如何使用Go将密钥存储在数据存储对象中？

Question

I'm trying to put a *Key of a Location

type Location struct 
    City, State, Country string
}

in a Band

type Band struct {
    Name string
    LocationId *datastore.Key
    Albums []Album
}

When I first create a Location, add the key, then try to retrieve the Location values, the strings all come out empty. If I then add a new Band, the location I created shows up fine, and using that location in a new Band works. I'm using incomplete keys:

func AddLocation(value Location, rq *http.Request) (*datastore.Key, error) {
    c := appengine.NewContext(rq)
    key := datastore.NewIncompleteKey(c, config.LOCATION_TYPE, nil)
    _, err := datastore.Put(c, key, &value)

    return key, err
}

Using an existing Location is as follows:

case "existing":
    rawId := rq.FormValue("location_id")
    q := strings.Split(rawId, ",")
    x := q[1]
    id_int, e := strconv.ParseInt(x, 10, 64)
    if e != nil {
        message = e.Error()
    }
    locationId = datastore.NewKey(c, config.LOCATION_TYPE, "", id_int, nil)
    //  message = "not implemented yet"
    break

Using the key from the original Put didn't seem to work, so I resorted to:

case "new":
    location := model.Location{rq.FormValue("city"), rq.FormValue("state"), rq.FormValue("country")}
    var err error
    _, err = model.AddLocation(location, rq)
    if err != nil {
        message = "Location add: " + err.Error()
    }
    q := datastore.NewQuery(config.LOCATION_TYPE).Filter("City =", location.City).
        Filter("State =", location.State).Filter("Country =", location.Country).
        KeysOnly()
    keys, err := q.GetAll(c, nil)
    if err != nil {
    message = "Location add: " + err.Error()
    }
    var k *datastore.Key
    for _, key := range keys {
        k = key
        break
    }
    locationId = k
    break

And that didn't work right either. What am I not getting?

Answer 1

When you call datastore.Put with an incomplete key, the key's id is not filled in. The returned key has it. You're ignoring the return value from datastore.Put with _.

Your AddLocation func should look like this:

func AddLocation(value Location, rq *http.Request) (*datastore.Key, error) {
    c := appengine.NewContext(rq)
    key := datastore.NewIncompleteKey(c, config.LOCATION_TYPE, nil)
    // this line updates the key with accurate information
    key, err := datastore.Put(c, key, &value)

    return key, err
}