Javascript LEFT OUTER JOIN查询结果的转换

Question

我正在使用 node-postgres 检索 LEFT OUTER 连接查询的结果：

SELECT S.SEASON_ID, S.SEASON_NAME, I.ITEM_NAME, I.NOTE FROM T_SEASON S LEFT OUTER JOIN T_ITEM I ON S.SEASON_ID = I.SEASON_ID;

结果集将如下所示：

[
 {
   season_id:1, 
   season_name: "season 1", 
   item_name:"item1", 
   item_note: "text"
 }, 
 {
   season_id:1, 
   season_name: "season 1", 
   item_name:"item2", 
   item_note: "text"
 }, 
 {
   season_id:2, 
   season_name: "season 2", 
   item_name:"item3", 
   item_note: "text"
 }
]

我需要做的是将其分解为 "season" 个对象的数组，如下所示：

[
 {
   seasonId: 1, 
   season_name: "season 1", 
   items: [
      {item_name: "item1", item_note: "text"},
      {item_name: "item2", item_note: "text"}
   ]
 }, 
 {
   seasonId: 2, 
   season_name: "season2", 
   items: [
      {item_name: "item3", item_note: "text"}
   ]
 }
]

换句话说，"item" 是季节对象的子集合。

我正在寻找执行此操作的最简单方法。我可以使用 Lodash。

Answer 1

您可以使用reduce

根据season_id创建密钥。检查键是否存在，而不是在该特定键的项目中推送值，如果不存在，则创建具有适当值的新键。最后只需从对象中取出值即可获得所需的输出。

let data = [{season_id:1, season_name: "season 1", item_name:"item1", item_note: "text"}, {season_id:1, season_name: "season 1", item_name:"item2", item_note: "text"}, {season_id:2, season_name: "season 2", item_name:"item3", item_note: "text"}]

let output = data.reduce(( op, {season_id, item_name, item_note, season_name }) => {
  if(op[season_id]){
    op[season_id].items.push({item_name,item_note})
  } else {
    op[season_id] = {
      season_id,
      season_name,
      items: [{item_name,item_note}]
    }
  }
  return op
},{})

console.log(Object.values(output))

Javascript LEFT OUTER JOIN查询结果的转换

Javascript Conversion of LEFT OUTER JOIN Query Result

javascript

node-postgres