Javascript 如何获取按限额返回的项目索引&；降序createAt

这是我第一次使用Parse，到目前为止我很喜欢它，读写数据都很有效

我现在想做一些看似简单的事情，但在解析的上下文中似乎很难实现，我的谷歌fu让我失望

当我找到这样的项目时：

var query = new Parse.Query(CommentClass);
query.limit(2);
query.descending('createdAt');
query.find({
    success: function(object) {
        callback({
            comments: object
        });
    },
    error: function(object, error) {
        console.log('there was an error');
    }
});

---

我想知道总列表中返回项目的索引是什么。如果我的列表有5个项目，这将返回最后创建的2个项目，但是如果没有另一个请求知道列表中项目的数量，这是不可能的。

在解析中没有简单的方法。一种方法是将全局索引保存在单独的对象中。在每个新的注释中，您需要获得这个全局索引，增加它，并将其放入注释中。但如果删除评论，它可能会变得一团糟。下面是一个假设不删除注释的示例：

SequenceForComment.js

// A class called SequenceForComment. Only one row. 
// Only one integer property called 'sequence'.
// You can create the row by using the Parse dashboard in the beginning. 

var SequenceForComment = Parse.Object.extend("SequenceForComment");

function getSequenceForComment(callback) {
  var query = new Parse.Query(SequenceForComment);
  return query.first().then(function (object) {
    // https://parse.com/docs/js/api/classes/Parse.Object.html#methods_increment
    //Increment is atomic.
    object.increment('sequence');
    return object.save();
  }).then(function (object) {
    callback(object.get('sequence'));
  }, function (error) {
    console.log(error);
    callback(undefined);
  });
}

module.exports = {
  getSequenceForComment: getSequenceForComment
};

var SequenceModule = require("cloud/SequenceForComment.js");

Parse.Cloud.beforeSave("Comment", function(request, response) {
  var comment = request.object;

  // First time this comment will be saved.
  // https://parse.com/docs/js/api/classes/Parse.Object.html#methods_isNew
  if (comment.isNew()) {

    // Get a sequence/index for the new comment
    SequenceModule.getSequenceForComment(function(sequence) {
      if (sequence) {
        comment.set("sequence", sequence);
        response.success();
      } else {
        response.error('Could not get a sequence.');
      }
    });
  } else { // Not a new save, already has an index
    response.success();
  }
});

main.js

// A class called SequenceForComment. Only one row. 
// Only one integer property called 'sequence'.
// You can create the row by using the Parse dashboard in the beginning. 

var SequenceForComment = Parse.Object.extend("SequenceForComment");

function getSequenceForComment(callback) {
  var query = new Parse.Query(SequenceForComment);
  return query.first().then(function (object) {
    // https://parse.com/docs/js/api/classes/Parse.Object.html#methods_increment
    //Increment is atomic.
    object.increment('sequence');
    return object.save();
  }).then(function (object) {
    callback(object.get('sequence'));
  }, function (error) {
    console.log(error);
    callback(undefined);
  });
}

module.exports = {
  getSequenceForComment: getSequenceForComment
};

var SequenceModule = require("cloud/SequenceForComment.js");

Parse.Cloud.beforeSave("Comment", function(request, response) {
  var comment = request.object;

  // First time this comment will be saved.
  // https://parse.com/docs/js/api/classes/Parse.Object.html#methods_isNew
  if (comment.isNew()) {

    // Get a sequence/index for the new comment
    SequenceModule.getSequenceForComment(function(sequence) {
      if (sequence) {
        comment.set("sequence", sequence);
        response.success();
      } else {
        response.error('Could not get a sequence.');
      }
    });
  } else { // Not a new save, already has an index
    response.success();
  }
});

---

好的，我会添加一些片段，但是我应该去哪里尝试解决这个问题呢？文档建议了一种方法，但没有进一步解释。索引应该是什么？不仅仅是结果中的项目顺序？它是“列表中的索引”还是“类中的索引（创建）”？列表中的索引，如果我在列表中有4个项目，当我添加一个新项目时，我希望它的索引为4/5，这取决于它是否基于0。您想要的与列表本身给您的行号之间有什么区别？