javascript - BackboneJS 在集合中重新排列模型同时为每个模型维护 0 索引序数属性的最佳方法

Question

我在这里遇到一个问题，我有一个 BackboneJS 模型的集合，每个模型都有一个“序数”属性来跟踪它在集合中的顺序。

这是我的播放数据

var ex_group_test_data = [{

            title: 'PRE EXERCISE',
            id:         0,
            ordinal:    1,

            group_items: [{
                id:         0,
                ordinal:    0,
                title: 'item 1'
            },{
                id:         1,
                ordinal:    1,
                title: 'item 2'
            }]

        },{

            title: 'MAIN PART',
            id:         1,
            ordinal:    0,

            group_items: [{
                id:             2,
                ordinal:        0,
                title:          'item 3',
                description:    'testing descrip'
            },{
                id:         3,
                ordinal:    1,
                title: 'item 4'
            }]

        },{

            title: 'POST EXERCISE BS',
            id:         2,
            ordinal:    2,

            group_items: [{
                id:             2,
                ordinal:        0,
                title:          'item 5',
                description:    'testing descrip'
            },{
                id:         3,
                ordinal:    1,
                title: 'item 6'
            }]

        }];

这是我的主干集合的要点

        Collections.Exercise_Groups = Backbone.Collection.extend({
            model: Models.Exercise_Group,
            comparator: function(model){
                return model.get('ordinal');
            },
            initialize: function(){

                return this;
            }

从简单开始，我希望能够采用一个模型并将其移动 +1 或 -1 序号并保持集合中所有模型的 0 索引。

最终，我想将其提升到这样一个水平，即我可以放入模型或将它们从任何位置移除并仍然保持我的 0 索引，或者采用模型并将其移动 +/- X 位置。

有人推荐了实现此目的的方法吗？

编辑 1

我已经制定了一个解决方案，我可能想在明天真正睡一觉之后优化它。它保持我收藏中模型“序数”的 0 索引，无论我是将模型相对于其原始位置向前还是向后移动。

编辑 2错误，实际上它在边缘案例上有错误。

/**
             * Move model to a specified location. 
             * 
             * @param   int [model id]
             * @param   int [mew item position]
             * @return  this
             */
            move_to: function(m_id, new_pos){

                //keep within range
                if(new_pos < 0)
                    new_pos = 0;
                else if(new_pos > (this.length - 1))
                    new_pos = this.length - 1;


                var model = this.get(m_id),
                    old_pos = model.get('ordinal');


                model.set({
                    ordinal: new_pos
                });
                if(new_pos == old_pos){
                    //trigger associated events
                    this.sort();
                    return this;
                }

                //update indexes of affected models
                this.each(function(m){

                    //ordinal of current model in loop
                    var m_ordinal = m.get('ordinal');

                    //skip if this is the model we just updated
                    if(m.get('id') == m_id)
                        return;

                    if(old_pos < new_pos){
                        //moving down, ordinal is increasing

                        if(m_ordinal <= new_pos && m_ordinal != 0){
                            //this is in the range we care about
                            m.set({
                                ordinal: m.get('ordinal') - 1
                            });

                        }

                    }else if(old_pos > new_pos){
                        //moving up, ordinal is decreasing                  


                        if(m_ordinal >= new_pos && (m_ordinal != (this.length - 1))){
                            //this is in the range we care about
                            m.set({
                                ordinal: m.get('ordinal') + 1
                            });

                        }

                    }

                });

                this.sort();
                return this;

            }

编辑 3好吧，我想我已经解决了所有问题，一些简单的范围问题。这是一些我已经非常彻底地测试过的代码，我相信它可以工作。

/**
                 * Move model to a specified location. 
                 * 
                 * @param   int [model id]
                 * @param   int [mew item position]
                 * @return  this
                 */
                move_to: function(m_id, new_pos){

                    //keep within range
                    if(new_pos < 0)
                        new_pos = 0;
                    else if(new_pos > (this.length - 1))
                        new_pos = this.length - 1;


                    var model = this.get(m_id),
                        old_pos = model.get('ordinal');

                    log('old_pos ' + old_pos);
                    log('new_pos ' + new_pos);


                    model.set({
                        ordinal: new_pos
                    });
                    if(old_pos == new_pos){
                        //trigger associated events
                        this.sort();
                        return this;
                    }

                    var _this = this;
                    //update indexes of affected models
                    this.each(function(m){

