使用Go更新Google Appengine数据存储区中的实体

Question

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,

Answer 1

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()))
})