Golang revel+mgo - no data returned when struct variables having lowercase names

Question

This is my struct type

type Category struct {
    Name string     `bson:"listName"`
    Slug string     `bson:"slug"`
}

used with the following function to return all results from a mongo collection -

func GetCategories(s *mgo.Session) []Category {
    var results []Category
    Collection(s).Find(bson.M{}).All(&results)
    return results
}

The problem is that the field names in my db have names starting in lowercase but the Golang struct returns null when I try to use variable names starting with lower case. For e.g. this returns a JSON with corresponding fields empty -

type Category struct {
    listName string `bson:"listName"`
    slug string     `bson:"slug"`
}

I'm actually porting a Meteor based API to Golang and a lot of products currently using the API rely on those field names like they are in the db! Is there a workaround?

Also, please do not ignore errors. Collection(s).Find(bson.M{}).All(&results) should check for the returned value ( type error ) to be nil. blog.golang.org/error-handling-and-go — Ezequiel Moreno
– Ezequiel Moreno, Commented Aug 3, 2016 at 5:40

Ezequiel Moreno · Accepted Answer · 2016-08-03 05:35:54Z

1

You need to make your fields visible for mgos bson Unmarshall by naming them with a starting capital letter. You also need to map to the appropiates json/bson field names

type Category struct {
    ListName string      `json:"listName" bson:"listName"`
    Slug string          `json:"slug"     bson:"slug"`
}

edited Aug 3, 2016 at 5:35

answered Aug 3, 2016 at 4:25

Ezequiel Moreno

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3 Comments

Gaurav Ojha Over a year ago

This - type Category struct { ListName string bson:"listName" Slug string bson:"slug" } Returns this - { "ListName": "Trimmer/Epilator", "Slug": "trimmer" }, Whereas, this - type Category struct { ListName string json:"listName" Slug string json:"slug" } Returns this - {"listName": "", "slug": "trimmer" }, Which is actually closer to what I'd want. I want the field names to be there in the json just as they are.

Ezequiel Moreno Over a year ago

add bson:"listName" json:"listName"

Gaurav Ojha Over a year ago

Please include this in the answer and I can mark it as correct! You're awesome!

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