api/models/stories/add-tag.go

package stories

import (
	"errors"

	"git.aiterp.net/rpdata/api/models"
	"github.com/globalsign/mgo/bson"
)

// ErrTagAlreadyExists is an error returned by Story.AddTag
var ErrTagAlreadyExists = errors.New("Tag already exists on story")

// AddTag adds a tag to the story. It returns ErrTagAlreadyExists if the tag is already there
func AddTag(story models.Story, tag models.Tag) (models.Story, error) {
	for i := range story.Tags {
		if story.Tags[i].Equal(tag) {
			return models.Story{}, ErrTagAlreadyExists
		}
	}

	err := collection.UpdateId(story.ID, bson.M{"$push": bson.M{"tags": tag}})
	if err != nil {
		return models.Story{}, err
	}

	story.Tags = append(story.Tags, tag)

	return story, nil
}