从Indexeddb获取特定ID

Question

在我的项目中,我正在使用浏览器的索引数据库,我想从具有特定ID的数据库中检索一些对象.根据MDN,您可以使用范围来获得所需的结果:

据MDN称:

// Only match "Donna"
var singleKeyRange = IDBKeyRange.only("Donna");

// Match anything past "Bill", including "Bill"
var lowerBoundKeyRange = IDBKeyRange.lowerBound("Bill");

// Match anything past "Bill", but don't include "Bill"
var lowerBoundOpenKeyRange = IDBKeyRange.lowerBound("Bill", true);

// Match anything up to, but not including, "Donna"
var upperBoundOpenKeyRange = IDBKeyRange.upperBound("Donna", true);

// Match anything between "Bill" and "Donna", but not including "Donna"
var boundKeyRange = IDBKeyRange.bound("Bill", "Donna", false, true);

// To use one of the key ranges, pass it in as the first argument of openCursor()/openKeyCursor()
index.openCursor(boundKeyRange).onsuccess = function(event) {
  var cursor = event.target.result;
  if (cursor) {
    // Do something with the matches.
    cursor.continue();
  }
};

但是,如果您希望获得一系列不按顺序且不是顺序的特定ID(例如:[91,819,34,24,501])并且只有一个请求,您会怎么做？

Answer 1

您不能使用单个请求执行此操作，但可以并行触发多个请求：

var keys = [91,819,34,24,501];
var results = [];
keys.forEach(function(key) {
  store.get(key).onsuccess = function(e) {
    results.push(e.target.result);
    if (results.length === keys.length) {
       // you're done!
    }
  };
});

请注意，请求需要按顺序执行，因此results数组的顺序将与数组的顺序匹配keys。如果未找到键，则相应的结果索引将包含undefined.

（有一个对索引数据库的功能请求以直接支持它：https : //github.com/w3c/IndexedDB/issues/19但还没有最终的 API 设计。）

Answer 2

使用光标可以通过按键一次性获取多个对象。

需要对键进行排序。

var keys = [91,819,34,24,501].sort(function(a, b) {
   return a - b;
});
var results = [];
var i = 0;
var cursorReq = store.openCursor();
cursorReq.onsuccess = function(e) {
   var c = e.target.result;
   if(!c) { return; /* done */ }
   while(c.key > keys[i]) {
      i++;
      if(i === keys.length) { return; /* done */ }
   }
   if(c.key === keys[i]) { // found
      results.push(cursor.value);
      c.continue();
   } else { c.continue(keys[i]); }
}