Fill struct dynamically from parameters - json

Question

I've the following struct which works as expected Im getting
data and I was able
type Service struct {
Resources []struct {
Model struct {
Name string `json:"name"`
Credentials struct {
path string `json:"path"`
Vts struct {
user string `json:"user"`
id string `json:"id"`
address string `json:"address"`
} `json:"vts"`
} `json:"credentials"`
} `json:"model"`
} `json:"resources"`
}
service:= Service{}
err := json.Unmarshal([]byte(data), &service
The data is like following,
service1
{
"resources": [
"model": {
"name": "cred",
"credentials": {
"path": "path in fs",
"vts": {
"user": "stephane",
"id": "123",
"address": "some address"
}
},
}
},
Now some services providing additional data under vts for example now we have 3 fields (user/id/address) but some services (service1) can provides additional data like email, secondName ,etc . but the big problem here is that
I need to get it from parameters since (service 2) education, salary etc
Service2
{
"resources": [
"model": {
"name": "cred",
"credentials": {
"path": "path in fs",
"vts": {
"user": "stephane",
"id": "123",
"address": "some address",
"email" : "some email",
"secondName" : "secondName"
}
},
}
},
service N
{
"resources": [
"model": {
"name": "cred",
"credentials": {
"path": "path in fs",
"vts": {
"user": "stephane",
"id": "123",
"address": "some address",
"salary" : "1000000"
}
},
}
},
Of course If I know in advance the fields I can put them all in the struct and use omitempty but I dont know, I just get it as parameter to the function (the new properties names) , some service can provide 10 more fields in this struct (which I should get the properties name of them as args[]to the functions) but I don't know them in advance, this should be dynamic somehow ....is there a nice way to handle it in Golang ?

Answer 1

If you don't know the fields in advance, then don't use a struct but something that is also "dynamic": a map.
type Service struct {
Resources []struct {
Model struct {
Name string `json:"name"`
Credentials struct {
Path string `json:"path"`
Vts map[string]interface{} `json:"vts"`
} `json:"credentials"`
} `json:"model"`
} `json:"resources"`
}
map[sting]interface{} can hold values of any type. If you know all fields will hold a string value, you may also use a map[string]string so it will be easier to work with it.
Example with input JSON:
{
"resources": [
{
"model": {
"name": "cred",
"credentials": {
"path": "path in fs",
"vts": {
"user": "stephane",
"id": "123",
"address": "some address",
"dyn1": "d1value",
"dyn2": "d2value"
}
}
}
}
]
}
Testing it:
service := Service{}
err := json.Unmarshal([]byte(data), &service)
fmt.Printf("%q %v", service, err)
Output (try it on the Go Playground):
{[{{"cred" {"path in fs" map["dyn2":"d2value" "user":"stephane" "id":"123"
"address":"some address" "dyn1":"d1value"]}}}]} <nil>
Now if you want to collect values from the Vts map for a set of keys, this is how you can do it:
args := []string{"dyn1", "dyn2"}
values := make([]interface{}, len(args))
for i, arg := range args {
values[i] = service.Resources[0].Model.Credentials.Vts[arg]
}
fmt.Println(values)
Output of the above will be (try it on the Go Playground):
[d1value d2value]