如何使用mgo（golang客户端）查询mongodb中的UUID字段？

Question

I have problems with queries on UUID filed in my mongo collection. Mongo document structure is like:

{
    "_id": {
        "$oid": "5acf7faff5f02b0001e9fda1"
    },
    "j": {
        "$uuid": "d0459793-3ec0-71fd-319e-b959af081db6"
    },
    "s": "ok",
    "creation_date": {
        "$date": "2018-04-12T15:47:59.003Z"
    }
}

I want to get document, passing j uuid (not ObjectID). I create mongo connection, and I get my collection, then I try to execute this query:

import (    
       mgo "gopkg.in/mgo.v2"
       "gopkg.in/mgo.v2/bson"
)
...
var job *Job
uid, _ := uuid.FromString(m.ID)
e := c.Find(bson.M{"j": uid.String()}).One(&job)

but e is always equal to "not found".

m.ID is string of uuid without dashes- so I convert it to uuid.UUID.

Other queries like c.Find(bson.M{"s": "ok"}).All(&jobs) work fine, so I'm sure about connection & collection.

Using golang 1.11 & mongodb 3.6.

UPDATE:

When I do db.mycol.find() from mongo console result is a list of documents like:

{ "_id" : ObjectId("5acf5b0ac7fb0700010040ac"), "j" : BinData(3,"amOjUW1oQQ6dNsvLrQuDhg=="), "s" : "ok", "creation_date" : ISODate("2018-04-12T13:11:38.365Z") }

so I tried to modify my query like this:

e := c.Find(bson.M{"j": bson.Binary{0x03, []byte(m.ID)}}).One(&job)

And still it does not return the document.

Answer 1

The j property in your MongoDB documents is of type BinData type 3, so using a filter where you match it against a string will never yield any results.

Your second attempt is on the right track. Except that you are filtering for the UTF-8 byte sequences of the hex representation of the UUID string (this is how Go stores strings in memory, this is what a string -> []byte conversion yields). This again will never yield any results.

And the reason is that the binary data you have to provide in bson.Binary is not the above mentioned value, but the raw bytes of the UUID.

So what you have to do is hex-decode the UUID (which is given to you as the hex representation), and use this binary data.

data, err := hex.DecodeString(m.ID)
if err != nil {
    panic(err)
}

e := c.Find(bson.M{"j": bson.Binary{
    Kind: bson.BinaryUUIDOld,
    Data: data,
}}).One(&job)

Note that you have to pass the UUID to hex.DecodeString() without dashes, so you don't even need any 3rd party libs to process the UUID strings you have.

Also please note that gopkg.in/mgo.v2 is not maintained anymore. Instead use the community supported fork: github.com/globalsign/mgo.