CODEWITHSUNDEEP
jsongostruct
Saif Abid
Saif Abid

Reputation: 559

Capitals in struct fields

I'm using this library to access CouchDB (cloudant to be specific) "github.com/mikebell-org/go-couchdb" and I've noticed a problem.

When I go to add a file to the database and pass in a struct, only the fields of the struct which started with a capital letter get added.

For example 

type Person struct {
    name string
    Age  int
}

func main() {
    db, _ := couchdb.Database(host, database, username, password)
    joe := Person{
        name: "mike",
        Age:  190,
    }
    m, _ := db.PostDocument(joe)
}

In this case, only the "age" field got updated and inserted into my database.

I've noticed this problem in another case also - when I'm doing something like this : 

type Sample struct {
    Name string
    age  int 
}


joe := Sample{
    Name: "xx",
    age:  23,
}

byt, _ := json.Marshal(joe)

post_data := strings.NewReader(string(byt))
fmt.Println(post_data)

in this case, only Name would be printed out : 

output : &{{"Name":"xx"} 0 -1}

Why is this? and If I would like to have a field with a lowercase and be inside the database, is that possible?

Upvotes: 54

Views: 37125

Answers (3)

Khanbala Rashidov
Khanbala Rashidov

Reputation: 102

json.Marshal method struct-in field-i only accepts fields that start with a capital letter

The json package only accesses the exported fields of struct types (those that begin with an uppercase letter). Therefore only the exported fields of a struct will be present in the JSON output.

type Sample struct {
    Name string
    Age  int 
}

Upvotes: 1

chendesheng
chendesheng

Reputation: 2129

json package only stringfiy fields start with capital letter. see http://golang.org/pkg/encoding/json/

Struct values encode as JSON objects. Each exported struct field becomes a member of the object, using the field name as the object key, unless the field is omitted for one of the reasons given below.

You need define the struct like this:

type Sample struct{
    Name string `json:"name"`
    Age int `json:"age"`
}

Upvotes: 7

julienc
julienc

Reputation: 20325

This is because only fields starting with a capital letter are exported, or in other words visible outside the curent package (and in the json package in this case).

Here is the part of the specifications refering to this: http://golang.org/ref/spec#Exported_identifiers

Still, you can unmarshall json fields that do no start with a capital letters using what is called "tags". With the json package, this is the syntax to use:

type Sample struct {
    Name string `json:"name"`
    Age  int    `json:"age"`
}

Refer to the documentation for more information about this.

Upvotes: 88

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