数组中的对象的特征值提取生成新对象实现方法

最近要做一个可视化的SQL语句生成功能视图，

项目中遇到一个JSON保存后还原的问题，由于保存之前和后台沟通约定好保存的JSON格式，所以在还原的时候，就要按照保存的格式来进行逆向解析。

首先来看一下保存的JSON内容

var oldObj= [
      {
        "fieldName": "上班时间1",
        "fieldId": "working_hours_1",
        "fieldType": "time",
        "parentTableId": "class_table",
        "parentTableName": "班别表",
        "order": 0,
        "checked": false
      },
      {
        "fieldName": "下班时间1",
        "fieldId": "off_hours_1",
        "fieldType": "time",
        "parentTableId": "class_table",
        "parentTableName": "班别表",
        "order": 0,
        "checked": false
      },
      {
        "fieldName": "上班时间2",
        "fieldId": "working_hours_2",
        "fieldType": "time",
        "parentTableId": "class_table",
        "parentTableName": "班别表",
        "order": 0,
        "checked": false
      },
      {
        "fieldName": "下班时间2",
        "fieldId": "off_hours_2",
        "fieldType": "time",
        "parentTableId": "class_table",
        "parentTableName": "班别表",
        "order": 0,
        "checked": false
      },
      {
        "fieldName": "姓名",
        "fieldId": "name",
        "fieldType": "text",
        "parentTableId": "punch_card_record",
        "parentTableName": "打卡记录",
        "order": 0,
        "checked": false
      },
      {
        "fieldName": "工号",
        "fieldId": "job_number",
        "fieldType": "text",
        "parentTableId": "punch_card_record",
        "parentTableName": "打卡记录",
        "order": 0,
        "checked": false
      },
      {
        "fieldName": "打卡时间",
        "fieldId": "punch_time",
        "fieldType": "datetime",
        "parentTableId": "punch_card_record",
        "parentTableName": "打卡记录",
        "order": 0,
        "checked": false
      }
    ],

注：请忽略对象中的order，checked字段。

我们姑且将oldObj数组中的每个obj称之为字段, 可以看到字段的 parentTableId 是有出现重复的情况的，

而我们要将这个数组解析成一个以 parentTableId 为特征值的新对象。

var newObj = [
    {
        "parentFormId": "class_table",
        "parentFormName": "班别表",
        "fields": [
            {
                "fieldName": "上班时间1",
                "fieldId": "working_hours_1",
                "fieldType": "time",
                "parentTableId": "class_table",
                "parentTableName": "班别表",
                "order": 0,
                "checked": false
            },
            {
                "fieldName": "下班时间1",
                "fieldId": "off_hours_1",
                "fieldType": "time",
                "parentTableId": "class_table",
                "parentTableName": "班别表",
                "order": 0,
                "checked": false
            },
            {
                "fieldName": "上班时间2",
                "fieldId": "working_hours_2",
                "fieldType": "time",
                "parentTableId": "class_table",
                "parentTableName": "班别表",
                "order": 0,
                "checked": false
            },
            {
                "fieldName": "下班时间2",
                "fieldId": "off_hours_2",
                "fieldType": "time",
                "parentTableId": "class_table",
                "parentTableName": "班别表",
                "order": 0,
                "checked": false
            }
        ]
    },
    {
        "parentFormId": "punch_card_record",
        "parentFormName": "打卡记录",
        "fields": [
            {
                "fieldName": "姓名",
                "fieldId": "name",
                "fieldType": "text",
                "parentTableId": "punch_card_record",
                "parentTableName": "打卡记录",
                "order": 0,
                "checked": false
            },
            {
                "fieldName": "工号",
                "fieldId": "job_number",
                "fieldType": "text",
                "parentTableId": "punch_card_record",
                "parentTableName": "打卡记录",
                "order": 0,
                "checked": false
            },
            {
                "fieldName": "打卡时间",
                "fieldId": "punch_time",
                "fieldType": "datetime",
                "parentTableId": "punch_card_record",
                "parentTableName": "打卡记录",
                "order": 0,
                "checked": false
            }
        ]
    }
]

注：请忽略新对象中的 parentTableId，parentTableName，order，checked 字段, 因为不影响我们的目的，为了方便直接就把对象push进去了。

可以看到，新数组对象中，将字段中的parentTable的ID，Name都提取了出来，并且将这些字段push到了一个newObj数组里面。
那么这个实现的结果，是怎么达成的呢，且看一下代码：

//新建一个用于存放特征值的数组
let parentTableIdArray = [];
//遍历旧数组对象
for(let item of oldObj){
//获取当前的对象parentTableId是否存在特征值数组
  let index = parentTableIdArray.indexOf(item.parentTableId)
//当前的对象parentTableId不存在特征值数组时
  if(index == -1){
//将当前的对象parentTableId加入到特征值数组
    parentFormIdArray.push(item.parentTableId)
//生成新对象
    let obj = {
      fields: [],
      parentFormId: item.parentTableId,
      parentFormName: item.parentTableName
    }
    obj.fields.push(item);
//插入新生成的对象
    this.newObj.push(obj);
  }
//当前的对象parentTableId存在特征值数组时
  else{
//在当前的对象parentTableId的位置插入新对象
    this.newObj[index]['fields'].push(item);
  }
}   

这个方法可以有效的提取数组内的对象特征值。如果需要多次调用，可以考虑封装。