                        //ordinal of current model in loop
                        var m_ordinal = m.get('ordinal');

                        //skip if this is the model we just updated
                        if(m.get('id') == m_id)
                            return;

                        if(old_pos < new_pos){
                            //moving down, ordinal is increasing

                            if(m_ordinal <= new_pos && !(m_ordinal <= 0)){
                                //this is in the range we care about
                                m.set({
                                    ordinal: m.get('ordinal') - 1
                                });

                            }

                        }else if(old_pos > new_pos){
                            //moving up, ordinal is decreasing                  
                             log('p1');

                            if(m_ordinal >= new_pos && !(m_ordinal >= (_this.length - 1))){
                                //this is in the range we care about
                                m.set({
                                    ordinal: m.get('ordinal') + 1
                                });

                            }

                        }

                    });

                    this.sort();                    
                    return this;

                }

编辑 4

发现另一个错误，修复它。

Backbone.Collection.prototype.move_to = function(m_id, new_pos) {

    //keep within range
    if(new_pos < 0)
        new_pos = 0;
    else if(new_pos > (this.length - 1))
        new_pos = this.length - 1;


    var model = this.get(m_id),
        old_pos = model.get('ordinal');

    log('old_pos ' + old_pos);
    log('new_pos ' + new_pos);

    model.set({
        ordinal: new_pos
    });
    if(old_pos == new_pos){
        //trigger associated events
        this.sort();
        return this;
    }

    var _this = this;
    //update indexes of affected models
    this.each(function(m){

        log(m.id);

        //ordinal of current model in loop
        var m_ordinal = m.get('ordinal');

        //skip if this is the model we just updated
        if(m.get('id') == m_id)
            return;

        if(old_pos < new_pos){
            //moving down, ordinal is increasing

            if(m_ordinal <= new_pos && m_ordinal >= old_pos && !(m_ordinal <= 0)){
                //this is in the range we care about
                m.set({
                    ordinal: m.get('ordinal') - 1
                }, {
                    silent: true
                });

            }

        }else if(old_pos > new_pos){
            //moving up, ordinal is decreasing                  
             log('p1');

            if(m_ordinal >= new_pos && m_ordinal <= old_pos && !(m_ordinal >= (_this.length - 1))){
                //this is in the range we care about
                m.set({
                    ordinal: m.get('ordinal') + 1
                }, {
                    silent: true
                });

            }

        }

    });

    this.sort();                    
    return this;
};

Answer 1

如果你查看 backbone.js 源代码，你会发现例如 add 方法支持将模型添加到某些索引

collectionName.add(model, {at: index});

从位置上移除可能需要您为集合创建一个自定义函数，例如:

// Your Collection

removeAt: function(options) {
  if (options.at) {
    this.remove(this.at(options.at));
  }
}

对于 +1/-1 你可以创建自定义函数并使用内置的下划线 indexOf 函数

// Your Collection

moveUp: function(model) { // I see move up as the -1
  var index = this.indexOf(model);
  if (index > 0) {
    this.remove(model, {silent: true}); // silence this to stop excess event triggers
    this.add(model, {at: index-1});
  }
}

moveDown: function(model) { // I see move up as the -1
  var index = this.indexOf(model);
  if (index < this.models.length) {
    this.remove(model, {silent: true}); // silence this to stop excess event triggers
    this.add(model, {at: index+1});
  }
}

通过这种方式，您还可以将 moveUp 和 moveDown 实现到模型本身，以获得更易于阅读的代码!

// Your Model

moveUp: function() {
  this.collection.moveUp(this);
}

// And the same for moveDown

但是现在索引属性没有保存在模型本身中。要读取索引，只需使用 collection.indexOf(model)，但如果您想始终将该信息存储在模型中，您可以绑定(bind)到 add 和 remove 事件以在对集合进行更改时更新所有索引:

// Your collection

initialize: function(options?) {
  ...
  this.on('add remove', this.updateModelOrdinals);
  ...
},

...

updateModelOrdinals: function() {
  this.each(function(model, index) {
    this.model.set('ordinal', index);
  });
}

等等!现在您应该拥有所需的功能，而无需重新发明轮子，并且仍然使用 Backbone 自己的功能保持 0 索引!抱歉让你有点失控，问问我是不是越过了你的脑袋。并阅读 the backbone.js source ，您可以在那里找到非常有用的东西!

希望这对您有所帮助!