Go mgo不存储对象

Question

Using mgo I'm unable to store any meaningful data. Only the _id gets stored

type Person struct {
    name string
    age int
}

func main() {
    session, err := mgo.Dial("localhost")
    if err != nil {
        log.Fatal(err)
    }
    defer session.Close()

    p := Person{"Joe", 50}
    ppl := session.DB("rest").C("people")
    ppl.Insert(p)
}

The result in Mongo is just the _id field - no sign of "Joe".

---

Using go 1.1.2 on Arch linux, MongoDB 2.4.6.

Answer 1

type Person struct {
    name string
    age  int
}

The mgo package can't access unexported (lowercase) fields of your struct (i.e. no other package than the one the struct is defined in can). You need to export them (first letter must be upper case), like this:

type Person struct {
    Name string 
    Age  int    
}

If you wish to have the field names in lower case in the DB you must provide a struct tag for them, like this:

type Person struct {
    Name string `bson:"name"`
    Age  int    `bson:"age"`
}

See the documentation on names:

Names are as important in Go as in any other language. They even have semantic effect: the visibility of a name outside a package is determined by whether its first character is upper case. [...]

EDIT:

Gustavo Niemeyer (author of the mgo and bson packages) noted in the comments that unlike the json package, the bson marshaller will lowercase all struct field names when commiting to the database, effectively making the last step in this answer superfluous.