Need support for `omitempty` & `-` on attr fields.

[thedodd]

There are conditions where a model is used in different circumstances, for different responses, and a field may be present, or not present depending on the circumstance. Standard library supports the omitempty and - tokens in the json:"" tag. It would be great to offer the same thing here.

Maybe a third value can be passed: jsonapi:"attr,myfield,omitempty" or something of the sort.

[aren55555]

Given a struct like:

type Book struct {
    ID          int
    Author      string    `json:"author"`
    Title       string    `json:"title,omitempty"`
    PublishedAt time.Time `json:"-"`
}

You would expect JSON like:

{
    "ID": 1,
    "author": "aren55555"
}

Note the title key/value are only present if the Book.Title had a value.

When it comes to the jsonapi struct field tag; there is no - option as fields without a jsonapi are simply ignored.

type Book struct {
    ID          int    `jsonapi:"primary,books"`
    Author      string `jsonapi:"attr,author"`
    Title       string `jsonapi:"attr,title,omitempty"`
    PublishedAt time.Time
}

{
    "data": {
        "type": "books",
        "id": "1",
        "attributes": {
            "author": "aren55555",
        }
    }
}

Note the data.attributes.title key/value are only present if the Book.Title had a value that was not ""

As it currently stands the omitempty option only actually works on Struct fields of the string type.

[thedodd]

Ahh. That is the issue I was running into then. For non-string type fields, I was observing that it did not work. I'd be happy to create a PR which will omitempty fields of other types with their zero-value. Thoughts?

[aren55555]

@thedodd I had already started on this yesterday; here is the Pull Request: https://github.com/shwoodard/jsonapi/pull/35

[thedodd]

@aren55555 you rock. Looking now.