Updating entity in Google Appengine datastore with Go

I am toying with GAE, Go and the datastore. I have the following structs:

type Coinflip struct {                                                                                                                                                                                                                      
  Participants []*datastore.Key
  Head         string
  Tail         string
  Done         bool
}

type Participant struct {
  Email string
  Seen  datastore.Time
}

(For those wondering I store Participants as a slice off Key pointers because Go doesn't automatically dereferences entities.)

Now I want to find a Participant with a particular Email address associated with a know Coinflip. Like so (this works):

coinflip, _ := find(key_as_string, context)
participants, _ := coinflip.fetchParticipants(context) /* a slice of Participant*/

var found *Participant
for i := 0; i < len(participants) && found == nil; i++ {
  if participants[i].Email == r.FormValue("email") {
    found = &participants[i]
  }
}
(*found).Seen = datastore.SecondsToTime(time.Seconds())

How do I save *found to the datastore? I need the key apparently but the coupling between the Participant struct and the Key is very loose.

I'm unsure how to proceed from here. Do I need to return the keys as well from the fetchParticipants call? The Java and Python GAE implementation seem quite a bit simpler (just call put() on the object).

Thanks in advance,

> Do I need to return the keys as well from the fetchParticipants call?

Yes. And then call "func Put(c appengine.Context, key *Key, src interface{}) (*Key, os.Error)"

> The Java and Python GAE implementation seem quite a bit simpler (just
> call put() on the object).

Probably a fair statement. The Go community has a very strong bias against "magic". In this case the Participant struct has two fields that you have declared. Adding the key to it in the background would be considered magic.

For interacting with data in Go, consider using our new library https://github.com/matryer/gae-records for an Active Record, data objects wrapper around the datastore. It sorts out a lot of the hassle for you.

For example, it supports:

// create a new model for 'People'
People := gaerecords.NewModel("People")

// create a new person
mat := People.New()
mat.
 SetString("name", "Mat")
 SetInt64("age", 28)
 .Put()

// load person with ID 1
person, _ := People.Find(1)

// change some fields
person.SetInt64("age", 29).Put()

// load all People
peeps, _ := People.FindAll()

// delete mat
mat.Delete()

// delete user with ID 2
People.Delete(2)

// find the first three People by passing a func(*datastore.Query)
// to the FindByQuery method
firstThree, _ := People.FindByQuery(func(q *datastore.Query){
  q.Limit(3)
})

// build your own query and use that
var ageQuery *datastore.Query = People.NewQuery().
  Limit(3).Order("-age")

// use FindByQuery with a query object
oldestThreePeople, _ := People.FindByQuery(ageQuery)

// using events, make sure 'People' records always get
// an 'updatedAt' value set before being put (created and updated)
People.BeforePut.On(func(c *gaerecords.EventContext){
  person := c.Args[0].(*Record)
  person.SetTime("updatedAt", datastore.SecondsToTime(time.Seconds()))
})