在mongodb文档中找到一个子文档

How can I retrieve only the subdocument in a mongodb document?

如何只检索mongodb文档中的子文档？

 const result = await context.parents.find(
    {
      _id: mongoose.Types.ObjectId(args.parentId),
      children: {
        $elemMatch: {
          _id: mongoose.Types.ObjectId(args.childId),
        }
      }
    },
    {
      _id: 0,
      'children.$': 1
    });

To access to the subdocument I need to do this:

要访问子文档，我需要这样做：

  if (result) {
    return result[0].toObject().children[0];
  }

Here is the document schema:

这是文档架构：

const ParentSchema = new mongoose.Schema({
    firstName: { type: mString, required: true, trim: true },
    lastName: { type: mString, required: true, trim: true },
    birthdate: mDate,
    created: { type: mDate, required: true, default: Date.now },
    children: [{
        startDate: { type: mDate, required: true }
    }],
});

Is there a way to return directly the only child found?

有没有办法直接返回找到的唯一孩子？

1 个解决方案

#1

You can try below aggregation query.

您可以尝试以下聚合查询。

$match to only consider documents where there is atleast one element in array matching input criteria.

$ match只考虑匹配输入条件的数组中至少有一个元素的文档。

$filter array on the input criteria and $arrayElemAt to project the single matched element.

$ filter数组在输入条件上，$ arrayElemAt用于投影单个匹配元素。

context.parents.aggregate([
 {"$match":{
    _id: mongoose.Types.ObjectId(args.parentId),
    "children._id":mongoose.Types.ObjectId(args.childId)
 }},
 {"$project":{
    "_id":0, 
    "children":{
       "$arrayElemAt":[
          {"$filter":{
            "input":"$children",
            "as":"child",
            "cond":{"$eq":["$$child._id",mongoose.Types.ObjectId(args.childId)]}
          }},
       0]
    }
 }}
])

#1