How to retrieve value from map - go lang?

I am working with mgo to use MongoDB with Go. I have the following code:

func Find(collectionName, dbName string, query interface{}) (result []interface{}, err error) {
	collection := session.DB(dbName).C(collectionName)
	err = collection.Find(query).All(&result)
	return result, err
}

func GetTransactionID() (id interface{}, err error) {
	query := bson.M{}
	transId, err := Find("transactionId", dbName, query)
	for key, value := range transId {
		fmt.Println("k:", key, "v:", value)
	}
}

Output: k: 0 v: map[_id:ObjectIdHex("536887c199b6d0510964c35b") transId:A000000000]

I need to get the values of _id and transId from the map value returned in the slice from Find. How can I do that?

I'm just guessing but in case you just want to retrieve all Transaction documents and print them - here is how:

Given you have a struct representing the structure of the documents of your collection e.g.:

type Transaction struct {
  Id            bson.ObjectId `bson:"_id"`
  TransactionId string        `bson:"transId"`
}

You can obtain all the documents using the MongoDB driver (mgo):

var transactions []Transaction
err = c.Find(bson.M{}).All(&transactions)
// handle err
for index, transaction := range transactions {
  fmt.Printf("%d: %+v\n", index, transaction)
}

Addition (generic solution)

OK, after you provided some more insight this might be a generic solution without using a struct. Try to marshall into a BSON document bson.M (not tested):

var data []bson.M
err := c.Find(bson.M{}).All(&data)
// handle err 
for _, doc := range data {
  for key, value := range doc {
    fmt.Println(key, value)
  }
}