"datastore: dst has invalid type"

[Tomi Hiltunen]

Hi,

I'm trying to load a bunch of Debate structs from the GAE datastore using the GetMulti function. Datastore can perform the simple Get for the individual entities with the same keys. For the GetMulti I get an error message saying "datastore: dst has invalid type".

var debates []Debate

if err := datastore.GetMulti(c, debateKeys, &debates); err != nil {

return nil, err

}

The Debate struct looks like this:

type Debate struct {

// General

Id string

Topic string

Creator int64

Type int64

CustomPositive string

CustomNegative string

// Status

Status int64

CreatedAt time.Time

UpdatedAt time.Time

ClosedAt time.Time

// Participants

Participants int64

// Arguments

Arguments []Argument

}

I suspect it has to do with the list of Argument type structs nested inside. Though, all the Arguments contain only properties supported by the datastore. And the simple Get function does work on these guys.

Any thoughts?

[Dave Cheney]

You haven't shown the definition for the Argument type. 

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[Tomi Hiltunen]

type Argument struct {

// General

Id string

Text string

Creator int64

CreatedAt time.Time

IsPositive bool

// Seconders

Seconders int64

}

[Dave Cheney]

Weird. Sorry if I missed that before. I wonder if it is the time.Time.Location field that is leaking that field in there. 

[Tomi Hiltunen]

Nah, it wasn't there yet. Apparently this online UI mistook it as a quote.

time.Time should be a supported datastore property type. This only happens on GetMulti. Normal Get works just fine. The case here is that I'm trying to pull all the debates where the current user has participated. This includes pulling the participation details to get the debate keys. When I have the right keys, I use GetMulti to get the corresponding debates. This is tricky, but I think I need to make changes to the data structure to get around this issue.

[David Symonds]

Try fetching into []*Debate instead.

[Tomi Hiltunen]

Hi David,

I tried that also. I got a different error stating "cannot use &debates (type *[]*Debate) as type *[]Debate in return argument"

- Tom

keskiviikko, 10. heinäkuuta 2013 12.16.40 UTC+3 David Symonds kirjoitti:

Try fetching into []*Debate instead.

[Tomi Hiltunen]

Hi David,

I just realized my mistake on the last comment. I fixed the return values of the function, and now I'm back to datastore errors: "datastore: invalid entity type"

[Tomi Hiltunen]

I was too quick to comment. It is working now as it is expected to. Here's how it looks now:

Note: debateKeys ==> []*datastore.Key

// Initiate debate interface.

debates := make([]*Debate, len(debateKeys))

for idx, _ := range debates {

debates[idx] = &Debate{}

}

// Get the actual debates from the datastore

if err := datastore.GetMulti(c, debateKeys, debates); err != nil {

return nil, err

}

Without the for-loop, it will give a "invalid entity" error from the datastore.

Thanks for helping me figure this out! :)

[David Symonds]

Actually all you should need to do is

debates := make([]Debate, len(debateKeys))

See the docs: https://developers.google.com/appengine/docs/go/datastore/reference#GetMulti

[Tomi Hiltunen]

I changed it to what you described and it works well. 

I had it like that at one point, though, but still got the "invalid type" error. Perhaps it was some browser caching or build issue... or just too much coffee. :)

Thanks for your time.

Cheers,

Tomi