unstructred inner document with mgo - mongodb

Question

I have a document which has this following structure
{ "_id" : "736722976", "value" : { "total_visit" : 4, "FIFA World Cup 2014" : 1, "Germany" : 1, "Algeria" : 1, "Thomas Muller" : 1, "Mesut Ozil" : 1, "Monsoon" : 1, "India Meteorological Department (IMD)" : 1, "Web Exclusive" : 2, "Specials" : 1, "Tapas Pal" : 1, "Twitter Trends" : 1, "Sunanda Pushkar" : 1, "Shashi Tharoor" : 1, "AIIMS" : 1, "special" : 1 } }
THE MOST IMPORTANT thing is that the sub document structure under the key "value" is variable so I can not create a structure for that. I tried to follow the suggestion here - Unstructured MongoDB collections with mgo
And I came with this code ---
package main
import ("fmt"
"labix.org/v2/mgo" //importing mgo
"labix.org/v2/mgo/bson"
_ "reflect"
)
type AnalysisStruct struct{
Id string `bson:"_id,omitempty"`
Value bson.M `bson:",inline"`
}
func main() {
var m AnalysisStruct
//connecting to localhost mongodb
session, err := mgo.Dial("localhost")
if err != nil {
panic(err)
}
defer session.Close()
c := session.DB("my_analysis_db").C("analysis_mid_2")
iter := c.Find(nil).Iter()
for{
if iter.Next(&m){
fmt.Println(m.Value["value"]["total_visit"])
}else{
break
}
}
}
When I try to build this using go build -v -o analyzer it shows me this error---
./analyzer.go:32: invalid operation: m.Value["value"]["total_visit"] (index of type interface {})
I am terribly stuck with this. Can not get anything going. Please can somebody help?
Thanks
I cam up with this code after doing some research. Not the most optimized one for sure. But for my case it works. Took help from
http://blog.denevell.org/golang-interface-type-assertions-switch.html
https://groups.google.com/forum/#!topic/mgo-users/JYE-CP15az4
package main
import ("fmt"
"labix.org/v2/mgo" //importing mgo
"labix.org/v2/mgo/bson"
_ "reflect"
)
type AnalysisStruct struct{
Id string `bson:"_id,omitempty"`
Value bson.M `bson:",inline"`
}
func main() {
var m AnalysisStruct
//connecting to localhost mongodb
session, err := mgo.Dial("localhost")
if err != nil {
panic(err)
}
defer session.Close()
c := session.DB("consumergenepool_db").C("analysis_mid_2")
iter := c.Find(nil).Iter()
for{
if iter.Next(&m){
s := m.Value["value"].(bson.M)
data, _ := bson.Marshal(s)
var m bson.M
_ = bson.Unmarshal(data, &m)
fmt.Println(m)
for k, v := range m{
fmt.Print(k)
fmt.Print(" :: ")
fmt.Println(v)
}
}else{
break
}
}
}
Let me know your thoughts on this.
Thanks

Answer 1

When testing something new always use a lot of fmt.Printf's to get a feel for it, that being said.
Value bson.M `bson:",inline"`
Should be
Value bson.M `bson:"value,omitempty"`
And
fmt.Println(m.Value["value"]["total_visit"])
Should be:
fmt.Printf("%#v\n", m)
fmt.Println(m.Value["total_visit"])
Your m.Value is "value", so you can use m.Value["total_visit"] directly.
playground
//edit
You can only use inline to catch any fields that that aren't a part of the original struct, but since your struct only has 2 fields (Id and Value), you don't need it.
Now if you were to keep ,inline you would use it like this:
if v, ok := m.Value["value"].(bson.M); ok {
fmt.Println(v["total_visit"])
}
Because m.Value["value"] is an interface{}, you have to type assert it back to it's original value, bson.M before you could use it.