Mongo retrieve all values of a specific field including duplicates as list

I have the following data which I am querying on:

   [
      {
        "_id": 1,
        "domainName": "test1.com",
        "hosting": "hostgator.com",
        "to": "nanjing",
        "travelDate": "09/06/2022",
        "trainNumber": 123
      },
      {
        "_id": 2,
        "domainName": "test2.com",
        "hosting": "aws.amazon.com",
        "to": "beijing",
        "travelDate": "09/02/2022",
        "trainNumber": 123
      },
      {
        "_id": 3,
        "domainName": "test3.com",
        "hosting": "aws.amazon.com"
      },
      {
        "_id": 4,
        "domainName": "test4.com",
        "hosting": "hostgator.com",
        "to": "shanghai",
        "travelDate": "09/06/2022",
        "trainNumber": 1234
      },
      {
        "_id": 5,
        "domainName": "test5.com",
        "hosting": "aws.amazon.com",
        "to": "wuhan",
        "travelDate": "09/06/2022",
        "trainNumber": 1234
      },
      {
        "_id": 6,
        "domainName": "test6.com",
        "hosting": "cloud.google.com",
        "to": "nanjing",
        "travelDate": "09/06/2022",
        "trainNumber": 123
      },
      {
        "_id": 7,
        "domainName": "test7.com",
        "hosting": "aws.amazon.com",
        "to": "nanjing",
        "travelDate": "09/02/2022",
        "trainNumber": 123
      },
      {
        "_id": 8,
        "domainName": "test8.com",
        "hosting": "hostgator.com",
        "to": "nanjing",
        "travelDate": "09/02/2022",
        "trainNumber": 123
      },
      {
        "_id": 9,
        "domainName": "test9.com",
        "hosting": "cloud.google.com",
        "to": "nanjing",
        "travelDate": "09/02/2022",
        "trainNumber": 123
      },
      {
        "_id": 10,
        "domainName": "test10.com",
        "hosting": "godaddy.com",
        "to": "nanjing",
        "travelDate": "09/02/2022",
        "trainNumber": 123
      }
    ]

I am using the following query to get the filed to as a list of string

db.collection.aggregate({
  $match: {
    travelDate: {
      $eq: "09/06/2022"
    },
    trainNumber: {
      $eq: 1234
    }
  }
},
{
  $group: {
    _id: "",
    destStations: {
      $push: "$to"
    }
  }
},
{
  $project: {
    _id: 0
  }
})

The above query returns the following result as expected:

[
  {
    "destStations": [
      "shanghai",
      "wuhan"
    ]
  }
]

But when I am trying to convert it using the following spring mongo aggregation I cannot get the appropriate result. Can anyone help?

        Aggregation agg = newAggregation(                match(Criteria.where("travelDate").is(travelDate).and("trainNumber").is(trainNumber)),
                group("id").push("to").as("destStations"),
                project().andExclude("id")
        );

You are grouping by id, in your spring mongo aggregation, but in your query it's you are grouping on "" empty string. That's why the results might be varying.

Try passing no argument to group function, like this:

Aggregation agg = newAggregation(match(Criteria.where("travelDate").is(travelDate).and("trainNumber").is(trainNumber)),
                group().push("to").as("destStations"),
                project().andExclude("id")
        );