如何使用 mongoose find() 在数组中查找指定对象属性的值

Question

My schema

{
_id: xxxxxxxxxxxxx,
totalCreatedForms: [
{formName: "formone", formIndex: 0},
{formName: "formtwo", formIndex: 1},
{formName: "formthree", formIndex: 2}
]
}

I used mongoose query to find the form I need as follows:

db.collection.find({"totalCreatedForms.formName":"formtwo"}, data=>{res.send(data)})

Is there a way, I can get the value of formIndex of the specified form. Here I am getting the whole data of the "_id", I have to filter again it in the front-end. But, I am wondering if there is a query to get the values of the specified form.

Answer 1

You need $ operator in this way:

db.collection.find({
  "totalCreatedForms.formName": "formtwo"
},
{
  "_id": 0,
  "totalCreatedForms.formIndex.$": 1
})

Find query has two objects.

The first to match the element you are looking for.

The second one is to indicate which fields returns. So, _id field will not be returned and, from array, only the index where the positional operator is placed, will be returned.

Ouput example is like this:

[
  {
    "totalCreatedForms": [
      {
        "formIndex": 1
      }
    ]
  }
]

Note that mongo is a data base who store documents and return documents, so this is the easiest way (without aggregation) to get only the value you want instead of the entire array.

Example here