Question

我有两本书籍和作者。当我在这些集合之间进行查找时，我得到了所需的结果，但我需要重命名＆＃34; _id＆＃34;到＆＃34; id＆＃34;。当我重命名这些字段时，作者＆＃34; _id＆＃34;正在被书籍取代＆＃34; _id＆＃34;而不是作者＆＃34; _id＆＃34;。请看下面的

Error in ets(object, lambda = lambda, allow.multiplicative.trend =  allow.multiplicative.trend,  : 
  y should be a univariate time series
Additional: Warnings:
1: In ets(x, "ANN", alpha = alpha, opt.crit = "mse", lambda = lambda,  :
  Missing values encountered. Using longest contiguous portion of time series
2: In fit$call <- match.call() : ...

结果：

  Book.collection.aggregate([
  {'$lookup' => {'from' => "authors",'
                localField' => "_id",
                'foreignField' => "book_id",
                'as' => "authors"}}
  ])

我尝试将_id字段重命名为id

{
  "_id": 1,
  "title": "abc123",
  "isbn": "0001122223334",
  "copies": 5,
  "updated_at": "2018-03-02T09:17:24.546Z",
  "created_at": "2018-03-02T09:17:24.546Z",
  "authors": [
    {
      "_id": 10,
      "first": "a",
      "last": "a",
      "book_id": 1,
      "updated_at": "2018-03-02T09:22:07.115Z",
      "created_at": "2018-03-02T09:22:07.115Z"
    }
  ]
}

在上述＆＃34;项目＆＃34;如果我说

Book.collection.aggregate([
  {'$lookup' => {'from' => "authors",
                'localField' => "_id",
                'foreignField' => "book_id",
                'as' => "authors"}},
  {'$project' => {'id' => '$_id', '_id' => 0, 'title' => 1, "isbn" => 1, "copies" => 1,  "updated_at" => 1, 
                  "authors" => { 'id' => '$_id', 'first' => 1, 'last' => 1, 'book_id' => 1, 'updated_at' => 1}}}

  ])

然后结果是

"authors" => { 'id' => '$_id'

作者的身份是＆＃34; 1＆＃34;，而那应该是＆＃34; 10＆＃34;。请建议我如何进行更改

Answer 1

试试这个，只需展开并在项目管道中提供此if( isset($_GET['action']) ) { $action= $_GET['action']; // $action=''; //Just remove this code }

$authors._id

Answer 2

您可以$unwind作者，项目ID，然后分组，或使用$map单独重塑作者。我相信后者应该表现得更好，但是当你硬编码作者的字段时，它的灵活性会稍微提高一些：

Book.collection.aggregate([
{$addFields: {id:"$_id", "authors": {$map:{
    input: "$authors",
    as: "a",
    in: {
      "id": "$$a._id",
      "first": "$$a.first",
      "last": "$$a.last",
      "book_id": "$$a.book_id",
      "updated_at": "$$a.updated_at",
      "created_at": "$$a.created_at"
    }
}}}},
{$project: {_id:0}}
])

mongodb 3.2.6：$ lookup和$ project使用mongoid重命名_id字段

2 个答案: