If there is a result here, I want to overwrite it
    // to do that I need its key, cant find it here?    
    console.log(e.target.result);
  }

e.target.result 其实是关键！但仅作为对的回复或添加，而不是获取。您可以将此值用于 put（）将来的数据。

e.target.result is in fact the key! But only as a response to put or add, not a get. You can use this value to put() the data in the future.

使用外线键，例如你有： objectstore.put（数据，密钥）

With out of line keys, like you have: objectstore.put(data, key)

使用内联键，你只需 objectstore.put（data）

更新：问题是你在循环 writeDocs 但是在你的第一个循环中 key 是 null 所以它会抛出一个错误。

Update: The problem is you're looping writeDocs but in your first loop key is null so it throws an error.

这是一个有效的例子。

第二次更新：看起来某些代码可能已添加，或者我之前遗漏了一些内容。除了我上面标记的内容，但您的索引是 unique ，并且您使用相同的 my_index 值两次因此第二个 put（）的错误。我通过在每个页面加载中使 my_index 唯一来避免这个问题。

Second Update: It looks like some code may have been added, or I missed something earlier. In addition to what I have flagged above, but your index is unique and you're using the same my_index value twice, hence the error on second put(). I avoided this problem in my fiddle solution by making my_index unique each pageload.

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