如何从MongoDb查询中编写go bson.M

Question

I am using mongodb as database. I'm able to query the database from the command line using the command

db.nfinstances.distinct("ipv4Addresses",{"nfType":"AMF", "amfInfo.amfSetId": "3fa85f64-5717-4562-b3fc-2c963f66af33"})

and this give me the ip address [x.x.x.x] output that I want.

However, if I query using the golang query

var SliceIP []NfInstance

db.C(COLLECTION).Find(bson.M{
                      "nfType": "AMF",
                      "amfInfo.amfSetId": "3fa85f64-5717-4562-b3fc-2c963f66af33"}
                      ).Distinct("ipv4Addresses", &SliceIP)

I'm getting an empty array instead of the the IP address string in an array. In the database i have the json document as

{
    "nfinstanceID": "3fa85f64-5717-4562-b3fc-2c963f66af33",
    "nfType": [
        "AMF"
    ],
    "nfStatus": [
        "REGISTERED"
    ],
    "sNssais": [
        {
            "sst": 1,
            "sd": "sd1"
        }
    ],
    "nsiList": [
        "string"
    ],
    "ipv4Addresses": [
        "198.51.100.300"
    ],
    "allowedNssais": [
        {
            "sst": 1,
            "sd": "sd1"
        }
    ],
    "amfInfo": {
        "amfSetId": "3fa85f64-5717-4562-b3fc-2c963f66af33",
        "taiList": [
            {
                "plmnId": {
                    "mcc": "244",
                    "mnc": "38"
                },
                "tac": "string"
            }
        ],
        "n2InterfaceAmfInfo": {
            "ipv4EndpointAddress": [
                "198.51.100.105"
            ]
        }
    }
}

Mongodb command line query look like this

> db.nfinstances.distinct("ipv4Addresses",{"nfType":"AMF", "amfInfo.amfSetId": "3fa85f64-5717-4562-b3fc-2c963f66af33"})

mongodb Output:

[ "198.51.100.300" ]

The same output I am expecting using the bson.M

Can anyone help find the problem?

Answer 1

Query.Distinct() unmarshals the list of distinct values, not complete documents (the equivalent MongoDB query also returns values, not documents).

So simply unmarshal the distinct IPs into a value of type []string (and also never forget about handling errors):

var ips []string

err := db.C(COLLECTION).Find(bson.M{
    "nfType":           "AMF",
    "amfInfo.amfSetId": "3fa85f64-5717-4562-b3fc-2c963f66af33",
}).Distinct("ipv4Addresses", &ips)
if err != nil {
    // handle error
}