Golang map containing both string and integer - json

Question

I am trying to create a JSON string from a map using JSON.Marshal() in golang. However, the int values are being displayed as strings surrounded by double quotes.
My code is outputting:
{ "age":
{
"$gt":"22",
"$lt":"20"
},
"location":
{
"$eq":"london"
},
"name":{
"$eq":"fred"
}
}
instead of
{ "age":
{
"$gt":22,
"$lt":20
},
"location":
{
"$eq":"london"
},
"name":{
"$eq":"fred"
}
}
I am using:
var output_map = map[string]map[string]string{}
//Populate map here
output_json, err := json.Marshal(output_map)
if err!= nil {
fmt.Println("Error encoding JSON")
}
fmt.Println(output_json)
My understanding is that JSON.Marshal() will print the integers correctly if they are supplied but my map won't contain integers. I could change my map to map[string]map[string]int{} but then it wouldn't contain the string values for 'name' and 'location'.
The ultimate problem is that I need the map to contain both int and string values. Some sort of map[string]map[string]{}.
How can I achieve this? Thank you in advance.
Harry

Answer 1

If you cannot describe your data with a properly typed struct then consider using a map with values of type interface{} (essentially any type):
output_map := map[string]map[string]interface{}{}
For example:
output_map := map[string]map[string]interface{}{
"age": {
"$gt": 18,
},
"location": {
"eq": "London",
},
}
bytes, err := json.MarshalIndent(&output_map, "", " ")
if err != nil {
panic(err)
}
// {
// "age": {
// "$gt": 18
// },
// "location": {
// "eq": "London"
// }
// }
Of course, using the interface{} type is not a best-practice; however, it's sometimes the only way to accomplish certain things.

Answer 2

We can declare variable for mix mapping with integer,string as below.
var variable_name = map[string]interface{}{}
e.g.
var variable_name = map[string]interface{}{
"name": c.String("name"),
"age": c.Int("age"),
}

Answer 3

I agree with maerics,
map[string]interface{} would be the way to go, if you have to avoid structs.
From your content I assume, that you are dealing with mongodb-queries.
So maybe the following code helps.
If you are going to query mongodb from go I would recommend the mgo-driver mgo.v2.
It implements a custom type bson.M which is the same as mentioned above, but works also for querying the db.
Beside this, it makes the code more readable.
Sample:
package main
import (
"fmt"
"gopkg.in/mgo.v2/bson"
"encoding/json"
)
func main() {
bsonMap := bson.M{
"age": bson.M{
"$gt": 22,
"$lt": 20,
},
"location": bson.M{"$eq": "london",},
"name": bson.M{"$eq": "fred"},
}
bytes, err := json.Marshal(bsonMap)
if err != nil {
panic(err)
}
fmt.Println(string(bytes))
}

Answer 4

Your code works as expected: map[string]map[string]string{} contains only string values, so json.Marshal(interface{}) return json string with marshaled string values.
I think you should use struct instead of map. Just create a struct, something like this:
type Age struct {
Gt int `json:"gt"`
Lt int `json:"lt"`
}
type Person struct {
Age Age `json:"age"`
Location string `json:"location"`
Name string `json:"name"`
}
And just marshal it with standart json.Marshal(interface{}) method.
(in this code json tags isn't required, but you can use it if you want to change names of fields in serialized json string)
I create test.go file with following code in main():
person := Person{
Age{
22,
20,
},
"London",
"Fred",
}
serialized, e := json.Marshal(person)
if e != nil {
fmt.Println(e)
return
}
fmt.Println(string(serialized))
and it returns this:
{
"age":
{
"gt":22,
"lt":20
},
"location":"London",
"name":"Fred"
}
P.S. I can't recommend you to use map[string]map[string]interface{} because in this case you need to have custom Unmarshaller (to fill up your map back). With structs you can unmarshal it by this way:
deserialized := Person{}
e = json.Unmarshal(serialized, &deserialized)
if e != nil {
fmt.Println("can't deserialize:", e)
return
}