Unmarshal struct attributes

[henrmota]

Add the ability to marhsal and unmarhsal custom struct attributes as well custom struct slices, either pointers or not

[mkarlesky]

@shwoodard What needs to happen for this PR to be merged? It appears to fix issues #156 and #164. I confess that there are subtle issues involved that I don't fully grasp. But, I believe I want to use the fixes of this PR instead of relying on a commit from March before the unmarshaling issues were introduced.

[fabrepe]

Any news on this PR ? Why cannot it be merged ?
While this is not merged we need to use @henrmota repository as go module.

[mellena1]

I would also like to see this merged if possible. I am in agreement with @mkarlesky in the sense that I don't grasp some of the subtle issues, but I think this is an important feature to have.

[codyaray]

@shwoodard @aren55555 @Slemgrim can one of you provide a status update on this issue? What are the blockers to merging? What's missing / doesn't work as expected / etc?

EDIT:

I just tested this and it didn't really do what I hoped/expected. I have a struct generated by gogo proto that looks like

type Environment struct {
	Id                   string           `protobuf:"bytes,1,opt,name=id,proto3" json:"id,omitempty" jsonapi:"primary,Environment" db:"id,omitempty" url:"id,omitempty"`
	Name                 string           `protobuf:"bytes,2,opt,name=name,proto3" json:"name,omitempty" jsonapi:"attr,name" db:"name,omitempty" url:"name,omitempty"`
	Created              *types.Timestamp `protobuf:"bytes,6,opt,name=created,proto3" json:"created,omitempty" jsonapi:"attr,created_at" db:"created,omitempty" url:"created,omitempty"`
       ...
}

Normally protobuf's jsonpb marshaller will automatically serialize *types.Timestamp as a nice ISO datetime string. But the current version of jsonapi marshals it as its underlying components like normal encoding/json does (that is, "created": {"seconds": 234234, "nanos": 12342}). And the Payloader object returned from the jsonapi marshaller isn't a proto.Message so you can't just use jsonpb anymore.

So I tried writing a custom marshaller like

func (m *Environment) MarshalJSON() ([]byte, error) {
	s := jsonpb.Marshaler{}
	created, err := s.MarshalToString(m.Created)
	if err != nil {
		return nil, err
	}
	modified, err := s.MarshalToString(m.Modified)
	if err != nil {
		return nil, err
	}
	type Alias Environment
	return json.Marshal(&struct {
		Created  string `json:"created"  jsonapi:"attr,created_at"`
		Modified string `json:"modified" jsonapi:"attr,modified_at"`
		*Alias
	}{
		Created:  created,
		Modified: modified,
		Alias:    (*Alias)(m),
	})
}

But that's never even called by the current version of jsonapi. So I tried this PR hoping it was going to use my custom marshallers for these fields, but instead the output is now {"created_at": null}.

I stepped through the debugger and see that its now trying to treat *types.Timestamp as a relationship-type field to be sideloaded. Specifically, we're now hitting this line of code: https://github.com/google/jsonapi/pull/163/files#diff-b01558cabf60ed66d8a2c08b2bfaba31R381 and nested is coming back as a completely empty Node struct. And because Attributes is nil, created_at is set to nil by node.Attributes[args[1]] = nested.Attributes. (Remember, created_at is the value of args[1] and args[0] is attr) .

I ended up on this PR because of #156 but this doesn't seem to be related, or the PR doesn't really work, or I'm doing something wrong, or all of the above. But I thought I'd share what I was trying/looking for while I'm here. :)