indexeddb - 在 indexedDB 中，如何判断使用 objectStore.put 时记录是更新还是插入？

Question

当使用 put() 将数据插入到带有 indexeddb 的数据存储中时，有没有办法知道记录是插入还是更新？

我想知道记录是否存在。无论哪种方式，我都会插入/更新数据。异步 api 使这变得困难。

Answer 1

另一种模式是使用光标。你节省了一点cpu时间。

req = objStore.openCursor(IDBKeyRange.lowerBound(key))
req.onsuccess = function(ev) {
  var cursor = ev.target.result;
  if (cursor) {
     // do update
    cursor.continue(next_key);
  } else {
     // do create
  }
};

我在http://lists.w3.org/Archives/Public/public-webapps/2012OctDec/0481.html讨论了这个问题

Answer 2

I don't think you can. You could attempt to do add first, which would potentially result in a ConstraintError error. If you get that error, do put instead.

Or just do a get first.

Doing get+put always requires two requests. Doing add+put possibly only one (the add).

Answer 3

您可以通过光标更新：

function insertOrUpdateSomething(db, obj) { 
  var tx = db.transaction('storename','readwrite');
  var store = tx.objectStore('storename');
  store.openCursor(IDBKeyRange.only(obj.id)).onsuccess = function(event) {
   if(event.target.result) {
     console.log('Updating %s', JSON.stringify(obj));
     event.target.result.update(obj);
   } else {
     console.log('Inserting %s', JSON.stringify(obj));
     event.target.add(obj);
  }
};

Answer 4

你可以使用这个功能

SaveOrUpdateDate (db,Table,By,Var,Value,CallbackSuccess, CallbackError){
    var data = db.transaction([Table], "readwrite");
    var object = data.objectStore(Table);
    var index = object.index('by_'+By);
    var request = index.get(String(Var));
    request.onsuccess = function () {
        var result = request.result;
        if(typeof result !== 'undefined'){
            result[Var] = Value;
        }else{
            result = new Object();
            result[By] = Var;
            result[Var] = Value;
        }
        var request2 = object.put(result);
        request2.onsuccess = function(e){
            CallbackSuccess();
        };
        request2.onerror = function(e){
            CallbackError();
        };
    }
}